Imazamox ammonium salt at 53 g ae/ha applied postemergence in the fall to imidazolinone-resistant wheat controlled Italian ryegrass 98 to 100% 10 wk after treatment (WAT). Control 22 WAT was 88 to 98% at two locations and 55% at a third location. Imazamox was more effective applied in fall to three- to four-leaf Italian ryegrass than when applied in spring to one- to three-tiller Italian ryegrass. Split applications, with 27 g/ha applied in fall and spring, were no more effective than 53 g/ha applied in fall. Pendimethalin preemergence in combination with fall-applied imazamox increased control 22 WAT 10 to 33 percentage points at two of three locations. Imazethapyr ammonium salt plus imazapyr isopropylamine salt applied at 47 plus 16 g ae/ha and imazamox at 44 or 53 g/ha were similarly effective, whereas imazethapyr at 70 g/ha was ineffective. Control by imazapic ammonium salt at 70 g ae/ha was equal to or greater than control by imazamox at 44 or 53 g/ha. Imazamox, imazethapyr plus imazapyr, and imazapic controlled diclofop-resistant and -susceptible Italian ryegrass. Thifensulfuron plus tribenuron mixed with imazamox increased Italian ryegrass control in field and greenhouse experiments, whereas dicamba reduced control compared with imazamox applied alone. Control by imazamox plus 2,4-D was similar to or greater than control by imazamox alone.

Nomenclature: Dicamba; diclofop; imazamox; imazapic; imazapyr; imazethapyr; imidazolinone; isopropylamine; pendimethalin; thifensulfuron; tribenuron; 2,4-D; Italian ryegrass, Lolium multiflorum Lam. Marshall #³ LOLMU; wheat, Triticum aestivum L.

Additional index words: Herbicide interactions, herbicide-resistant weeds, weed management.

Abbreviations: DAT, days after treatment; I₈₀, rate required for 80% visible control or 80% fresh weight reduction; IR, imidazolinone-resistant; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions.

Nomenclature: HOE 404, 2-ethoxyphenyl [[(4,6-dimethoxy-2-pyrimidinyl) amino]carbonyl]sulfamate; MON 37500, N-[[(4,6-dimethoxy-2-pyrimidinyl) amino] carbonyl]-2-(ethylsulfonyl)imidazo[1,2-a]pyridine-3-sulfonamide; rimsulfuron; SL-160, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonyl]-3-(trifluoromethyl)-2-pyridinesulfonamide; Egyptian broomrape, Orobanche aegyptiaca Pers. #³ ORAAE; tomato, Lycopersicon esculentum Mill.

Additional index words: Activated charcoal, Orobanche control, parasitic weeds.

Abbreviations: DAP, days after planting; POST, postemergence; PPI, preplant incorporated.

The presence of row crops, such as field corn, improves herbicidal control of weeds, but the impact of crop row position on herbicide dose–response relationships for weeds is unknown. At midseason at three site-years in Missouri, total weed cover (WC) was reduced by increasing soil residual herbicide rate in a dose-dependent response and was as much as 20% lower in-row (IR) than between-row (BR). Preemergence atrazine S-metolachlor clopyralid flumetsulam at different rates (0×, 0.25×, 0.5×, 0.75×, and 1×, where 1× rate was 2,240 1,750 210 67 g ai/ha, respectively) were applied at planting in field corn to control giant foxtail, the chief weed present, and annual broadleaf weeds, largely common waterhemp. Lower herbicide rates were required to reduce IR WC to the same extent as BR WC, but these rates varied between site-years. At all three site-years, a least squares regression equation adequately described data variability relating corn yield to IR or BR WC (or both) (i.e., Y = a bBR², where Y is corn yield in kg/ha, BR is BR WC [%], and a and b are coefficients).

Nomenclature: Atrazine; clopyralid; flumetsulam; glyphosate; S-metolachlor; common waterhemp, Amaranthus rudis Sauer #³ ATATA; giant foxtail, Setaria faberi (L.) Beauv. # SETFA; corn, Zea mays (L.) # ZEAMX, ‘Pioneer 33G28’.

Additional index words: Band herbicide application, banding, competition, herbicide, reduced rate herbicide, weed, AMBEL, ATATA, POLPE, POLPY, SETFA, XANST, ZEAMX.

Abbreviations: BR, between-row; IR, in-row; WC, weed cover.

Current plant bioassays included in the guidelines for testing pesticides do not include the measurement of reproduction endpoints. A bioassay, based on reduction of flowering of cress was developed to detect soil residues of hexazinone and simazine at levels of 0.02 and 0.10 ppm, respectively. The endpoint used in the described bioassay is the percentage of plant viability that implies that the tested plants have reached the flowering stage. It was found that sensitivity of cress is lower in soils containing higher organic matter.

Nomenclature: Hexazinone; simazine; Cress, Lepidium sativum L. var. Cresson.

Additional index words: Dose–response curves, triazine herbicides.

Abbreviations: DAS, days after sowing.

Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.

Nomenclature: Persian darnel, Lolium persicum Boiss. & Hoh. #³ LOLPS; canola, Brassica napus Koch.; spring wheat, Triticum aestivum L.; sunflower, Helianthus annuus L.

Additional index words: Modeling, rooting depth, seeding rate, seedling establishment, weed interference, yield components, yield loss.

Abbreviations: MSU, Montana State University; NGP, Northern Great Plains.

Field studies were conducted to examine the effects of the sulfonylurea-tolerant (ST) soybean and fall tillage on reducing rotational soybean response to soil-applied prosulfuron across a range of soil pH values. Prosulfuron (10 and 20 g ai/ha) was applied in the fall to simulate the maximum amount of carryover theoretically possible from corn weed control systems. ST soybean reduced effects of prosulfuron soil residues on soybean grain yield. Increased soil pH led to greater prosulfuron carryover as indicated by the differential in ST and non-ST soybean and grain yield responses. Tillage (chisel plow) did not decrease non-ST soybean response to prosulfuron soil residues. Soybean injury 30 d after emergence was well correlated with eventual yield losses in non-ST soybean. Greater soybean injury and yield loss was observed on a silt loam soil with 0.8% organic carbon than on silt loams with greater than 2.5% organic carbon.

Nomenclature: Prosulfuron; corn, Zea mays L.; soybean, Glycine max (L.) Merr. ‘Asgrow 3601,’ ‘Asgrow 3701.’

Additional index words: Herbicide carryover, herbicide degradation, herbicide persistence, soil pH, tillage.

Abbreviations: DAE, days after emergence; SDD₁₀, soil degree day, temperature base of 10 C; ST, sulfonylurea tolerant; SU, sulfonylurea.

Field studies were conducted to determine the sensitivity of conventional ‘Motte’ and ‘Pioneer 9831’ soybean to simulated glyphosate drift rates applied during vegetative and reproductive development and the effect of glyphosate on progeny. Glyphosate at 8, 84, and 420 g ae/ha was applied to soybean at the V3, V6, R2, and R5 growth stages. Glyphosate at 8 and 84 g/ha did not reduce soybean plant population, growth, or yield or cause deleterious effects on progeny, regardless of the growth stage at application. Soybean population, growth, and yield were reduced as much as 99 to 100% after application of 420 g/ha glyphosate at the V3 growth stage. Glyphosate at 420 g/ha applied at V6 was less detrimental to soybean compared with the V3 timing. Delaying the application of 420 g/ha glyphosate until R2 and R5 reduced soybean yields 22 to 49% and 43 to 44%, respectively. Soybean injury from 420 g/ha glyphosate was generally transient or less severe when applied at the V6 growth stage or later. However, 420 g/ha glyphosate at R5 (initial podfill) caused a 390 to 450 kg/ha yield reduction compared with the V6 application, which indicated greater soybean vulnerability to glyphosate drift during podfill than in the late-stage vegetative development. Although glyphosate at 420 g/ha was injurious to soybean, regardless of application timing, progeny was not affected.

Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. ‘Motte’, ‘Pioneer 9831’.

Additional index words: Glyphosate tolerance, herbicide drift, herbicide injury, off-target movement, soybean injury, spray drift.

Abbreviation: WAE, weeks after emergence.

Cotton boll weevil has been eradicated from much of the U.S. Cotton Belt. After eradication, a containment program is necessary to detect and destroy reintroduced boll weevils. Crops other than cotton are not monitored for boll weevil, hence fruit on volunteer glyphosate-resistant (GR) cotton in GR soybean could provide oviposition sites for boll weevils and allow the insects to build up undetected. An experiment was conducted at five locations to evaluate control of GR cotton and reduction in cotton fruit production by herbicides commonly used on GR soybean. Cotton control by preemergence (PRE) or postemergence (POST) herbicides alone was inconsistent across locations. Flumetsulam at 45 g ai/ha, imazaquin at 137 g ai/ha, and metribuzin at 360 g ai/ha plus chlorimuron at 60 g ai/ha applied PRE controlled cotton 55 to 100% and reduced cotton fruit production 84 to 100%. Sulfentrazone at 167 g ai/ha plus chlorimuron at 34 g/ha PRE controlled cotton 50 to 91% and reduced fruit 48 to 98%. Metribuzin PRE at 420 g/ha controlled cotton 23 to 97% and reduced fruit 32 to 100%. Flumiclorac at 30 g ai/ha, 2,4-DB dimethylamine salt at 35 g ae/ha, chlorimuron at 12 g ai/ha, and the sodium salt of fomesafen at 420 g ai/ha mixed with glyphosate and applied POST controlled cotton 48 to 100% and reduced fruit production 67 to 100%. Cloransulam at 12 or 18 g ai/ha controlled cotton 3 to 66% and reduced fruit production 5 to 85%. Cotton control and fruit reduction were greatest and most consistent with sequential applications of metribuzin plus chlorimuron PRE followed by chlorimuron, flumiclorac, fomesafen, or 2,4-DB POST. These treatments controlled cotton at least 95% at all locations. Cotton fruit was totally eliminated at three locations and reduced at least 97% at a fourth location.

Nomenclature: Chlorimuron; cloransulam; 2,4-DB; flumetsulam; flumiclorac; fomesafen; glyphosate; metribuzin; sulfentrazone; cotton, Gossypium hirsutum L. ‘DP 422 B/RR’, ‘PM 1218 B/RR’; soybean, Glycine max (L.) Merr. ‘A5353RR’, ‘A5802RR’, ‘A5901RR’.

Additional index words: Boll weevil eradication, chlorimuron, cloransulam, flumetsulam, flumiclorac, fomesafen, metribuzin, oviposition sites, sulfentrazone, 2,4-DB.

Abbreviations: DAP, days after planting; GR, glyphosate-resistant; POST, postemergence; PRE, preemergence.

Field trials were conducted in 1995 through 2002 to expand the development of chicory by determining the potential for tank mixtures of benefin, trifluralin, or pronamide applied preplant incorporated (PPI) and triflusulfuron methyl or imazamox postemergence (POST) for selective weed control in chicory. Lack of early-season weed control resulted in an 88% reduction in chicory root yield in 1995 to 1996 and an 85% reduction in 2001 to 2002 and demonstrated the susceptibility of chicory plants to early-season weed competition. In the first experiment, pronamide at 1.1 kg ai/ha PPI plus benefin at 1.3 kg ai/ha or trifluralin at 0.56 kg/ha were selective for chicory and controlled weed populations 90% on average with root yields that were 89% of the hand-weeded treatment. Triflusulfuron methyl POST at 17 g/ha caused early-season chicory injury. In the second experiment, trifluralin PPI at 0.56 kg/ha followed by imazamox POST at 36 g/ha controlled weeds 95% on average with a chicory root yield of 74 t/ha, which was 109% of the yield of the hand-weeded treatment.

Nomenclature: Benefin; imazamox; pronamide; trifluralin; triflusulfuron methyl; chicory, Cichorium intybus L. ‘Orchies’.

Additional index words: Belgium endive, competition, root yield.

Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Nine herbicides were tested in a field trial during 2001 and 2002 for the ability to suppress growth of established plants of yellow old world bluestem (OWB) that had invaded native vegetation in central Kansas. Herbicide treatments were applied to OWB at the V4 stage of growth using the Nebraska staging method. At 9 wk after treatment (WAT), plots treated with imazapyr at 1.40 kg ai/ ha had much lower OWB plant frequency than the untreated plots, and plots sprayed with imazapyr and bromacil at 7.84 kg ai/ha had much lower OWB tiller densities than the control plots. Imazapyr and glyphosate at 3.36 kg ai/ha provided greater OWB control than other herbicides. At the first frost after treatment application, imazapyr and bromacil treatments continued to have lower OWB frequency and tiller density than the control plots. Visible herbicide control was closely related to end-of-season yield (R = −0.97). Imazapic at 0.16 kg ai/ha, glyphosate, sulfometuron at 0.21 kg ai/ ha, bromacil, and imazapyr controlled OWB from 54 to 94%. Split applications, altered timing of herbicide application, or varied rates of herbicides that exhibited suppressive potential may further improve efficacy of these herbicides.

Nomenclature: Bromacil; glyphosate; imazapic; imazapyr; sulfometuron; yellow bluestem, Bothriochloa ischaemum (L.) Keng #³ DIHIS.

Additional index words: Biomass, frequency, native vegetation, old world bluestem, suppression, tiller density.

Abbreviations: CRP, conservation reserve program; OWB, old world bluestem; WAT, weeks after treatment.

Triazine-resistant common lambsquarters (TR-CHEAL) is a widespread weed problem in the northcentral United States. Field studies were conducted from 1995 to 1997 to determine the efficacy and consistency of metolachlor, pendimethalin, and acetochlor applied preemergence (PRE) for control of TR-CHEAL in corn. Pendimethalin provided greater (98%) and more consistent control of TR-CHEAL than metolachlor (66%) or acetochlor (86%). Studies were conducted from 1998 to 2000 to examine the potential of isoxaflutole, flumetsulam, and rimsulfuron plus thifensulfuron for control of TR-CHEAL in corn. In 1999 and 2000, isoxaflutole (35 g ai/ha), flumetsulam (35 g ai/ ha), and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 98% or greater control of TR-CHEAL. In 1998 when rainfall was limited after application, isoxaflutole (70 g ai/ha) and flumetsulam (70 g ai/ha) provided 65 and 55% control, respectively, and rimsulfuron plus thifensulfuron (26 g ai/ha) provided 55% control. Results indicate that control of TR-CHEAL with currently labeled PRE herbicides is possible.

Nomenclature: Acetochlor; flumetsulam; isoxaflutole; metolachlor; pendimethalin; rimsulfuron; thifensulfuron; triazine; common lambsquarters, Chenopodium album L. #³ CHEAL; corn, Zea mays L.

Additional index words: Herbicide resistance.

Abbreviations: OM, organic matter; POST, postemergence; PRE, preemergence; TR-CHEAL, triazine-resistant common lambsquarters.

Paraquat applied from mid-February through early April over 2 yr was evaluated for sugarcane tolerance and Italian ryegrass control. Sugarcane 31 cm tall at application was injured 16 to 25% and 8 to 14% 28 and 56 d, respectively, after mid-March application of paraquat at 0.35 or 0.70 kg ai/ha. Early-April application to 61-cm-tall sugarcane caused 13 to 25% injury. The observed injury was not reflected in reduced sugarcane shoot population or height or sugarcane or sugar yield when compared with diuron, the standard herbicide treatment. Italian ryegrass control 28 d after the mid-February application of paraquat alone at 0.53 or 0.70 kg/ha was variable, ranging from 80% in 1994 to no more than 66% in 1995. For each year, diuron at 3.2 kg/ha in combination with both rates of paraquat increased Italian ryegrass control 28 d after the mid-February application 11 to 17 percentage points. At 56 d after the mid-February application, addition of diuron proved beneficial only in 1994 when the paraquat and diuron combinations controlled ryegrass 93% compared with no more than 62% for paraquat applied alone. In contrast, Italian ryegrass was controlled the second year no more than 80% 56 d after the mid-February application of paraquat alone or with diuron. Paraquat applied at 0.70 kg/ha with diuron in mid-March controlled Italian ryegrass 80 and 86% 28 d after treatment in 1994 and 1995, respectively. For the standard herbicides metribuzin, terbacil, and diuron applied in mid-March, weed control was no greater than 38%. Although differences in Italian ryegrass control among herbicide treatments were observed, efficacy was sufficient to reduce weed competition such that sugarcane growth and yield were not negatively affected.

Nomenclature: Diuron; metribuzin; paraquat; terbacil; Italian ryegrass, Lolium multiflorum Lam. #³ LOLMU; sugarcane, Saccharum spp. # SACCH ‘CP 70-321’, ‘LHO 83-153’.

Additional index words: Application timing, crop tolerance, weed–crop competition.

Abbreviations: DAT, days after treatment; PRE, preemergence; TRS, theoretically recoverable sugar.

Field experiments were conducted to evaluate chemicals for silvery-thread moss control and bentgrass turfgrass quality. Treatments included iron (Fe)-containing products, nitrogen fertilizers, Ultra Dawn dishwashing detergent (UD) at 3% (v/v), and oxadiazon. In general, greater silvery-thread moss control was achieved with Fe-containing products. Ferrous sulfate at 40 kg Fe/ha plus ammonium sulfate at 30 kg N/ha, a combined product of ferrous oxide, ferrous sulfate, and iron humates (FEOSH) at 125 kg Fe/ha, and a combined product of iron disulfide and ferrous sulfate (FEDS) at 112 kg Fe/ha reduced silvery-thread moss populations 87, 81, and 69%, respectively, 6 wk after initial treatment (WAIT). UD reduced silvery-thread moss populations 57% 6 WAIT. The addition of oxadiazon to Fe-containing treatments did not improve silvery-thread moss population reduction. Other experiments evaluated two formulations of chlorothalonil, each applied at two rates, chlorothalonil with zinc at 9.5 and 17.4 kg ai/ha and chlorothalonil without zinc at 9.1 and 18.2 kg/ ha, and two spray volumes (2,038 and 4,076 L/ha). Greater silvery-thread moss population reduction was observed at Jefferson Landing in 1999 compared with Elk River in 1999 and 2000. Rainfall events at Elk River in 1999 and 2000 within 24 h after application and no rain at Jefferson Landing may account for variation in performance of products between sites. However, no difference in chlorothalonil formulation, rate, or spray volume was observed in any location or year. These data indicate that Fe-containing fertilizers or chlorothalonil can be used to reduce silvery-thread moss populations in creeping bentgrass putting greens.

Nomenclature: Chlorothalonil, tetrachloroisophthalonitrile; oxadiazon; silvery-thread moss, Bryum argenteum Hedw.; creeping bentgrass, Agrostis palustris Huds. ‘Penncross’.

Additional index words: Bryology, moss control, turfgrass injury.

Abbreviations: BM, Black Mountain Golf Club; ER, Elk River Country Club; JL, Jefferson Landing Golf Club; MNP, micronutrient package; NPK, 20:20:20 nitrogen–phosphorus–potassium; UD, Ultra Dawn dishwashing detergent; WAIT, weeks after initial treatment.

Ground ivy is an invasive, perennial, broadleaf weed common in turf sites. A recent survey of lawn care professionals suggests ground ivy populations respond differently to herbicides. Our study was conducted to determine the variation in response among and within ground ivy populations to 2,4-D or triclopyr application. Ground ivy populations were sampled from nine sites in the United States and Canada. Leaf width, petiole length, and internode length varied by population by as much as 31, 36, and 45%, respectively. In a greenhouse study, applying 4.5 kg/ha 2,4-D or 0.9 kg/ha triclopyr to all populations resulted in a phytotoxic response that varied according to population by as much as 47% for 2,4-D and 31% for triclopyr. Random-amplified polymorphic DNA analysis identified 52 genotypes in the nine populations, and these genotypes varied in response to 2,4-D application in some populations. Difficulty in control of ground ivy with 2,4-D or triclopyr may be because of the presence of ecotypes and biotypes.

Nomenclature: 2,4-D; triclopyr; ground ivy, Glechoma hederacea L. #³ GLEHE.

Additional index words: Biotype, ecotype, herbicide screening, resistance, tolerance.

Abbreviations: DAT, days after treatment; FW, fresh weight; LCO, lawn care operator; RAPD, random-amplified polymorphic DNA; RFW, regrowth fresh weight.

Recent advances in genetic engineering have led to the development of glyphosate-resistant (GR) crops for genetic markers and selective weed control. The effects of glyphosate residue on turfgrass clippings could be toxic to non-GR species. The objective of this experiment was to determine whether glyphosate would retain activity within clippings of creeping bentgrass when applied to Kentucky bluegrass and perennial ryegrass. Greenhouse-grown ‘Penncross’ and GR ‘ASR-368’ were treated with glyphosate at 2.24 kg/ha. Clippings were collected 1, 3, 7, and 12 d after application and applied to greenhouse-grown Kentucky bluegrass and perennial ryegrass. Kentucky bluegrass and perennial ryegrass dry weight and percent cover were reduced by clippings receiving glyphosate that were harvested 1 and 3 d after glyphosate application from both susceptible and resistant creeping bentgrass. Results indicate that glyphosate remains active in clippings for up to 3 d after treatment within creeping bentgrass clippings. Glyphosate-applied creeping bentgrass clippings will need to be managed to prevent injury to susceptible species.

Nomenclature: Glyphosate; creeping bentgrass, Agrostis stolonifera L.; Kentucky bluegrass, Poa pratensis L.; perennial ryegrass, Lolium perenne L.

Additional index words: Clippings, glyphosate, mulch, turfgrass.

Abbreviations: DAT, days after treatment; GR, glyphosate resistant; GRCB-G, glyphosate-resistant creeping bentgrass treated with glyphosate; PCB-G, Penncross creeping bentgrass treated with glyphosate; PCB-UTC, Penncross creeping bentgrass untreated control; UTC, untreated control.

Natural product herbicides for vegetation control are being considered as alternatives to synthetic herbicides by many public agencies. Studies were conducted along roadsides at the Hopland Research and Extension Center (HREC) in 2001 and 2002 and on California State Route 29 (SR29) in 2002 to evaluate acetic acid, pine oil, and plant essentials compared with glyphosate for control of herbaceous vegetation. In 2001, annual grass control after a single application of pine oil at HREC was 40% or less effective, whereas acetic acid was at least 79% effective. A second application of pine oil or acetic acid did not control regrowth or new plants. In 2002, plant essentials was the most effective (>80%) natural product at HREC for control of annual grasses, except slender oat. Pine oil often provided similar control of slender oat as plant essentials (71 and 69%, respectively). At SR29, five applications of acetic acid provided 83% or better control of slender oat, hare barley, medusahead, and broadleaf filaree. Plant essentials and pine oil controlled hairy vetch, broadleaf filaree, and hare barley at least 83%, but yellow starthistle, soft chess, buckhorn plantain, and medusahead control never exceeded 85%. Glyphosate controlled all vegetation in these experiments with one or two applications. The cost of one or more applications of the natural products was greater than 10 times the cost of using one or two applications of glyphosate. Natural products were neither efficaciously nor economically comparable with glyphosate for control of annual roadside vegetation.

Nomenclature: Acetic acid; glyphosate; pine oil; pine oil terpenes; plant essentials; 2-methoxy-4-(2-propenyl)phenol 2-phenethyl propionate; broadleaf filaree, Erodium botrys (Cav.) Bertol. #³ EROBO; buckhorn plantain, Plantago lanceolata L. # PLALA; hairy vetch, Vicia villosa Roth # VICVI; hare barley, Hordeum leporinum L. # HORLE; medusahead, Taeniatherum caput-medusae (L.) Nevski # ELYCM; slender oat, Avena barbata Pott ex Link # AVEBA; soft chess, Bromus mollis L. # BROMO; yellow starthistle, Centaurea solstitialis L. # CENSO.

Additional index words: Chemical weed control, economics, integrated roadside vegetation management.

Abbreviations: DAT, days after treatment; EPA, Environmental Protection Agency; FIFRA, Federal Insecticide, Fungicide and Rodenticide Act; HREC, Hopland Research and Extension Center; SR29, California State Route 29.

Field studies were conducted in South Carolina and Georgia to evaluate weed control and soybean tolerance and yield after nonionic surfactant addition to combinations of chlorimuron plus an adjuvant-containing glyphosate formulation. Treatments included glyphosate alone, at 420 or 840 g ae/ha, or in combination with 6 or 9 g ai/ha chlorimuron and all possible combinations with or without 0.25% (v/v) nonionic surfactant. Other treatments included a weed-free and nontreated check. Chlorimuron plus glyphosate improved entireleaf, smallflower, and tall morningglory control over glyphosate alone, but nonionic surfactant addition did not further improve the control of any species, except tall morningglory. Up to 31% early-season injury was observed with the three-way mixture. Soybean injury was greater, and yields were reduced in one of three trials when nonionic surfactant was added to chlorimuron plus glyphosate combinations. This research indicates that there would be no benefit from the nonionic surfactant addition to this adjuvant-containing glyphosate formulation when combined with chlorimuron.

Nomenclature: Chlorimuron; glyphosate; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #³ IPOHG; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. # IAQTA; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; soybean, Glycine max (L.) Merr.

Additional index words: Adjuvant, crop injury, glyphosate-resistant soybean, herbicide mixtures.

Abbreviations: ALS, acetolactate synthase.

Two experiments, one focusing on preemergence (PRE) herbicides and the other on postemergence (POST) herbicides, were conducted and repeated in time to examine the utility of hyperspectral remote sensing data for discriminating common cocklebur, hemp sesbania, pitted morningglory, sicklepod, and soybean after PRE and POST herbicide application. Discriminant models were created from combinations of multiple indices. The model created from the second experimental run's data set and validated on the first experimental run's data provided an average of 97% correct classification of soybean and an overall average classification accuracy of 65% for all species. These data suggest that these models are relatively robust and could potentially be used across a wide range of herbicide applications in field scenarios. From the data set pooled across time and experiment types, a single discriminant model was created with multiple indices that discriminated soybean from weeds 88%, on average, regardless of herbicide, rate, or species. Signature amplitudes, an additional classification technique, produced variable results with respect to discriminating soybean from weeds after herbicide application and discriminating between controls and plants to which herbicides were applied; thus, this was not an adequate classification technique.

Nomenclature: Common cocklebur, Xanthium strumarium L.; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A.W. Hill; pitted morningglory, Ipomoea lacunosa L.; sicklepod, Sennna obtusifolia (L.) Irwin and Barnaby; soybean, Glycine max (L.) Merr.

Additional index words: Acifluorfen, chlorimuron, hyperspectral imagery, imazaquin, indices, metribuzin, pendimethalin, ROC curve.

Abbreviations: CCC, canonical correlation coefficient; DAA, days after application; DINO, differential index of normalized observations; LDA, linear discriminant analysis; NDVI, normalized difference vegetation index; NIR, near-infrared; POST, postemergence; PRE, preemergence; ROC, receiver operator characteristics; SA, signature amplitudes; SCA, species classification accuracy; SDM, single discriminant model; SWIR, short-wave infrared.

Chemical weed control with acrolein has been shown to be a lower cost method for reducing submerged plant biomass of sago pondweed in the irrigation district of the Lower Valley of Rio Colorado, Argentina (39°10′S–62°05′W). However, no experimental data exist on the effects of the herbicide on plant growth and its survival structures. Field experiments were conducted during 3 yr to evaluate the effect of acrolein on growth and biomass of sago pondweed and on the source of underground propagules (i.e., rhizomes, tubers, and seeds). Plant biomass samples were collected in irrigation channels before and after several herbicide treatments. The underground propagule bank was evaluated at the end of the third year. Within each treatment, plant biomass was significantly reduced by 40 to 60% in all three study years. Rapid new plant growth occurred after each application; however, it was less vigorous after repeated treatments. At the end of the third year at 3,000 m downstream from the application point, plant biomass at both channels ranged from 34 to 3% of control values. Individual plant weight and height were affected by acrolein treatments, flowering was poor, and seeds did not reach maturity. After 3 yr, acrolein did not reduce the number of tubers. However, they were significantly smaller and lighter. Rhizomes fresh weight decreased by 92%, and seed numbers decreased by 79%. After 3 yr of applications, operational functioning of the channels could be maintained with fewer treatments and lower concentrations of acrolein.

Nomenclature: Acrolein; acrylaldehyde; 2-propenal; sago pondweed, Potamogeton pectinatus L.

Additional index words: Aquatic weed control, chemical control, submerged plants, propagule banks.

Abbreviations DW, dry weight.

Biennial wormwood has become a problem for soybean producers in the northern Great Plains of the United States. Research was conducted to evaluate control of biennial wormwood with preemergence (PRE) herbicides alone or followed by postemergence (POST) herbicides in 2000 and 2001 at Fargo, Leonard, and Wyndmere, ND. Favorable soil moisture conditions at Leonard resulted in continual emergence and greater densities of biennial wormwood, whereas the soil at Fargo and Wyndmere was dry and few biennial wormwood seedlings emerged at these locations. Biennial wormwood control with PRE herbicides was greater than 89% at Fargo and Wyndmere but was 80% or lower at Leonard. PRE biennial wormwood control was higher with flumetsulam than with sulfentrazone. When POST treatments were applied after PRE herbicides, biennial wormwood control 4 wk after treatment was 92% or better at Fargo and Wyndmere but was 76% or less at Leonard. The combination of PRE and POST herbicide treatments did not improve control greatly at Fargo or Wyndmere but at Leonard reduced the number of biennial wormwood plants.

Nomenclature: Flumetsulam; sulfentrazone; biennial wormwood, Artemisia biennis Willd. #³ ARTBI; soybean, Glycine max (L.) Merr.

Additional index words: Postemergence, preemergence, weed control, weed density.

Abbreviations: POST, postemergence; PPO, photoporphyrinogen oxidase; PRE, preemergence; WAT, weeks after treatment.

Field studies were conducted in 2000 and 2001 in Plains, GA, to determine peanut and weed response to the residual herbicides sulfentrazone, imazapic, diclosulam, and flumioxazin. Herbicide treatments included sulfentrazone applied preemergence (PRE) or preplant incorporated (PPI) at 112, 168, 224, and 280 g ai/ha, imazapic postemergence (POST) at 71 g ai/ha, diclosulam PPI at 26 g ai/ha, and flumioxazin PRE at 88 g ai/ha. Peanut exhibited early-season injury from all herbicide treatments, ranging from 0 to 10% for sulfentrazone PPI or PRE, 10% for imazapic, 3 to 23% for flumioxazin, and 1 to 7% for diclosulam. Yields were similar for sulfentrazone PPI- or PRE-treated and flumioxazin-, imazapic-, and diclosulam-treated peanut. Yellow nutsedge control was 83% or greater with all rates of sulfentrazone PRE or PPI, 83 and 90% with diclosulam, and 96 and 99% with imazapic, respectively. Flumioxazin did not control yellow nutsedge or wild poinsettia. Tall morningglory control was 82% or greater with imazapic, diclosulam, flumioxazin, and sulfentrazone PPI or PRE at 168 g/ha or higher. Florida beggarweed control was 88% or greater with diclosulam, flumioxazin, and sulfentrazone PRE at 224 and 280 g/ha. Overall, peanut tolerance to sulfentrazone at 112 to 280 g/ha PPI and PRE was high and yield was equivalent to the currently registered peanut residual herbicides.

Nomenclature: Diclosulam; flumioxazin; imazapic; sulfentrazone; Florida beggarweed, Desmodium tortuosum (Sec) L., #³ DEDTO; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; wild poinsettia, Euphorbia heterophylla L. # EPHHL; Yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L.

Additional index words: Peanut injury, peanut yield, susceptibility to herbicides.

Abbreviations: ALS, acetolactate synthase; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; VE, vegetative emergence.

Selective placement studies were conducted under greenhouse conditions to determine the relative importance of root vs. foliar absorption of postemergence-applied quinclorac by torpedograss. Foliar soil and soil-only applications were more effective than foliar-only in reducing torpedograss foliage at 4 wk after treatment (WAT). However, foliar-only and foliar soil were more effective than soil-only in suppressing regrowth at 10 WAT. Quinclorac foliar absorption by torpedograss and subsequent translocation, as determined with radiotracer techniques, was minimal. After 72 h, only 26% of the applied quinclorac had been absorbed, and 13.7% of the amount applied remained within the treated leaf. Only 0.3% of applied was recovered in the roots, and none was detected in the developing rhizomes. Quinclorac was readily root absorbed and translocated. After 6 h, a 26.7 μg/ plant dose of quinclorac had been absorbed, and 54% of this quantity remained in the roots; the remaining 46% having been translocated throughout the plant. The youngest leaf and the immature rhizomes accumulated 5 and 9% of the amount absorbed, respectively. Quinclorac was not readily soil sorbed as determined by soil solution experiments. Quinclorac was displaced nearly concomitant with the wetting front in soil chromatography. Soil solution concentration and soil mobility were greater at pH 6.7 than at 5.7. Results establish that consistent control of torpedograss with quinclorac is dependent on soil entry and root absorption. Unfortunately, the propensity of quinclorac to be water displaced could negatively affect this control.

Nomenclature: Quinclorac; torpedograss, Panicum repens L. #³ PANRE.

Additional index words: Herbicide translocation, soil sorption, soil mobility, soil pH.

Abbreviations: WAT, weeks after treatment; LSS, liquid scintillation spectrometry.

Field studies were conducted to evaluate foramsulfuron for postemergence control of goosegrass in bermudagrass turf as a possible replacement for MSMA. In field trials on a golf course and sports fields planted to bermudagrass, mature goosegrass was controlled effectively (>85% goosegrass dead on the basis of canopy area) with two applications of foramsulfuron plus metribuzin. The herbicide rates that were effective varied among studies, e.g., foramsulfuron at 0.029 or 0.044 kg ai/ha mixed with metribuzin at 0.105 to 0.210 kg ai/ha. Goosegrass was often controlled with MSMA at 2.24 kg ai/ha plus metribuzin at 0.105 to 0.210 kg/ha, but foramsulfuron was always as effective, or more effective, than MSMA, in controlling mature goosegrass, at the same rate of metribuzin. Bermudagrass phytotoxicity of foramsulfuron plus metribuzin was temporary and not different from MSMA plus metribuzin. In one location there was noticeable phytotoxicity 4 wk after initial treatment.

Nomenclature: Foramsulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-4-(formylamino)-N,N-dimethylbenzamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; MSMA, monosodium methanearsonate; hybrid bermudagrass, Cynodon transvaalensis × Cynodon dactylon ‘Tifway’; goosegrass, Eleusine indica (L.) Gaertn.#³ ELEIN.

Additional index words: Alternatives to MSMA, arsenic, golf course, turfgrass.

Abbreviations: OM, organic matter; POST, postemergence; WAIT, weeks after initial treatment.

Experiments were conducted to evaluate safety and effectiveness of herbicides during establishment of seeded centipedegrass. Centipedegrass tolerance to herbicides was evaluated at seeding and early postemergence. Imazapic at 105 g ai/ha, sulfometuron at 53 g ai/ha, or metsulfuron at 21 or 42 g ai/ha applied at seeding reduced centipedegrass ground cover compared with the nontreated. Imazapic at 18 or 35 g/ha or applications of atrazine or simazine at seeding did not reduce centipedegrass ground cover compared with the nontreated. Applications of chlorsulfuron plus mefluidide (7 140 g ai/ha) or metsulfuron at 21 or 42 g/ha applied 6 wk after seeding (WAS) centipedegrass (one-leaf to one-tiller growth stage) caused 20, 16, and 83% phytotoxicity, respectively, 56 d after treatment (DAT). Imazapic, sulfometuron, atrazine, or simazine applied 6 WAS caused <15% phytotoxicity 56 DAT. When large crabgrass and centipedegrass were seeded together, large crabgrass emergence was reduced 41% when atrazine (1,100 g ai/ha) was applied at seeding. Centipedegrass tiller production was reduced with increasing amounts of crabgrass. However, centipedegrass tiller production and ground cover were higher when atrazine was applied because of reduced interspecific interference from large crabgrass. These data indicate that centipedegrass can be established more quickly if appropriate herbicides are used at seeding or shortly after seeding.

Nomenclature: Atrazine; chlorsulfuron; imazapic; mefluidide; metsulfuron; simazine; sulfometuron; large crabgrass, Digitaria sanguinalis (L.) Scop. #³ DIGSA; centipedegrass, Eremochloa ophiuroides (Munro) Hack.

Additional index words: Atrazine, chlorsulfuron, Digitaria sanguinalis, herbicide tolerance, imazapic, interference, large crabgrass, mefluidide, metsulfuron, PGR tolerance, simazine.

Abbreviations: DAS, days after seeding; DAT, days after treatment; PGR, plant growth regulator; WAS, weeks after seeding.

To address grower concerns that repeated use of dichlobenil could negatively affect cranberry productivity, field studies were conducted at two commercial farms in either high weed density (HW) or low weed density (LW) areas. Data from 4 yr of repeat annual applications of 0, 1.8, and 4.5 kg ai/ha dichlobenil indicated minimal negative impact on cranberry vines. Herbicide application did not affect upright productivity, leaf biomass production, percent fruit set, or other yield parameters adversely; in addition, no improvement in these parameters was noted. Although the interaction of herbicide application with weed density on cranberry root length varied with sampling date, no consistent trend (adverse or positive) was seen. The presence of weeds, rather than herbicide application, was the important determinant of yield. Vines in LW areas produced more marketable fruit and had higher percentage of fruit set than vines growing in HW areas. Repeat annual applications of dichlobenil on commercial cranberry beds may be considered as part of a viable integrated weed management program with no adverse effect on crop growth or yield.

Nomenclature: Dichlobenil; cranberry, Vaccinium macrocarpon Ait.

Additional index words: Herbicides, root length, vegetation survey, weed community.

Abbreviations: HW, high weed density; LW, low weed density.

Field experiments were conducted to evaluate control of 90- to 100-cm-tall ragweed parthenium in a noncropped situation in Haryana State, India, during 2000 and 2001. Atrazine, 2,4-D ethyl ester, atrazine plus 2,4-D, metribuzin, metsulfuron, chlorimuron, glufosinate with and without surfactant, glyphosate with and without surfactant, and glyphosate formulations MON 8793 and 8794 were sprayed on ragweed parthenium. Also, the effect of water quality was studied with flat-fan and flood-fan nozzles using glyphosate and its formulation MON 8793 against ragweed parthenium and associated weeds. Glyphosate MON 8793 and 8794 at 3.6 kg ae/ha provided excellent control of ragweed parthenium followed by glyphosate at 2.7 or 5.4 kg/ha, with no recovery until 18 wk after treatment (WAT). Addition of 0.1% v/v surfactant (MON 0818) to glyphosate at 2.7 kg/ha provided similar control to that of glyphosate alone at 5.4 kg/ha. Other herbicides failed to provide satisfactory control of ragweed parthenium. In the water quality study, glyphosate at 2.7 and 5.4 kg/ha and glyphosate MON 8793 at 2.7 and 3.6 kg/ha provided similar control of ragweed parthenium at 18 WAT. Glyphosate was antagonized less by tap water (0.45 mM Ca) than canal (0.7 mM Ca) and hand-pump water (1 mM Ca). Neither glyphosate nor glyphosate MON 8793 provided good control of purple nutsedge, velvetleaf, garden spurge, threelobe false mallow, jimsonweed, giant milkweed, Indian jujube, or tropical spiderwort, but crowfootgrass, green foxtail, sprawling signalgrass, and spiny amaranth were controlled. Glyphosate at 5.4 kg/ha and glyphosate MON 8793 at 3.6 kg/ha provided more than 80% control of bermudagrass at 8 WAT, which was significantly better than the 2.7 kg/ha rate. Flat-fan nozzles provided better efficacy of applied herbicides than flood-fan nozzles at 4 WAT on ragweed parthenium.

Nomenclature: Atrazine; chlorimuron-ethyl; glufosinate; glyphosate; glyphosate MON 8793; glyphosate MON 8794; metribuzin; metsulfuron-methyl; 2,4-D; ragweed parthenium, Parthenium hysterophorus L. #³ PTNHY; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; crowfootgrass, Dactyloctenium aegyptium (L.) Beauv. # DTTAE; garden spurge, Euphorbia hirta L. # EPHHI; giant milkweed, Calotropis procera (Ait.) R. Br.; green foxtail, Setaria viridis (L.) Beauv. # SETVI; Indian jujube, Zizyphus nummularia (Burm. f.) Wight. & Arn.; jimsonweed, Datura stramonium L. # DATST; purple nutsedge, Cyperus rotundus L. # CYPRO; spiny amaranth, Amaranthus spinosus L. # AMASP; sprawling signalgrass, Brachiaria reptans (L.), Gard. & Hubb.; threelobe false mallow, Malvastrum coromandelianum (L.) Garcke.; tropical spiderwort, Commelina benghalensis L. # COMBE; velvetleaf, Abutilon bidentatum L.

Additional index words: Application stage, glyphosate formulations, nozzle types, surfactant, water quality.

Abbreviations: DAT, days after treatment; WAT, weeks after treatment; EC, electrical conductivity.

A fixed-plot management study for control of acetolactate synthase (ALS)–resistant common cocklebur in soybean was initiated in 1994 at Fayetteville, AR. Three susceptible and three imazaquin-resistant common cocklebur plants were transplanted into the field, and seed (burs) were distributed throughout the plots in the fall of 1994. Herbicide treatments included imazaquin, chlorimuron, and chlorimuron plus metribuzin applied each year from 1995 through 1999 and herbicide rotations containing ALS inhibitors and herbicides with alternative modes of action. Effectiveness of management systems and the dynamics of the development of common cocklebur resistance, including development of resistance to imazaquin and chlorimuron, were evaluated. Imazaquin controlled susceptible common cocklebur populations in 1995 but not the resistant population, resulting in significant soybean yield reduction. By the end of the 1996 season, the resistant biotype dominated imazaquin plots, and a high level of cross-resistance to chlorimuron was observed in the population. Resistant populations were reduced by non-ALS herbicide programs of sulfentrazone plus clomazone applied preemergence (PRE), metribuzin plus clomazone applied PRE followed by bentazon applied postemergence (POST), and transgenic herbicide programs of glyphosate and glufosinate applied POST. Rotating ALS inhibitors with non–ALS-inhibiting heribicides may slow the development of resistance, but resistant individuals may eventually dominate the population.

Nomenclature: Bentazon; chlorimuron; clomazone; glufosinate; glyphosate; imazaquin; metribuzin; sulfentrazone; common cocklebur, Xanthium strumarium L. #³ XANST; soybean, Glycine max (L.) Merr. ‘Hutcheson’, ‘Delta King 5580’, ‘Delta King 5961RR’, ‘Asgrow 5547LL’.

Additional index words: ALS resistance, atrazine, chlorimuron resistance, flumetsulam, fluometuron, fomesafen, herbicide resistance management, imazaquin resistance.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence; PRE, preemergence.

White bean producers have a limited number of herbicide options available for annual grass and broadleaf weed control. Tolerance of two white bean cultivars to preemergence (PRE) applications of S-metolachlor, S-metolachlor imazethapyr, flumetsulam S-metolachlor, cloransulam-methyl, clomazone, clomazone imazethapyr, and clomazone S-metolachlor at the maximum labeled rate in soybean (1×) and twice the labeled rate (2×) were studied at two Ontario locations (Exeter and Ridgetown) in 2001 and 2002. S-Metolachlor, clomazone, and clomazone S-metolachlor generally had no negative effect on plant height, dry weight, maturity, and yield. S-Metolachlor imazethapyr and clomazone imazethapyr reduced plant height, dry weight, and yield as much as 21, 42, and 24%, respectively. Flumesulam S-metolachlor and cloransulam-methyl reduced plant height, dry weight, and yield as much as 39, 58, and 43%, respectively. White beans are tolerant to PRE applications of S-metolachlor, clomazone, and clomazone S-metolachlor. White beans are sensitive to PRE applications of S-metolachlor imazethapyr, flumetsulam S-metolachlor, clomazone imazethapyr, and cloransulam-methyl.

Nomenclature: Clomazone; cloransulam-methyl; flumetsulam; imazethapyr; S-metolachlor; soybean, Glycine max (L.) Merr; white bean, Phaseolus vulgaris L.

Additional index words: Dry beans, herbicide tolerance, preemergence herbicides, white beans.

Abbreviations: DAE, days after emergence; PRE, preemergence; 1× rate, the maximum recommended herbicide labeled rate in soybean; 2× rate, twice the maximum recommended herbicide labeled rate in soybeans.

Field studies were conducted in Alabama in 1998 and 1999 to evaluate fomesafen preemergence (PRE) in glyphosate-resistant cotton. Fomesafen (0.3 and 0.4 kg ai/ha), fluometuron (1.4 kg ai/ha), and pyrithiobac (0.05 kg ai/ha) were applied alone or in tank mixtures. Glyphosate (0.4 kg ae/ha) was applied postemergence over-the-top (POT) and postemergence directed (PD). Regardless of PRE treatment, POT followed by (fb) PD applications of glyphosate were necessary for greater than 82% sicklepod control at midseason. In the absence of glyphosate, fomesafen, and fomesafen-containing tank mixtures controlled common cocklebur and Ipomoea species 77 and 72%, respectively, 14 d after PD application. However, two applications of glyphosate were needed for >94% season-long control of common cocklebur and Ipomoea species because of continued germination throughout the growing season. Postemergence applications of glyphosate added a 1,000 kg/ha seed cotton yield increase to all PRE treatments at both locations. Common cocklebur, Ipomoea species, and sicklepod control was not significantly increased by the addition of fomesafen PRE tank mixtures fb glyphosate postemergence as compared with glyphosate postemergence only.

Nomenclature: Fluometuron; fomesafen; glyphosate; pyrithiobac; common cocklebur, Xanthium strumarium L. #³ XANST; Ipomoea species # IPOSS; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; cotton, Gossypium hirsutum L. ‘Deltapine 655 BG/RR’, ‘Paymaster 1220 BG/ RR’.

Additional index words: CASOB, fluometuron, fomesafen, glyphosate, glyphosate timing, pyrithiobac, residual herbicide, Senna obtusifolia, soil-applied herbicide, transgenic cotton, XANST, Xanthium strumarium.

Abbreviations: fb, followed by; PD, postemergence directed; POT, postemergence over-the-top; PRE, preemergence; SRS, Syngenta Research Site; WGS, Wiregrass Research and Education Center.

Evaluation of economic outcome associated with a given weed management system is an important component in the decision-making process within crop production systems. The objective of this research was to investigate how risk-efficiency criteria could be used to improve herbicide-based weed management decision making, assuming different risk preferences among growers. Data were obtained from existing weed management trials in corn conducted at the University of Minnesota Southern Research and Outreach Center at Waseca. Weed control treatments represented a range of practices including one-pass soil-applied, one-pass postemergence, and sequential combinations of soil and postemergence herbicide application systems. Analysis of risk efficiency across 23 herbicide-based weed control treatments was determined with the mean variance and stochastic dominance techniques. We show how these techniques can result in different outcomes for the decision maker, depending on risk attitudes. For example, mean variance and stochastic dominance techniques are used to evaluate risk associated with one- vs. two-pass herbicide treatments with and without cultivation. Based on these analyses, it appears that a one-pass system is preferred by a risk-averse grower. However, we argue that this may not be the best option considering potential changes in weed emergence patterns, application timing concerns, etc. The techniques for economic analysis of weed control data outlined in this article will help growers match herbicide-based weed management systems to their own production philosophies based on economic risk.

Nomenclature: Corn, Zea mays L.

Additional index words: Analysis of variance, mean variance procedure, stochastic dominance.

Abbreviations: CV, coefficient of variation; FSD, first-degree stochastic dominance; POST, postemergence; PRE, preemergence; SSD, second-degree stochastic dominance.

Field studies were conducted to evaluate weed control with combinations of glyphosate at 750 g ae/ha and the insecticides acephate (370 g ai/ha), dicrotophos (370 g ai/ha), dimethoate (220 g ai/ha), fipronil (56 g ai/ha), imidacloprid (53 g ai/ha), lambda-cyhalothrin (37 g ai/ha), oxamyl (280 g ai/ha), or endosulfan (420 g ai/ha) and insect control with coapplication of the herbicide with insecticides acephate, dicrotophos, dimethoate, and imidacloprid. Applying lambda-cyhalothrin or fipronil with glyphosate reduced control of hemp sesbania by 19 and 9 percentage points, respectively, compared with glyphosate alone. Acephate, dicrotophos, dimethoate, imidacloprid, lambda-cyhalothrin, oxamyl, and endosulfan did not affect hemp sesbania, pitted morningglory, prickly sida, and redweed control by glyphosate. Lambda-cyhalothrin and fipronil did not affect glyphosate control of weeds other than hemp sesbania. Addition of glyphosate to dicrotophos improved cotton aphid control 4 d after treatment compared with dicrotophos alone. Thrips control was improved with addition of glyphosate to imidacloprid. Insect control was not reduced by glyphosate regardless of insecticide.

Nomenclature: Acephate, O, S-dimethyl acetylphosphoramidothioate; dicrotophos, 3-dimethoxyphosphinoyloxy-N,N-dimethylisocrotonamide; dimethoate, O,O-dimethyl-S-methylcarbamoylmethyl phosphorodithioate; endosulfan, (1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenebismethylene)sulfite; fipronil, 5-amino-1-(2,6-dichloror-α,α,α-triflouro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile; glyphosate; imidacloprid, (EZ)-1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine; lambda-cyhalothrin, reaction product comprising equal quantities of (S-α-cyano-3-phenoxybenzyl (Z)-(1R,3R)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S,3S)-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate or of (S)-α-cyano-3-phenoxybenzyl (Z)-(1R)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate and (R)-α-cyano-3-phenoxybenzyl (Z)-(1S)-cis-3-(2-chloro-3,3,3-trifluoropropenyl)-2,2-dimethylcyclopropanecarboxylate; oxamyl, (EZ)-N,N-dimethyl-2-methylcarbamoyloxyimino-2-(methylthio)acetamide; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill #³ SEBEX; AESVI; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; redweed, Melochoia corchorifolia L. # MEOCO; cotton, Gossypium hirsutum L; cotton aphids, Aphis gossypii Glover; thrips, Frankliniella spp.

Additional index words: Aphids, herbicide–insecticide combinations, pesticide compatibility, thrips.

Abbreviations: DAT, days after treatment; POST, postemergence.

Multiple means of overcoming interspecific competition between transplanted cabbage and interseeded cover crops were studied in field trials conducted from 1995 to 2001. Cover crop species and time of seeding (1995 and 1996), use of supplemental nitrogen (1997 and 1998), and herbicide regulation (1999 and 2001) were evaluated with the objective of integrating soil-improving cover crops into cabbage production while facilitating weed suppression with minimal use of herbicides. Cabbage was cultivated at 10, 10 20, or 10 20 30 d after transplanting (DAT) with or without cover crops (hairy vetch, lana vetch, or oats) sown at the time of the last cultivation. Early interseeding (10 DAT) of all species significantly reduced cabbage yields. Both vetches could be sown 20 or 30 DAT without a yield penalty. However, weed suppression was not consistently greater than cultivation without cover crops. Spring oats were unacceptably competitive, even when sown 30 DAT in some years. With additional nitrogen, cabbage yields were consistently increased, but the increases were not directly related to decreased competition from either weeds or cover crops. The potential for herbicide regulation of cover crops to prevent cabbage yield losses could not be evaluated because cabbage yields were not reduced by cover crops in 1999 and 2001. Although interseeded crops did not generally provide significant in-season weed suppression compared with cultivation alone, the lack of yield penalty and the potential soil-improving qualities of legumes may justify interseeding hairy vetch at 20 DAT in an integrated system.

Nomenclature: Cabbage, Brassica oleracea L.; hairy vetch, Vicia villosa L.; lana vetch, Vicia dasycarpa L.; oats, Avena sativa L.

Additional index words: Cover crops, cultivation, interseeding, interspecific competition, living mulches, smother crops.

Abbreviation: DAT, days after transplanting.

Volunteer crops resistant to glyphosate and other herbicides pose a potential problem for Pacific Northwest (PNW) growers that rely on glyphosate for control of volunteer crops and weeds during fallow and before planting. Herbicides for control of volunteer herbicide-resistant wheat and canola in PNW conservation tillage systems were evaluated during 2000 and 2001 near Ralston, WA, and Moscow, ID. Paraquat diuron controlled glyphosate- and imidazolinone-resistant wheat ≥90%, and glyphosate controlled imidazolinone-resistant wheat 88 to 96% 14 d after treatment (DAT). Glyphosate- and imidazolinone-resistant wheat were controlled only 58 to 85% with quizalofop-P and clethodim 14 DAT. By 21 DAT, imidazolinone-resistant wheat control with clethodim and quizalofop-P was ≥93%, but the longer time period required for control to reach an acceptable level could increase disease and insect problems associated with volunteer wheat. Volunteer glyphosate-resistant canola was controlled 92 and 97% 14 DAT and 76 and 98% 21 DAT with paraquat and paraquat diuron, respectively. Treatments that contained glyphosate controlled imidazolinone- and glufosinate-resistant canola >84% 14 DAT. By 21 DAT, control of imidazolinone- and glufosinate-resistant canola was 94 to 98% with paraquat diuron and all glyphosate treatments, except glyphosate–isopropylamine salt (IPA) glufosinate (88 to 93%) and glyphosate-IPA paraquat (67 to 85%). In these studies, paraquat diuron was the best alternative to glyphosate for controlling volunteer herbicide-resistant wheat and canola.

Nomenclature: Clethodim; diuron; glufosinate; glyphosate; imidazolinone; paraquat; quizalofop-P; canola, Brassica napus L. ‘DKL 27-20’, ‘Phoenix’, ‘Pioneer 45A71’; wheat, Triticum aestivum L. ‘Bobwhite’, ‘FS-4 IR’.

Additional index words: Direct seeding, glufosinate resistant, glyphosate resistant, green-bridge, imidazolinone resistant.

Abbreviations: ACCase, acetyl coenzyme A carboxylase; DA, diammonium salt; DAT, days after treatment; HRC, herbicide-resistant crops; IPA, isopropylamine salt; PNW, Pacific Northwest.

Field studies were conducted near Sparr, FL, in 2001 and 2002 to evaluate the response of ‘Valencia 102’ grown for the green peanut market (or boiling peanut) to preemergence (PRE) and postemergence (POST) applications of herbicides registered for dry peanut production (roasted market). Green peanut exhibited excellent tolerance to most PRE and POST treatments. There was minimal injury (8%) from flumioxazin applications when evaluated early season in both years, and peanut quickly recovered. Norflurazon caused chlorosis to peanut foliage (23%) in both years. Yield reduction was observed in 2001 for flumioxazin (15%), metolachlor (20%), and norflurazon (41%) compared with the untreated control. However, there were no yield reductions for any of the PRE treatments in 2002. Bentazon paraquat early postemergence (EPOST) followed by (fb) 2,4-DB POST, bentazon paraquat EPOST fb clethodim POST, and imazapic EPOST caused ≤5% injury and had no effect on yield in either year.

Nomenclature: Bentazon; clethodim; 2,4-DB; flumioxazin; imazapic; metolachlor; norflurazon; paraquat; peanut, Arachis hypogaea L. ‘Valencia 102’.

Additional index words: Herbicide injury, chlorimuron, diclosulam, dry peanut, ethalfluralin, fluazifop, green peanut, imazethapyr, pryridate, sethoxydim.

Abbreviations: DAP, days after planting; EPOST, early postemergence; fb, followed by; POST, post-emergence; PRE, preemergence; WAE, weeks after emergence.

A 3-yr study was conducted on nine farms across southern Ontario to evaluate the risks and benefits of different approaches to weed management in corn and soybean. Weed control decisions were based on field scouting and recommendations from the Ontario version of HADSS™, the herbicide application decision support system. Treatments were selected to maximize profit (economic threshold approach) or to maximize yield (highest treatment efficacy). Reduced rates of the high efficacy treatment for each field also were included. Weed density before and after treatment, crop yields, weed seed return, and the effect of weed control decisions on weed density 1 yr after treatment were assessed. Crop yield varied among years and farms but was not affected by weed control treatment. Weed control at 28 d after treatment (DAT) was often lower and weed density, biomass, and seed production 70 DAT were often higher with the profit maximization approach compared with the yield maximization approach. However, weed density 1 yr later, after each cooperator had applied a general weed control program, did not vary significantly among the previous year's weed control treatments. Reduced rates of the high efficacy treatments did not lead to increased weed problems the next year, despite lower weed control and increased weed seed production in some years. During the 3 yr of the study, weed control costs with the profit maximization approach were approximately Can$45/ha less than with the yield maximization approach.

Nomenclature: Corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Additional index words: Economic threshold, net benefit, reduced rate, weed seed rain.

Abbreviations: DAT, days after treatment; HADSS, herbicide application decision support system; POST, postemergence.

Glyphosate-resistant canola was seeded at Vegreville, Alberta, in 1997 and 1999 and barley in rotation with the canola in 1998 at three seeding rates. The effects, at each crop seeding rate, of variable glyphosate (canola) and tralkoxydim plus bromoxynil plus MCPA (barley) rates on crop yield, net economic return and seed production by wild oat, wild mustard, and wild buckwheat, and the amount of weed seed in the soil seed bank was determined. Crop seeding rate influenced the response of canola and barley yield and weed seed production to herbicide rate. At the lowest crop seeding rates, yield responses tended to be parabolic with yields increasing up to one-half and three-quarters of the recommended herbicide rates and trends toward reduced yields at the full rates. This response was not evident at the higher crop seeding rates, where, in most cases the yield reached a maximum between one-half and the full recommended rate. The effects of the herbicides on weed seed production, especially at the lowest rate, were often superior at the higher crop seeding rates. The results indicate that seeding canola and barley at relatively high rates may reduce risk associated with lower crop yields and increased weed seed production at lower than recommended herbicide rates. However, the current cost of herbicide-resistant canola seed may preclude the adoption of this integrated weed management practice by growers.

Nomenclature: Bromoxynil; glyphosate; MCPA; tralkoxydim; wild buckwheat, Polygonum convolvulus L. #^3, POLCO; wild mustard, Sinapis arvensis L. #^3, SINAR; wild oat, Avena fatua L. #³ AVEFA; barley, Hordeum vulgare L. ‘Falcon’; canola, Brassica napus L. ‘Quest’.

Additional index words: Integrated weed management, reduced herbicide rates, soil seed bank.

The objective of this research was to assess the accuracy of remote sensing for detecting weed species in soybean based on two primary criteria: the presence or absence of weeds and the identification of individual weed species. Treatments included weeds (giant foxtail and velvetleaf) grown in monoculture or interseeded with soybean, bare ground, and weed-free soybean. Aerial multispectral digital images were collected at or near soybean canopy closure from two field sites in 2001. Weedy pixels (1.3 m²) were separated from weed-free soybean and bare ground with no more than 11% error, depending on the site. However, the classification of weed species varied between sites. At one site, velvetleaf and giant foxtail were classified with no more than 17% error, when monoculture and interseeded plots were combined. However, classification errors were as high as 39% for velvetleaf and 17% for giant foxtail at the other site. Our results support the idea that remote sensing has potential for weed detection in soybean, particularly when weed management systems do not require differentiation among weed species. Additional research is needed to characterize the effect of weed density or cover and crop–weed phenology on classification accuracies.

Nomenclature: Sethoxydim; giant foxtail, Setaria faberi Herrm. #³ SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH; soybean, Glycine max (L.) Merr. ‘Asgrow 2733’.

Additional index words: Precision farming, site-specific agriculture, weed maps.

Abbreviations: ACRE, Agronomy Center for Research and Education; DPAC, Davis-Purdue Agricultural Research Center; FLL, Fisher linear likelihood; MED, minimum Euclidian distance; SAM, spectral angle mapper; SSWM, site-specific weed management.

The effects of postemergence rimsulfuron, metribuzin, and adjuvant combinations on potato crop safety and weed control were evaluated in field studies conducted at the University of Idaho Aberdeen Research and Extension Center in 1999 and 2000. Rimsulfuron at 26 g ai/ha plus metribuzin at 0, 140, or 280 g ai/ha was combined with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO) in a 3 by 3 factorial with two controls. Under cool, cloudy conditions in 1999, initial ‘Russet Burbank’ potato injury was greater when metribuzin was included in the tank mixture than when rimsulfuron was applied alone, regardless of adjuvant. Under warmer conditions in 2000, however, adding MSO or COC to the tank mixture caused more injury than adding NIS. Rimsulfuron did not provide acceptable season-long common lambsquarters control in 1999 (76%) or in 2000 (88%), regardless of adjuvant. Rimsulfuron combined with metribuzin at 140 or 280 g/ha provided ≥95% common lambsquarters control both years, regardless of adjuvant. Among adjuvants, using MSO (1999 and 2000) or COC (2000) in the spray mixture improved common lambsquarters control compared with using NIS. Tuber yield and quality were not reduced as a result of metribuzin rate or adjuvant treatments either year compared with the weed-free control.

Nomenclature: Metribuzin; rimsulfuron; common lambsquarters, Chenopodium album L. #³ CHEAL; potato, Solanum tuberosum L. ‘Russet Burbank’.

Additional index words: Crop oil concentrate, crop safety, herbicide injury, methylated seed oil, nonionic surfactant.

Abbreviations: ALS, acetolactate synthase; COC, crop oil concentrate; MSO, methylated seed oil; NIS, nonionic surfactant; PNW, Pacific Northwest; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Two corn hybrids were evaluated to determine tolerance to foramsulfuron applications with and without the safener, isoxadifen-ethyl at five application timings. The corn hybrid N58D1 was more sensitive to foramsulfuron applications than N59Q9. Averaged across all application timings, the addition of isoxadifen-ethyl decreased corn injury of the more sensitive corn hybrid, N58D1. Foramsulfuron application timing had a significant effect on corn tolerance. The greatest corn injury generally occurred from foramsulfuron applications to V6 and V8 corn (visible collars). Foramsulfuron injury ranged between 9 and 37% from these two application timings, 7 d after treatment (DAT). By 21 DAT, corn generally recovered from foramsulfuron injury, and there were a few cases of reduced corn yield at the end of the season. Yield reductions and ear malformations were greatest at the Urbana location with both hybrids when foramsulfuron was applied to V12 corn. The addition of isoxadifen-ethyl alleviated ear malformations and increased corn yield from this application timing. Applications of foramsulfuron before V6 corn also were important in reducing corn injury and protecting yield. Therefore, when growers are using foramsulfuron for weed control, it will be important to select proper hybrids that are more tolerant as well as making applications before V6 corn.

Nomenclature: Foramsulfuron; corn, Zea mays L.

Additional index words: Application timing, crop tolerance, hybrid sensitivity.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence; WAP, weeks after planting.

Field, greenhouse, and laboratory studies were conducted to examine the potential for antagonism of postemergence graminicides when tank-mixed with cloransulam and to determine the role of herbicide absorption and translocation in observed antagonistic responses. Cloransulam antagonized annual grass control with aryloxyphenoxypropionate herbicides fluazifop-P, quizalofop, and the prepackaged formulation of fluazifop-P plus fenoxaprop. Cloransulam did not affect annual grass control with the cyclohexandiones clethodim and sethoxydim. In the greenhouse, increasing the rate of the graminicides was a more effective strategy for overcoming antagonism for quizalofop than for fluazifop-P or fluazifop-P plus fenoxaprop, and success was species dependent. Annual grass control with clethodim, sethoxydim, and glyphosate was not adversely affected by tank mixtures with cloransulam. Control of large rhizome johnsongrass was initially reduced when cloransulam was mixed with sethoxydim, fluazifop-P plus fenoxaprop, or quizalofop. By 6 wk after treatment, control of rhizome johnsongrass was antagonized only when cloransulam was mixed with sethoxydim. Rainfall within 1.5 h of application reduced johnsongrass control with glyphosate and sethoxydim but did not affect activity of the other herbicides. Absorption of ¹⁴C-fluazifop-P and ¹⁴C-quizalofop into broadleaf signalgrass was not affected by cloransulam 6 or 24 h after treatment. Translocation of ¹⁴C-fluazifop-P to broadleaf signalgrass shoot tissue above and below the treated leaf was decreased when fluazifop-P was combined with cloransulam. Translocation of quizalofop was not affected by cloransulam.

Nomenclature: Clethodim; cloransulam; fenoxaprop; fluazifop-P; glyphosate; quizalofop; sethoxydim; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; johnsongrass, Sorghum halepense (L.) Pers. # SORHA.

Additional index words: Absorption, annual grasses, antagonism, herbicide interactions, tank mixtures, translocation.

Abbreviations: APP, aryloxyphenoxypropionate; CHD, cyclohexanedione; HAT, hours after treatment; WAT, weeks after treatment.

Genetically engineered varieties of creeping bentgrass, resistant to glyphosate, have been developed. Studies were initiated in 2000 and 2001 to examine the relative competitive lateral spread of several transformed lines of creeping bentgrass, nontransformed controls, and cultivar standards. Five-centimeter-diameter vegetative plugs of creeping bentgrass were transplanted into a 1-yr-old stand of perennial ryegrass in Columbus, OH, and 10-yr-old bermudagrass or 10-yr-old St. Augustinegrass in Loxley, AL. Plots were watered to prevent moisture stress to either the bentgrass plugs or surrounding turf swards. Monthly average diameter of the creeping bentgrass was determined by measuring the longest spread and shortest spread. At the end of the experiment, no differences (P = 0.05) in lateral spread were observed between individual lines of transgenic bentgrass, standard cultivars, and nontransformed control lines. Lateral spread of transgenic lines was similar to or less than their nontransformed parent and the standard cultivars tested. Results indicate that glyphosate-resistant creeping bentgrass lines do not spread laterally more than nontransgenic lines. Therefore, if the glyphosate-resistant creeping bentgrass escaped into surrounding turfgrass swards, the potential for spread would not be greater than other creeping bentgrass cultivars currently in use.

Nomenclature: Glyphosate; bermudagrass, Cynodon dactylon L.; creeping bentgrass, Agrostis stolonifera L. syn. Agrostis palustris Huds.; perennial ryegrass, Lolium perenne L.; St. Augustinegrass, Stenotaphrum secondatum S. (Walt.) Kuntze.

Additional index words: Competition, genetically modified organism, GMO.

Studies were conducted during a 2-yr period measuring corn silage and grain yield and velvetleaf seed production in response to velvetleaf density. Velvetleaf densities of 0, 2, 5, 10, and 21 plants/m² were established in conventionally tilled corn. The percent corn yield reduction in response to velvetleaf density was similar for both years despite differences in total corn yield. Corn grain and silage yield responded differently to velvetleaf interference. Although both were adversely affected, silage yield reductions were twice that of grain at the low velvetleaf densities. A hyperbolic yield model predicted a maximum yield loss for corn silage and grain of 36 and 37% with incremental losses of 7 and 3%, respectively, as velvetleaf density increased. Velvetleaf seed production ranged from 2,256 to 4,844 seed/m² from the lowest to the highest density. This study demonstrates that corn silage yield is more sensitive than corn grain yield to velvetleaf interference, as well as how crop value plays an important role in determining economic thresholds. Finally, this research confirms the prolific nature of velvetleaf and shows that even at low densities, velvetleaf seed production could affect weed control decisions for many seasons to come.

Nomenclature: Velvetleaf, Abutilon theophrasti Medicus #³ ABUTH; corn, Zea mays L. ‘Pioneer 3140’.

Additional index words: Economic threshold, weed competition, weed interference, yield loss.

Abbreviations: ET, economic threshold.

Although the impact of Canada thistle (CT) on annual crop production is relatively well established, few investigations report on this weed's impact within perennial pastures. This field study assessed herbage yield losses within eight central Alberta pastures from 1999 to 2001. Each pasture was sampled in 1999 to quantify thistle and herbage biomass within 25 permanent plots. CT was controlled in 2000 and the response of vegetation measured in 2000 and 2001. Before removal, significant negative relationships (P < 0.05) between thistle abundance and herbage were noted at six sites. After thistle removal, herbage at several sites displayed positive responses. Both thistle density and biomass adequately predicted herbage yield loss. Yield losses due to CT can be substantial, peaking at 2 kg/ha for each kilogram of standing thistle biomass and 4.3 kg/ha with each additional thistle stem per square meter. Demonstrated yield losses were variable among sites however, likely due to factors such as heterogeneity in soils, available moisture, and variation in disturbance history or pasture vegetation composition. CT management in perennial pastures of western Canada may enhance pasture production, but further research is required to reliably predict the ability of pastures to respond.

Nomenclature: Canada thistle, Cirsium arvense (L.) Scop #³ CIRAR.

Additional index words: Forage biomass, pasture heterogeneity, precipitation, sward composition, weed density.

Abbreviations: CT, Canada thistle; N, nitrogen; OM, organic matter.

Field trials were established in orchardgrass and tall fescue grass pastures and hay fields during 2000 and 2001 to evaluate wild carrot, broadleaf plantain, buckhorn plantain, bladder campion, and yellow crownbeard response to a variety of herbicides and prepackaged herbicide combinations. Picloram plus 2,4-D at 0.23 plus 0.84 kg/ha and higher, triclopyr plus clopyralid at 0.96 plus 0.32 kg/ha and higher, and 2,4-D plus triclopyr at 2.20 plus 1.12 kg/ha provided greater than 84% wild carrot, broadleaf plantain, and buckhorn plantain control at 4 mo after treatment (MAT) in both years. Metsulfuron, picloram plus 2,4-D at 0.30 plus 1.12 kg/ha, and 2,4-D plus triclopyr at 2.20 plus 1.12 kg/ha provided from 56 to 61% control of bladder campion 4 MAT, which was the highest bladder campion control observed in these trials. Greater than 80% yellow crownbeard control was achieved during both years with picloram plus 2,4-D at 0.15 plus 0.56 kg/ha and higher and with triclopyr plus clopyralid at 0.96 plus 0.32 kg/ha and higher. Results from these experiments reveal that good broad-spectrum control of many biennial and perennial broadleaf weeds can be achieved with higher rates of the picloram plus 2,4-D and triclopyr plus clopyralid prepackaged combinations.

Nomenclature: Clopyralid; 2,4-D dimethylamine salt; metsulfuron; picloram; triclopyr; bladder campion, Silene vulgaris (Moench) Garcke #³ SILVU; broadleaf plantain, Plantago major L. # PLAMA; buckhorn plantain, Plantago lanceolata L. # PLALA; wild carrot, Daucus carota, L. # DAUCA; yellow crownbeard, Verbesina occidentalis (L.) Walter # VEEOC; orchardgrass, Dactylis glomerata L. ‘Benchmark’; tall fescue, Festuca arundinacea Schreb ‘Kentucky 31’.

Additional index words: Pasture weed control, perennial weed control.

Abbreviations: MAT, months after treatment.

Field experiments were conducted in 1998, 1999, and 2000 at two locations (Harrow and Ridgetown) in southwestern Ontario to determine the biologically effective rates (I₉₀) of a commercial formulation of flufenacet plus metribuzin for weed control and processing tomato tolerance. At the proposed label use rate, flufenacet plus metribuzin provided excellent (≥90%) early-season (22 to 29 d after planting) control of velvetleaf, good (80 to 89%) control of barnyardgrass and redroot pigweed, and fair (60 to 79%) control of common lambsquarters. Flufenacet plus metribuzin provided fair late-season (59 to 97 d after planting) control of redroot pigweed and common lambsquarters and poor (≤59%) control of barnyardgrass and velvetleaf. At Harrow and Ridgetown, I₉₀ values for early-season weed control ranged from 70 to 1,300 g ai/ha and 50 to 1,900 g ai/ha, respectively. Flufenacet plus metribuzin provided poor weed control at Ridgetown. This result was not attributable to higher weed density or particular weed species but may have been caused by lack of rainfall and too low application rates for the medium-textured soil type. It is estimated that flufenacet plus metribuzin at 1,400 g/ha can control green foxtail season-long, whereas barnyardgrass and common lambsquarters would require 1,900 g/ha. Season-long control of velvetleaf and redroot pigweed would require application rates of 3,200 and 7,100 g/ha, respectively. Only slight early-season crop injury was observed, which was not reflected in yields. Optimum yields of tomatoes were obtained at Harrow at rates lower or slightly higher than the registered rates for corn and soybean. Tomato yields were higher at Harrow than at Ridgetown, which may have been due to differences in soil texture. Tomatoes grown in a medium-textured (Ridgetown) soil appeared to be less competitive against weeds than those grown in a coarse-textured soil (Harrow).

Nomenclature: Flufenacet; metribuzin; barnyardgrass, Echinochloa crusgalli (L.) P. Beauv. #³ ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; green foxtail, Setaria viridis (L.) P. Beauv. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medik # ABUTH; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; tomato, Lycospersicon esculentum Mill. ‘Heinz 9478’.

Additional index words: Crop injury, preplant incorporated, specific herbicide rate, weed density.

Abbreviations: IWM, integrated weed management.

Alfalfa seed producers have a limited number of herbicide options to manage weed problems. MON-37500 (proposed name sulfosulfuron) is a sulfonylurea herbicide that controls dandelion and quackgrass, two common weeds in alfalfa fields. A study was conducted in two alfalfa fields at Valparaiso and Carrot River, Saskatchewan, Canada, from 1999 to 2001 to evaluate perennial weed control and alfalfa production responses with 0.5×, 1×, and 1.5× label-recommended rates of MON-37500 and also 2,4-DB and hexazinone. MON-37500 applied at the 1× and 1.5× rates at both locations reduced mid-May alfalfa vigor from 100% to between 80 and 90% and increased early-season control of dandelion and quackgrass by about 10 to 40 percentage units, when compared with other herbicide treatments. Improved weed control with 1× and 1.5× MON-37500 rates was sustained into mid-June only at Carrot River and was completely eliminated (100% vigor and 0% weed control), or almost so, by mid-July. MON-37500 did not control Canada thistle. Improved early-season weed control with the 1× MON-37500 rate apparently compensated for the loss of alfalfa vigor at Valparaiso, thus resulting in 27% (57 kg/ha) greater seed yield than with the other herbicide treatments. At Carrot River, hexazinone generally provided levels of weed control similar to MON-37500 but did not injure alfalfa. Consequently, alfalfa yields were highest and the proportion of dead (decaying) seed was least with this treatment. The 0.5× MON-37500 rate often resulted in inferior weed control relative to the 1× and 1.5× rates and never was among the herbicide treatments providing the greatest seed yield. Managing the residual activity of MON-37500 and its negative effect on alfalfa growth, especially at locations with soils having coarse texture and low organic matter content, represents the greatest challenge in making MON-37500 a reliable weed management tool for alfalfa seed producers.

Nomenclature: 2,4-DB; hexazinone; MON-37500, N-[[(4,6-dimethoxy-2-pyrimidinyl)-amino]-carbonyl]-2-(ethyl-sulfonyl)imidazo[1,2-a]pyridine-3-sulfonamide; Canada thistle, Cirsium arvense (L.) Scop. #³ CIRAR; dandelion, Taraxacum officinale Weber in Wiggers # TAROF; quackgrass, Elytrigia repens (L.) Neviski # AGRRE; alfalfa, Medicago sativa L.

Additional index words: Herbicide management, sulfonylurea, weed interference.

Trumpetcreeper, a deciduous, perennial vine found in the midwestern and southeastern United States, causes crop losses through direct competition and by crop entanglement, and control measures include both herbicides and tillage. The regenerative capacity of trumpetcreeper rootstocks of varying length and diameter when planted at different depths was evaluated in greenhouse experiments in Arkansas. Deeper placement of rootstocks delayed trumpetcreeper emergence but had no effect on shoot growth after emergence. Larger rootstock segments produced more shoots per plant and more total biomass production. However, smaller rootstock segments produced more shoots and total biomass per centimeter of rootstock. Overall, decreasing trumpetcreeper rootstock size will delay shoot emergence but may not result in increased long-term control.

Nomenclature: Trumpetcreeper, Campsis radicans (L.) Seem ex Bureau #³ CMIRA.

Additional index words: Perennial vine control, tillage, vegetative propagation.

Survival of horseweed in several glyphosate-tolerant cotton and soybean fields treated with glyphosate at recommended rates preplant and postemergence was observed in Mississippi and Tennessee in 2001 and 2002. Plants originating from seed collected from fields where horseweed escapes occurred in 2002 were grown in the greenhouse to the 5-leaf, 13- to 15-leaf, and 25- to 30-leaf growth stages and treated with the isopropylamine salt of glyphosate at 0, 0.025, 0.05, 0.1, 0.21, 0.42, 0.84, 1.68, 3.36, 6.72, and 13.44 kg ae/ha to determine if resistance to glyphosate existed in any biotype. All biotypes exhibited an 8- to 12-fold level of resistance to glyphosate when compared with a susceptible biotype. One resistant biotype from Mississippi was two- to fourfold more resistant than other resistant biotypes. Growth stage had little effect on level of glyphosate resistance. The glyphosate rate required to reduce biomass of glyphosate-resistant horseweed by 50% (GR₅₀) increased from 0.14 to 2.2 kg/ha as plant size increased from the 5-leaf to 25- to 30-leaf growth stage. The GR₅₀ rate for the susceptible biotype increased from 0.02 to 0.2 kg/ha glyphosate. These results demonstrate that the difficult-to-control biotypes were resistant to glyphosate, that resistant biotypes could survive glyphosate rates of up to 6.72 kg/ha, and that plant size affected both resistant and susceptible biotypes in a similar manner.

Nomenclature: Glyphosate; horseweed, Conyza canadensis (L.) Cronq. #³ ERICA; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Additional index words: Biomass reduction, glyphosate resistance, herbicide resistance, herbicide tolerance, weed resistance.

Abbreviations: DAT, day after treatment; POST, postemergence; WAT, week after treatment.

Four field studies were conducted at the Peanut Belt Research Station near Lewiston Woodville, NC, in 2000, 2001, and 2002 to evaluate crop tolerance, weed control, grain yield, and net returns in glyphosate-resistant corn with various herbicide systems. Preemergence (PRE) treatment options included no herbicide, atrazine at 1.12 kg ai/ha, or atrazine plus metolachlor at 1.68 kg ai/ha. Postemergence (POST) treatment options included glyphosate at 1.12 kg ai/ha as either the isopropylamine salt or the diammonium salt, either alone or in mixtures with mesotrione at 105 g ai/ha plus crop oil concentrate at 1% (v/v) or halosulfuron at 53 g ai/ha plus 0.25% (v/v) nonionic surfactant. All response variables were independent of glyphosate formulation. Addition of metolachlor to atrazine PRE improved large crabgrass and goosegrass control but did not always improve Texas panicum control. POST control of these annual grasses was similar with glyphosate alone or in mixture with halosulfuron or mesotrione. Glyphosate POST controlled common lambsquarters and common ragweed 89 and 93%, respectively. Glyphosate plus halosulfuron POST provided more effective yellow nutsedge control than glyphosate POST. Atrazine PRE or atrazine plus metolachlor PRE followed by any glyphosate POST treatment controlled Ipomoea spp. at least 93%. Glyphosate plus mesotrione in total POST systems always provided greater control of Ipomoea spp. than glyphosate alone. The highest yielding treatments always included glyphosate POST, either with or without a PRE herbicide treatment. Similarly, systems that included any glyphosate POST treatment had the highest net returns.

Nomenclature: Atrazine; glyphosate; halosulfuron; mesotrione; metolachlor; common lambsquarters, Chenopodium album L. #³ CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Texas panicum, Panicum texanum Buckl. # PANTE; yellow nutsedge, Cyperus esculentus L.; corn, Zea mays L. # ZEAMX.

Additional index words: Diammonium salt, isopropylamine salt, net returns.

Abbreviations: ALS, acetolactate synthase; DAT, days after early postemergence treatment; fb, followed by; GR, glyphosate-resistant; POST, postemergence; PRE, preemergence.

A 2-yr field study was conducted from 2002 to 2003 on a Dundee silt loam soil at the Southern Weed Science Research Unit Farm, Stoneville, MS (33°26′N latitude), to examine the effects of hairy vetch cover crop (hairy vetch killed at corn planting [HV-K], hairy vetch killed in a 38-cm-wide band centered over the crop row at corn planting [HV-B], hairy vetch left alive [HV-L], and no hairy vetch [NHV]) and glyphosate postemergence (broadcast, banded, and no herbicide) application on weed control and yield in glyphosate-resistant corn. Two applications of glyphosate at 0.84 kg ae/ha were applied 3 and 5 wk after planting (WAP) corn. Hairy vetch dry biomass was higher in HV-L (4,420 kg/ha) and HV-B (4,180 kg/ha) than in HV-K (1,960 kg/ha) plots at 7 WAP. Hairy vetch reduced densities of pitted morningglory, prickly sida, and yellow nutsedge in HV-B and HV-L compared with NHV plots, but hairy vetch had no effect on densities of barnyardgrass, johnsongrass, and large crabgrass at 7 WAP regardless of desiccation. Total weed dry biomass at 7 WAP was lower in HV-B and HV-L than in HV-K and NHV plots. Corn yield was higher in HV-K (10,280 kg/ha) than in HV-B (9,440 kg/ha) and HV-L (9,100 kg/ha), and yields were similar between HV-K and NHV (9,960 kg/ha). Glyphosate applied broadcast resulted in the highest corn yield (11,300 kg/ha) compared with a banded application (10,160 kg/ha). These findings indicate that hairy vetch cover crop has the potential for reducing the density of certain weed species in glyphosate-resistant corn production systems; however, optimum weed control and higher yield were obtained when glyphosate was used.

Nomenclature: Glyphosate; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; hairy vetch, Vicia villosa Roth # VICVI; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; large crabgrass, Digitaria sanguinalis (L.) Scop # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. ‘AG RX 738RR’, ‘DKC 69-72RR’.

Additional index words: Cover crop, glyphosate, integrated weed management, mulch, transgenic corn, weed biomass, weed density.

Abbreviations: HV-B, hairy vetch killed in a 38-cm-wide band centered over the crop row at corn planting; HV-K, hairy vetch killed at corn planting; HV-L, hairy vetch left alive; NHV, no hairy vetch; POST, postemergence; WAP, weeks after planting.

Soft red winter wheat response to the herbicides AE F130060 00 plus AE F115008 00 applied alone or with the safener AE F107892 at the three-leaf, two-tiller, and six-tiller growth stages was determined in a field experiment in North Carolina. AE F130060 00 at 25 g ai/ha plus AE F115008 00 at 5 g ai/ha, twice the anticipated use rate, applied with safener injured wheat 9% but did not affect grain yield, grain test weight, number of spikes, number of kernels per spike, or kernel weight. Results were similar with safener at herbicide–safener ratios of 1:1 and 1:3 regardless of the wheat growth stage at application. Without the safener, AE F130060 00 plus AE F115008 00 applied at the three-leaf, two-tiller, and six-tiller growth stages injured wheat an average of 27% and reduced grain yields 5, 5, and 11%, respectively. Yield losses were attributed to reduced numbers of kernels per spike. AE F130060 00 at 12.5 g/ha plus AE F115008 00 at 2.5 g/ha plus AE F107892 at 15 g ai/ha did not affect grain yield or yield components.

Nomenclature: AE F107892 (proposed name, mefenpyr-diethyl), 1-(2,4-dichlorophenyl)-4,5-dihydro-5-methyl-1H-pyrazole-3,5-dicarboxylic acid; AE F115008 00 (proposed name, iodosulfuron-methyl-sodium), 4-iodo-2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid methyl ester; AE F130060 00 (proposed name mesosulfuron-methyl), methyl 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-4-[[(methylsulfonyl)amino]methyl]benzoate; wheat, Triticum aestivum L. ‘Coker 9704’.

Additional index words: Herbicide injury, wheat yield, yield components.

Abbreviations: FGS, feekes growth stage; POST, postemergence; WAT, weeks after treatment.

Research was conducted in winter of 2000 and spring of 2001 to determine the extent of simazine-resistant annual bluegrass in Mississippi. Samples of annual bluegrass seed or mature plants were collected from 71 locations across the state and grown in the greenhouse. Four weeks after treatment with 22.4 kg ai/ha simazine (10× rate), samples from 31 of 71 locations (30 golf courses and one nongolf course) evaluated in the greenhouse had simazine-resistant annual bluegrass plants. Thus, 43% of the golf courses tested in the greenhouse had triazine-resistant annual bluegrass present. When natural field populations were treated with an equivalent simazine rate, simazine-resistant annual bluegrass plants were observed in 90% of the sites found to be resistant in the greenhouse screen.

Nomenclature: Simazine; triazine; annual bluegrass, Poa annua L. #³ POAAN.

Additional index words: Herbicide resistance, triazine.

Abbreviations: WAT, weeks after treatment.

‘Russet Burbank’ potato tolerance to dimethenamid-p applied preemergence at 0.7, 1.4, or 2.9 kg ai/ha was assessed in field studies conducted at Aberdeen, ID and Ontario, OR. Although crop injury was evident approximately 2 wk after treatment, most injury had diminished by row closure 2- to 3-wk later. Initial injury did not translate to yield loss and U.S. No. 1 and total tuber yields in dimethenamid-p–treated plots were similar to yields in the untreated, weed-free control.

Nomenclature: Dimethenamid-p; potato, Solanum tuberosum L. ‘Russet Burbank’.

Additional index words: Crop safety, crop tolerance, herbicide injury.

Abbreviations: EPTC, S-ethyl dipropyl carbamothioate; PNW, Pacific Northwest; WAT, weeks after treatment.

A 3-yr study was conducted in Wheatland County, Alberta to determine if agronomic practices of growers influenced the occurrence of herbicide resistance in wild oat. Wild oat seeds were collected in 33 fields in 1997 and in 31 fields in each of 1998 and 1999 (one field per grower). Seedlings were screened for resistance to two acetyl-CoA carboxylase (ACCase) inhibitors, imazamethabenz, an acetolactate synthase (ALS) inhibitor, and triallate, a thiocarbamate herbicide. A questionnaire on herbicide resistance awareness and management practices was completed by each grower. Both ACCase and ALS inhibitor resistance in wild oat were linked to a lack of crop rotation diversity. In addition, ALS inhibitor–resistant wild oat was associated with conservation-tillage systems and recent use of herbicides with that mode of action. Results of this study suggest that timely tillage and inclusion of fall-seeded and perennial forage crops in rotations will effectively slow the selection of resistance in this grass species.

Nomenclature: Imazamethabenz; triallate; wild oat, Avena fatua L. #³ AVEFA.

Additional index words: Herbicide rotation, integrated weed management, survey, fenoxaprop, sethoxydim.

Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase.

A general life cycle model was modified to demonstrate how agronomic practices and weed biology factors affect the rate of appearance of herbicide-resistant downy brome, jointed goatgrass, and wild oat in Pacific Northwest wheat cropping systems. The model suggests herbicide rotation strategies for cropping systems that include imidazolinone-resistant wheat as a weed management tool. Simulation of continuous annual imidazolinone-resistant winter wheat and imazamox herbicide use resulted in the resistant soil seed banks of downy brome, jointed goatgrass, and wild oat surpassing their susceptible soil seed banks in 5, 7, and 10 yr, respectively. Reducing the initial seed bank density of downy brome before beginning a rotation that includes imidazolinone-resistant winter wheat reduces the likelihood of selecting for herbicide-resistant biotypes. The best simulated management option for reducing the total jointed goatgrass soil seed bank in low-precipitation areas is an imidazolinone-resistant winter wheat–fallow rotation. Rotations that include winter and spring crops and rotations that include non–group 2 herbicides minimize herbicide resistance selection pressure and reduce the wild oat soil seed bank.

Nomenclature: Imazamox; downy brome, Bromus tectorum L. # BROTE; jointed goatgrass, Aegilops cylindrica Host #3 AEGCY; wild oat, Avena fatua L. # AVEFA; winter wheat, Triticum aestivum L. Clearfield™.

Additional index words: Crop rotation, population model, resistance management.

Abbreviations: ALS, acetolactate synthase; PNW, Pacific Northwest.