Many herbicides that control broadleaf weeds in wheat can antagonize grass herbicide efficacy, resulting in less grain yield due to competition. Also, the broadleaf herbicide carfentrazone-ethyl can injure wheat, leading to less grain yield because of physiological response. Experiments were conducted to evaluate carfentrazone-ethyl antagonism of fenoxaprop-ethyl, tralkoxydim, clodinafop-propargyl, imazamethabenz, and flucarbazone-sodium and injury to wheat with tank mixes of carfentrazone-ethyl plus each grass herbicide or thifensulfuron, tribenuron, metsulfuron, or imazamox. Carfentrazone-ethyl did not adversely affect control of wild oat or yellow foxtail by grass herbicides in wheat. Carfentrazone-ethyl alone caused 21% wheat injury 3 d after treatment. Adding flucarbazone-sodium to carfentrazone-ethyl resulted in the least wheat injury among treatments that included carfentrazone-ethyl. Fenoxaprop-P-ethyl or clodinafop-propargyl with carfentrazone-ethyl also resulted in less wheat injury compared with carfentrazone-ethyl alone, which was attributed to formulation safeners. Sulfonylurea herbicides provided safening of carfentrazone-ethyl similar to flucarbazone-sodium, while imidazolinones did not alleviate injury. Tralkoxydim plus carfentrazone-ethyl gave 28% wheat injury compared with 21% from carfentrazone-ethyl alone. Wheat injury was no longer visible by 20 d after treatment, and wheat yield was not affected by carfentrazone-ethyl injury when wild oat and yellow foxtail were present or controlled with herbicide.

Nomenclature: Carfentrazone-ethyl; clodinafop-propargyl; fenoxaprop-P-ethyl; flucarbazone-sodium; tralkoxydim; yellow foxtail, Setaria glauca (L.) Beauv. #³ SETLU; wild oat, Avena fatua L. # AVEFA; wheat, Triticum aestivum L. ‘Alsen’, ‘ND722’, ‘Oxen’.

Additional index words: Antagonism, crop injury, safening with herbicides, imazamethabenz, imazamox, thifensulfuron, tribenuron, metsulfuron.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); COC, crop oil concentrate; DAT, days after treatment; MSO, methylated seed oil; NIS, nonionic surfactant; PO, petroleum oil; UAN, urea and ammonium nitrate solution.

Composted manure produced in deep-bedded hoop structures constitutes a source of nutrients and organic materials that can influence crop and weed emergence, growth, competitive interactions, and soil physical properties. The impact of composted swine manure on corn, soybean, winter wheat, velvetleaf, giant foxtail, and common waterhemp emergence and early growth were compared at compost rates of 0, 8, 16, or 24 Mg C/ha. Compost amendment had no effect on crop emergence but did reduce weed emergence. Inhibition of seedling emergence ranged between 15 and 57% for giant foxtail, 0 and 23% for velvetleaf, and 16 and 76% for common waterhemp. Soil amendment enhanced weed growth but not crop growth. A response surface regression analysis indicated that, while large-seeded crops have constant relative growth rates, small-seeded weed species increase their relative growth rates with compost amendment (P < 0.0001, r² = 0.5252).

Nomenclature: Common waterhemp, Amaranthus rudis Sauer #³ AMATA; corn, Zea mays L. ‘Pioneer 3563’; giant foxtail, Setaria faberi SETFA Herm.; soybean, Glycine max (L.) Merr. ‘Pioneer 92B84’; velvetleaf, Abutilon theophrasti ABUTH Medicus; winter wheat, Triticum aestivum L. ‘Arapahoe’.

Additional index words: Compost amendment, relative growth rate, germination inhibition, organic amendment, seedling emergence, soil quality.

Abbreviations: EI%, percentage emergence inhibition; MTE, mean time of emergence; RGR, relative growth rate; VOA, volatile organic acids.

Wild oat is the most serious grass weed in Argentine barley crops and its control has concentrated on herbicide strategies. Increasing crop density could be an effective strategy to reduce the effect of wild oat on barley yield. However, limited research has been conducted to evaluate the effect of crop density on the competitive balance between barley and spontaneous populations of wild oat. A field experiment was conducted in 1992, 1993, and 1999, to study the effect of spontaneous populations of wild oat on barley sown at densities of 160, 220, and 280 plants/m². Wild oat density averaged 84 plants/m². Wild oat biomass increased linearly with weed density in all treatments but was reduced by increasing barley seeding rates. Barley biomass and yield were not affected by wild oat at high crop sowing densities, but for the low and medium barley densities, yield loss was almost 25% when 70 wild oat plants/m² were established. Barley yield loss was mostly related to competition from the early emerged wild oat. The relationship between yield losses and wild oat density was equally significant when the whole population or only early emerged individuals of the weed were considered.

Nomenclature: Wild oat, Avena fatua L. #³ AVEFA; barley, Hordeum vulgare L.

Additional index words: Wild oat interference in barley, integrated wild oat management, seeding rates of barley.

Wide-spread planting of glyphosate-resistant (GR) crops in the United States and glyphosate patent expiration has led to a proliferation of glyphosate products. Growers have questioned their advisors on efficacy and crop tolerance of the many products available. Field experiments were conducted to evaluate eight glyphosate products in 2002 and ten in 2003, representing isopropylamine, diammonium, and potassium salts, applied POST and postemergence-directed (PDIR) at 630 and 1,680 g ae/ha for GR corn and GR cotton tolerance and weed control. There were no differences among products for control of six annual grass and 10 annual broadleaf weed species. No injury to corn from any glyphosate product at 630 or 1,680 g/ha or to cotton from 630 g/ha was noted at any of seven locations. ClearOut 41 Plus™, an isopropylamine salt of glyphosate, and Roundup WEATHERMAX™, a potassium salt of glyphosate, applied POST at 1,680 g/ha injured cotton 27 to 30% and 10 to 17%, respectively, at 3 of 7 locations. No cotton injury was noted with Glyfos®, Glyfos® X-TRA, Glyphomax™, Gly Star™ Original, Roundup Original™, Roundup UltraMAX®, Touchdown®, or Touchdown Total™. No differences were noted among glyphosate products or between rates for corn or cotton yield or cotton fiber properties.

Nomenclature: Glyphosate; corn, Zea mays L. ‘DK687’, ‘DKC 69-71’; cotton, Gossypium hirsutum L. ‘DP 458 B/RR’, ‘ST 4892BR’.

Additional index words: ClearOut 41 Plus™, crop tolerance, diammonium salt of glyphosate, Glyfos®, Glyfos® X-TRA, Glyphomax™, Gly Star™ Original, isopropylamine salt of glyphosate, potassium salt of glyphosate, Roundup Original™, Roundup UltraMAX®, Roundup WEATHERMAX™, Touchdown®, Touchdown Total™, weed control.

Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; GR, glyphosate-resistant; PDIR, postemergence-directed; PEP, phosphoenolpyruvate; WAP, wk after postemergence application; WAP1, wk after first postemergence application; WAP2, wk after second postemergence application; WAPD, wk after postemergence-directed application.

Experiments were conducted in North Carolina during 2002 and 2003 to evaluate entireleaf morningglory control by 2,4-DB applied alone or with seven fungicides. In a separate group of experiments, tall morningglory control by 2,4-DB was evaluated when applied in four-way mixtures with the following: the fungicides azoxystrobin, chlorothalonil, pyraclostrobin, or tebuconazole; the insecticide lambda-cyhalothrin; and the foliar fertilizer disodium octaborate or the plant growth regulator (PGR) prohexadione calcium plus urea ammonium nitrate. Pyraclostrobin, but not azoxystrobin, boscalid, chlorothalonil, fluazinam, propiconazole plus trifloxystrobin, or tebuconazole, reduced entireleaf morningglory control by 2,4-DB. Mixtures of fungicides, insecticides, and foliar fertilizer/ PGR did not affect tall morningglory control by 2,4-DB. Placing artificial morningglory in the peanut canopy when fungicides were applied did not intercept enough fungicide to increase peanut defoliation by early leaf spot and web blotch or reduce pod yield compared with fungicide applied without artificial morningglory.

Nomenclature: 2,4-DB; azoxystrobin; boscalid; chlorothalonil; fluazinam; lambda-cyhalothrin; prohexadione calcium; propiconazole; pyraclostrobin; tebuconazole; trifloxystrobin; entireleaf morningglory, Ipomoea hederacaea var integriuscula Gray #³ IPOHG; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; early leaf spot, Cercospora arachidicola S. Hori; web blotch, Phoma arachidicola (Marsas et al.); peanut, Arachis hypogaea L. ‘NC-V 11’, ‘VA 98R’.

Additional index words: Fungicide deposition, pesticide interactions, weed interference.

Abbreviations: PGR, plant growth regulator; UAN, urea ammonium nitrate.

Purple nutsedge management with herbicides (halosulfuron, imazaquin, MSMA, S-metolachlor, and sulfentrazone) and mowing was investigated in a bare ground homogenous purple nutsedge field site. Mowing at 5 cm increased control of purple nutsedge by 6% compared to not mowing. Sequential applications of halosulfuron, MSMA, and sulfentrazone provided at least 80% control of purple nutsedge shoots, whereas imazaquin controlled purple nutsedge shoots less than 65%. All herbicide treatments reduced purple nutsedge total and viable tuber densities at least 40%. S-metolachlor PRE reduced total and viable tuber densities 65 and 69%, respectively. Sequential applications of sulfentrazone or MSMA reduced total and viable tubers 80%. Early postemergence (EPOST) or EPOST followed by late-postemergence applications of halosulfuron and imazaquin reduced total and viable tuber densities 52 and 59%, respectively. Data indicate that S-metolachlor PRE and sequential applications of MSMA and sulfentrazone may be viable treatments for control of purple nutsedge shoots and tubers.

Nomenclature: Halosulfuron; imazaquin; MSMA; S-metolachlor; sulfentrazone; purple nutsedge, Cyperus rotundus L. #³ CYPRO.

Additional index words: Purple nutsedge control, purple nutsedge tuber viability.

Abbreviations: EPOST, early postemergence; LPOST, late-postemergence; WALP, weeks after late-postemergence; WAT, weeks after treatment.

Yellow starthistle is an annual that is dependent on achene production, dispersal, and germination for stand renewal. Our purpose in this study was to determine the temperature relations for germination of achenes of this species. Germination temperature profiles were developed for achenes of yellow starthistle collected from 15 sites in California, Nevada, and Oregon. Each profile consisted of achene germination at 55 constant or alternating temperatures from 0 through 40 C. A total of 85 germination temperature profiles were developed by using the germination data to construct quadratic response surfaces through regression analysis. For most profiles, germination occurred at all the temperature regimes except a constant 40 C. This includes a constant 0 C and 0 alternating with 40 C. Rarely, there was no germination at 35 C and 35 C alternating with 40 C. The only evidence of afterripening requirements for achenes of yellow starthistle that we noted occurred at very cold temperature regimes. At those temperatures, the germination of dark-colored achenes without pappus increased 3 mo after harvest, and decreased for light-colored achenes with a pappus. No single temperature regime always supported optimum germination when all the profiles were combined. The most frequent optima was 2/20 C. Comparing all profiles for the Davis, CA, accession, there were 5 regimes (5 and 10 C cold periods alternating with 15 through 25 C warm periods) that always supported optimum germination. Light-colored achenes with pappus tended to have optimal germination at colder temperatures, and the dark-colored achenes at higher temperatures when seeds were tested immediately after harvest.

Nomenclature: Alfalfa, Medicago sativa L. #³ MEDSA; tocalote, Centaurea melitensis L.; yellow starthistle, Centaurea solstitialis L. # CENSO.

Additional index words: Seedbed ecology, seedbed temperatures, optimum germination, invasive species.

Herbicides commonly used to control Cyperus spp. are not completely effective against Kyllinga spp. Field trials were conducted on North Carolina golf courses to evaluate green and false-green kyllinga control at fairway and rough golf course mowing heights. Treatments included single and sequential applications of bentazon (1.12 kg ai/ha), halosulfuron (0.07 kg/ha), MSMA (2.24 kg/ ha), and trifloxysulfuron (0.03 kg/ha); imazaquin (0.56 kg/ha) with and without MSMA; and two rates of sulfentrazone (0.42 and 0.56 kg/ha). Green or false-green kyllinga control was equivalent at fairway and rough mowing heights. Halosulfuron applied sequentially, imazaquin with and without MSMA, and trifloxysulfuron applied singly or sequentially, controlled green and false-green kyllinga 89 to 99% 10 wk after initial treatment (WAIT). However, Kyllinga spp. control decreased over the course of the study regardless of herbicide treatment. By one year after treatment (YAIT), bentazon or MSMA alone controlled green or false-green kyllinga 50% or less. No difference was observed in green or false-green kyllinga control between imazaquin vs. imazaquin plus MSMA, sulfentrazone 0.42 vs. 0.56 kg/ha, or trifloxysulfuron one vs. two applications at any rating date. Green kyllinga was seemingly more difficult to control than false-green kyllinga. Sequential applications of bentazon and MSMA, single applications of halosulfuron, sulfentrazone applied at 0.42 and 0.56 kg/ha, and single and sequential applications of trifloxysulfuron controlled false-green kyllinga at least 10% greater than green kyllinga at 1 YAIT. Further research is needed to assess the potential variation among Cyperus and Kyllinga spp. response to herbicides.

Nomenclature: Bentazon, halosulfuron, imazaquin, monosodium methanearsonate (MSMA), sulfentrazone, trifloxysulfuron; bermudagrass, Cynodon spp.; false-green kyllinga, Kyllinga gracillima L.; green kyllinga, Kyllinga brevifolia Rottb. #³ KYLBR.

Additional index words: Mowing height, turfgrass management.

Abbreviations: WAIT, weeks after initial treatment; YAIT, year after initial treatment.

Field studies were conducted over 3 yr at two locations to evaluate the effects of glyphosate rate and application timing on barnyardgrass control, seed production, seed viability, and seedbank density the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when barnyardgrass was at the two-, four-, or six-leaf stage of growth. Visual estimates of percent control increased whereas density, dry weight, seed production, and seedbank density the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the rate of glyphosate from 450 to 900 g/ha (registered rate) had no further effect on any measured parameter. Seed viability was not affected by glyphosate rate nor application timing. Corn yield declined only at a glyphosate rate of 225 g/ha and below. Barnyardgrass control improved as application was delayed to the six-leaf stage because this weed had an extended period of emergence. There was no interaction between glyphosate rate and application timing on any parameter, and yield was not affected by glyphosate-application timing. The use of extremely low glyphosate rates (112 or 225 g/ha) resulted in reduced corn yields, increased barnyardgrass seed production, and seedbank density the year after application.

Nomenclature: Glyphosate; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; corn, Zea mays L. ‘PrideG4286’, ‘DeKalb 493RR’.

Additional index words: Reduced rates, weed control, weed seed production, weed seedbank density.

Abbreviations: DAA, days after application.

A population of common waterhemp in northeast Kansas was confirmed resistant to protoporphyrinogen oxidase (protox)-inhibiting herbicides in 2001. In 2002, seeds were collected from 28 sites in a 16-km radius surrounding the site where resistance was confirmed to determine the extent of protox resistance in common waterhemp populations throughout the area. In addition, common waterhemp response to acetolactate synthase (ALS)-inhibiting herbicides and glyphosate was determined. At least one common waterhemp plant among the 48 plants tested from each of 10 sites was acifluorfen-resistant. These sites were randomly scattered throughout the sampling area, and resistance may have resulted from seed or pollen movement or independent development. Acifluorfen-resistant common waterhemp plants were initially injured by acifluorfen, but plants began recovering from injury within 14 days after treatment (DAT). All sites contained at least two common waterhemp plants with imazethapyr resistance, whereas plants from all sites were susceptible to glyphosate. Because acifluorfen- and imazethapyr-resistant common waterhemp populations are found in northeastern Kansas, protox-inhibiting and ALS-inhibiting herbicides may not provide common waterhemp control.

Nomenclature: acifluorfen-methyl; glyphosate; imazethapyr; common waterhemp, Amaranthus rudis Sauer, #³ AMATA.

Additional index word: Herbicide resistance.

Abbreviations: ALS, acetolactate synthase [E.C. 2.2.1.6]; DAT, days after treatment; protox, protoporphyrinogen oxidase [E.C. 1.3.3.4].

Farmer observations and previous studies indicated that reductions in soybean yield caused by the soybean cyst nematode (SCN) are greater when other stresses, biotic or abiotic, are present. Also, it has been reported that the effect of SCN on soybean growth depended on factors such as soil pH, soil texture, and herbicides. Although postemergence herbicides may adversely affect soybean metabolism, acifluorfen can reduce SCN infection. The objective of the present study was to determine the main and interactive effects of SCN egg population density (SCN_D), soil pH, soil texture, and the application of the herbicides acifluorfen, glyphosate, and imazethapyr on early soybean growth. Greenhouse studies assessed different combinations of these factors for 65 d after planting. No interactions were observed for any of the main effects. Soil pH and texture did not affect soybean growth. SCN_D was the only main effect that explained soybean growth reductions. The effect of SCN_D on soybean growth was exhibited as 15–50% decreases of leaf area index (LAI) and dry weight in all cases, but reductions in plant height also were observed. No relationship between SCN_D and the number of SCN eggs recovered at the end of the experiment was observed. Herbicides did not reduce soybean growth, although acifluorfen consistently caused the highest soybean injury reaching 18–20% from 1–14 days after application (DAA). At 50 DAA, acifluorfen injury was negligible, and soybean LAI and dry weight did not differ from the nontreated control. These results indicated that the effect of SCN on soybean growth was not directly affected by the other evaluated main effects. Therefore, trends observed in the field that suggested interactions between those factors are likely the result of other factors not considered in the present study or to more complex relationships between factors analyzed in the present study and other elements present in the field.

Nomenclature: Acifluorfen, glyphosate, imazethapyr; soybean; soybean cyst nematode, Heterodera glycines Ichinoche.

Additional index words: Herbicide injury, nematode infection.

Abbreviations: AMS, ammonium sulfate; COC, crop oil concentrate; DAA, days after application; DAP, days after planting; LAI, leaf area index: MSO, methylated seed oil; PPFD, photosynthetic photon flux density; SCN, soybean cyst nematode; SCN_D, SCN egg population density.

Field trials were conducted at five sites from 2001 through 2003 to determine the influence on sugarbeet and weeds of repeated broadcast and banded reduced rates of desmedipham plus phenmedipham, triflusulfuron, and clopyralid in combination with either 1.5 or 3% v/v methylated seed oil (MSO). Desmedipham plus phenmedipham, triflusulfuron, and clopyralid were applied POST three times at 5 to 7 d intervals at either 25, 50, 75, or 100% of a 180 plus 180 plus 18 plus 100 g ai/ha dosage (full rate). When averaged over all herbicide rates, crop injury was 6% greater, but common lambsquarters control was 5% higher, and crop yield was 15% greater with broadcast compared with banded herbicide application. In most situations, adding MSO at 3% rather than 1.5% did not improve weed control. Sugarbeet injury was lowest (11%) and the average weed control was 86% when herbicide rates (with 1.5% MSO) were 25% of the full rate (microrate). Applying an herbicide rate (with 1.5% MSO) that was 50% of the full rate (half rate) increased crop injury from 11% with the microrate to 18% with the half rate and elevated average weed control from 86% with the microrate to 92% with the half rate. Common lambsquarters control increased from 81% with the microrate to 89% with the half rate. Sugarbeet root yield was 23 t/ha when no herbicide was used, 48 t/ha with the microrate, and 49 t/ha with the half rate compared with 54 t/ha when the full rate was applied without MSO. Increasing herbicide rates to 75% of the full rate (three-quarter rate) (with 1.5% MSO) increased crop injury to 27% and average weed control to 96%. Applying 1.5% MSO to the full rate increased crop injury to 35% with no improvement in average weed control over that achieved with the full rate without MSO.

Nomenclature: Clopyralid; desmedipham; phenmedipham; triflusulfuron; common lambsquarters, Chenopodium album L. #³ CHEAL; sugarbeet, Beta vulgaris L. ‘Beta 1775’, ‘Beta 4546’, ‘HM1639RZ’.

Additional index words: Adjuvants, crop tolerance, crop yield.

Abbreviations: DAT, days after treatment; full rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 180 plus 180 plus 18 plus 100 g/ha; half rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 90 plus 90 plus 9 plus 50 g/ha; microrate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 45 plus 45 plus 4.5 plus 25 g/ha; MSO, methylated seed oil; three-quarters rate, desmedipham plus phenmedipham, triflusulfuron, and clopyralid at 135 plus 135 plus 13.5 plus 75 g/ha.

Partial seed retention line #23(‘PSR23’) cuphea is a hybrid of Cuphea viscosissima × C. lanceolata. It is a new, spring-planted, annual, potential oilseed crop that is highly susceptible to interference by weeds because of its slow growth during spring and early summer. Grass weeds are controlled easily in this broadleaf crop, but broadleaf weeds are an appreciable problem. Consequently, several broadleaf herbicides were screened for tolerance by ‘PSR23’ cuphea. Broadleaf herbicides to which cuphea showed tolerance in a spray cabinet and a greenhouse were tested in a field setting for 2 yr. Field tolerance was considered as absence of negative impact (P > 0.05) both years to any of four measured traits: overall vigor, dry weight, stand density, and time to anthesis. Cuphea showed tolerance in the field to three soil-applied herbicides (ethalfluralin, isoxaflutole, and trifluralin) and one postemergence herbicide (mesotrione). A few combinations of soil-applied and postemergence herbicides did not damage cuphea. These combinations were ethalfluralin followed by (fb) mesotrione, isoxaflutole fb imazethapyr, and isoxaflutole fb mesotrione. Availability of these herbicides for use in cuphea production may facilitate the domestication and acceptance of this new crop.

Nomenclature: ‘PSR23’ cuphea, Cuphea viscosissima Jacq. × C. lanceolata f. silenoides W. T. Aiton.

Additional index words: Capric acid, ethalfluralin, isoxaflutole, imazethapyr, lauric acid, mesotrione, oilseed, PSR23, trifluralin.

Abbreviations: fb, followed by; MCFA, medium chain fatty acid; PA, plant-applied; PPI, preplant incorporated; ‘PSR23’, partial seed retention line #23; SA, soil-applied.

KIH-485 is an experimental herbicide being evaluated for preemergence weed control in corn. Field experiments were conducted in Burleson County, Texas, in 2003 and 2004 to compare weed control, corn tolerance, and corn yield with various rates of KIH-485 or S-metolachlor. Each herbicide was applied in single preemergence applications at four rates, or in combination with atrazine. KIH-485 at 500 g ai/ha provided better Texas panicum control than S-metolachlor by 9 WAT. KIH-485 or S-metolachlor treatments controlled Palmer amaranth at least 91% at all evaluation dates. In 2003, no other treatment controlled velvetleaf better than 500 g/ha KIH-485. The following year, all KIH-485 rates above 125 g/ha controlled velvetleaf better than any rate of S-metolachlor alone. Moreover, KIH-485 controlled all weed species as good as or better than S-metolachlor plus atrazine, regardless of KIH-485 rate. There was no significant corn injury observed, and grain yield reflected the effects of weed control.

Nomenclature: Atrazine; KIH-485, 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylsulfonyl]-4,5-dihydro-5,5-dimethylisoxazole; metolachlor; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats.; #³ AMAPA; Texas panicum, Panicum texanum Buckl., # PANTE; velvetleaf, Abutilon theophrasti Medicus, # ABUTH; corn, Zea mays L. #³ ZEAMA.

Additional Index Words: Corn weed control, experimental herbicide, preemergence.

Abbreviations: WAT, weeks after treatment.

Field studies were conducted near Marianna, FL during 1999 and 2000 to evaluate weed control and peanut response to PPI treatments of diclosulam alone, PRE treatments of flumioxazin alone, and in systems with POST commercial standard herbicides. Diclosulam and flumioxazin alone did not control sicklepod. Paraquat plus bentazon plus 2,4-DB applied early POST fb chlorimuron plus 2,4-DB or imazapic controlled sicklepod and pitted morningglory at least 83%. These treatments were equal to or greater than diclosulam or flumioxazin with or without paraquat plus bentazon plus 2,4-DB, or the same system fb 2,4-DB mid POST. Peanut yield was similar when treated with diclosulam or flumioxazin fb the standard early POST (EPOST) system, flumioxazin alone, or imazapic alone. Peanut treated with diclosulam alone or paraquat plus bentazon plus 2,4-DB fb 2,4-DB yielded lower than other treatments because of late-emerging Florida beggarweed. Peanut treated with chlorimuron, regardless of which soil-applied herbicide was used, yielded less due to a longer period of interference from Florida beggarweed, sicklepod, and pitted morningglory because of the timing of chlorimuron application (60 d after planting).

Nomenclature: Bentazon; chlorimuron; diclosulam; flumioxazin; imazapic; paraquat; 2,4-DB; Florida beggarweed, Desmodium tortuosum S. DC #³ DEDTO; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; peanut, Arachis hypogaea L. ‘Georgia Green’.

Additional index words: Bentazon, chlorimuron, imazapic, paraquat, 2,4-DB, peanut, Arachis hypogaea L. ‘Georgia Green’.

Abbreviations: ALS, acetolactase synthase; EPOST, early postermergence; fb, followed by; WAP, weeks after planting.

Three field trials were conducted in south Georgia under irrigated conditions in 2002/2003 and 2003/2004 to evaluate the effects of imazapic residues on oat growth and yield. Imazapic at 70 g ai/ha was applied during the first weeks of May, June, July, August, and September to bare soil. No additional tillage was performed after the herbicide application. Oats (cv. Coker 227) were planted the first week of October. Oat plant populations were not reduced by any timing of imazapic. Generally, oat plant heights and forage yields were reduced when imazapic was applied in August and September (1–2 mo before planting). Grain yields were not reduced by any timing of imazapic. Results of these tests suggest that the current 18-mo rotational restriction for oats following an application of imazapic could be reduced to 4 mo.

Nomenclature: Imazapic; oats, Avena sativa L. ‘Coker 227’.

Additional index words: Carryover, crop rotations, herbicide persistence, imidazolinone, plant-back restrictions.

Abbreviations: DAP, days after planting.

A field study was conducted in 2002 and 2003 to evaluate the effect of clomazone at 448 g ai/ha plus bensulfuron at 10, 21, 31, and 42 g ai/ha or halosulfuron at 13, 26, 39, and 53 g ai/ha on rice. Herbicide treatments were impregnated onto urea fertilizer and applied at rooting (AR) in a water-seeded production system. Comparison treatments included clomazone AR followed by bensulfuron at 42 g/ha or halosulfuron at 53 g/ha POST. At 7 d after AR (DAAR), rice foliar bleaching decreased from 42% with a single application of clomazone to 23 to 30% with any rate of bensulfuron or halosulfuron impregnated with clomazone. Barnyardgrass and broadleaf signalgrass control did not decrease with the addition of bensulfuron or halosulfuron to clomazone. A single application of clomazone did not control rice flatsedge at 28 DAAR; however, rice flatsedge control was greater than 76% for all bensulfuron and halosulfuron treatments at 28 DAAR. There were no differences in rice yield among herbicide treatments.

Nomenclature: Clomazone; bensulfuron; halosulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; rice flatsedge, Cyperus iria L. # CYPIR; rice, Oryza sativa L. ‘Cocodrie’.

Additional index words: Herbicide tolerance; herbicide-impregnated fertilizer.

Abbreviations: AR, at rooting; DAAR, days after AR; DAT, days after treatment; DPRE, delayed preemergence; fb, followed by.

Field experiments were conducted from 2000 to 2002 at the Southern Maryland Research and Education Facility located in Upper Marlboro, MD to evaluate PPI and preemergence/prior-to-transplanting (PRE-T) applications of sulfentrazone in combination with clomazone or pendimethalin on crop injury and yield of Maryland-type tobacco. Pendimethalin was also evaluated alone. The highest levels of tobacco injury in 2000 occurred 3 wk after treatment (WAT) with PPI applications of sulfentrazone plus pendimethalin at 0.35 0.84 and 0.42 0.84 kg ai/ha, averaging 37 and 28%, respectively. In 2001, PPI applications of sulfentrazone plus clomazone at 0.42 0.84 kg/ha or sulfentrazone plus pendimethalin at 0.42 0.84 kg/ha caused 18 and 12% injury, respectively, 3 WAT. Injury in 2002 with all treatments averaged 7% or less 3 WAT. Greater rainfall through 3 WAT occurred in 2000 than in 2001 or 2002, likely contributing to the higher injury in 2000. Tobacco yields were generally similar among herbicide treatments in 2000 and 2001, and tobacco yields for all herbicide treatments were similar in 2002. The quality index was similar in 2000 and 2001, and varied slightly in 2002 among all herbicide treatments. Although a lower price was calculated for the nontreated controls, price did not vary among most herbicide treatments each year. This research shows that injury to Maryland-type tobacco can occur with sulfentrazone in combination with clomazone or pendimethalin, particularly when incorporated, and when high rainfall occurs soon after transplanting. However, injury is transient and generally has no negative influence on tobacco yield, quality, or price.

Nomenclature: Clomazone; pendimethalin; sulfentrazone; Maryland-type tobacco, Nicotiana tabacum L. ‘MD-609’.

Additional index words: Crop injury, crop price, crop quality, crop yield.

Abbreviations: DAT, days after treatment; PRE-T, preemergence/prior-to-transplanting; WAT, weeks after treatment; WATP, weeks after transplanting.

Field studies were conducted in 1999 and 2000 at seven locations in south Texas to evaluate flufenacet plus isoxaflutole for weed control and corn tolerance. Palmer amaranth control with flufenacent plus isoxaflutole was variable, with no greater than 60% control at one location and greater than 95% control at another. The poor control at the one location was probably due to lack of rainfall for 3 to 4 wk after corn was planted. Flufenacet plus isoxaflutole at 0.56 or 0.7 kg/ha controlled Texas panicum at least 80%, whereas flufenacet plus isoxaflutole rates lower than 0.56 kg/ha provided variable control (55 to 99%). Flufenacet plus isoxaflutole at 0.35 and 0.49 kg/ha controlled pitted morningglory at least 83%. Corn stunting (3 to 16%) with flufenacet plus isoxaflutole was noted at the one location where the soil sand content was greater than 80% and moisture was received within 48 h of herbicide application. With few exceptions, corn weed control and yield with flufenacet plus isoxaflutole combinations were generally comparable to those observed for the atrazine and acetochlor standard treatments.

Nomenclature: Flufenacet; isoxaflutole; Palmer amaranth, Amaranthus palmeri S. Wats. #³ AMAPA; pitted morningglory, Ipomoea lacunosa (L.) # IPOLA; Texas panicum, Panicum texanum Buckl. # PANTE; corn, Zea mays L., ‘AS986’, ‘DK668’, ‘Pioneer 3223’, ‘Pioneer 32K61’.

Additional index words: Corn tolerance, weed management.

There is a limited number of herbicides available for weed control in adzuki bean production in Ontario, Canada. A total of six field trials were conducted in Ontario over a 2-yr period (2003 and 2004) to evaluate tolerance of adzuki bean to preplant incorporated (PPI) application of EPTC (4,400 and 8,800 g ai/ha), trifluralin (1,155 and 2,310 g ai/ha), dimethenamid (1,250 and 2,500 g ai/ha), S-metolachlor (1,600 and 3,200 g ai/ha), and imazethapyr (75 and 150 g ai/ha). All treatments, including the nontreated control, were maintained weed free during the growing season. EPTC and dimethenamid caused as much as 39% visual crop injury and reduced plant height, shoot dry weight, and yield up to 34, 63, and 38%, respectively. Maturity was delayed with the application of EPTC and dimethenamid. Trifluralin caused as much as 9% visual crop injury and decreased plant height up to 11%. There was no effect of trifluralin on shoot dry weight, seed moisture content, and yield. S-metolachlor caused as much as 19% visual crop injury, decreased plant height up to 23%, and reduced shoot dry weight up to 29%. Yield was not affected at the low rate but was decreased 19% at the high rate. There was no effect of S-metolachlor on maturity. Imazethapyr caused up to 6% visual injury but had no adverse effects on plant height, shoot dry weight, seed moisture content, and yield except at the high rate, which caused a 15% reduction in plant height. Based on these results, trifluralin and imazethapyr applied PPI have an adequate margin of crop safety for weed management in adzuki bean production in Ontario.

Nomenclature: Dimethenamid; EPTC; imazethapyr; S-metolachlor; trifluralin.

Additional index words: Adzuki bean, Vigna angularis.(Willd.) Ohwi and Ohashi ‘Erimo’; crop injury; tolerance.

Abbreviations: DAE, days after emergence; PPI, preplant incorporated.

No-till production systems coupled with decreased use of soil residual herbicides has led to increased populations of winter annual weeds. Therefore, research was conducted to quantify the effect of henbit interference and crop stand loss on soft red winter wheat grain yield and grain volume weight. The main-plot effect consisted of weed-free versus weedy plots. The subplot effect was winter wheat stand loss treatments of 0, 20, 40, 60, 80, and 100%. Henbit interference did not affect test weight; however, test weight decreased as percentage of stand loss increased. Henbit did not reduce crop yield at 18 plants/m²; however, at 82 and 155 plants/m², crop yield was reduced 13 and 38%, respectively, when averaged across all stand loss treatments. Yield estimates based on wheat tiller or spike density decreased linearly as crop stand loss increased. Our results indicated that henbit interference coupled with crop stand loss may significantly decrease crop yield and profitability of wheat production systems.

Nomenclature: Sethoxydim; henbit, Lamium amplexicaule L. #³ LAMAM; winter wheat, Triticum aestivum L. ‘Ernie’, ‘Roane’.

Additional index words: Weed competition, yield loss, winterkill.

A field study was conducted in 2002 and 2003 to evaluate tolerance of eight rice cultivars to clomazone at 896 g ai/ha impregnated onto urea fertilizer. Rice foliar bleaching was 16 to 20% at 14 d after rice rooting (DAR) for long-grain cultivars ‘Ahrent’, ‘Cheniere’, ‘Cocodrie’, ‘Cypress’, ‘Francis’, and ‘Wells’ and 23 and 30% for medium-grain ‘Bengal’ and short-grain ‘Pirogue’, respectively, when clomazone was impregnated onto urea. Clomazone reduced the number of tillers/ m² 21 DAR for all cultivars. Early season height reductions occurred for all cultivars; however, Pirogue was the only cultivar shorter than the nontreated at harvest. There were no yield reductions with regard to the medium and long-grain cultivars when compared with respective nontreated cultivars. However, yield of short-grain Pirogue treated with clomazone was 1,740 kg/ha less than the nontreated.

Nomenclature: Clomazone; herbicide-coated fertilizer; rice, Oryza sativa L., ‘Ahrent’, ‘Cheniere’, ‘Cocodrie’, ‘Cypress’, ‘Francis’, ‘Wells’, ‘Bengal’, ‘Pirogue’.

Additional index words: Herbicide tolerance.

Abbreviations: DAE, days after emergence; DAPRE, days after preemergence; DAR, days after rice rooting; DAT, days after treatment; DPRE, delayed preemergence; ME, microencapsulated.

Japanese stiltgrass is a nonnative invasive grass that occurs in a variety of habitats and is widely distributed throughout the eastern United States. In natural areas such as forests, herbicide options that selectively control Japanese stiltgrass while preserving native herbaceous and woody vegetation may be desired. The efficacy of three selective postemergence herbicides (fenoxaprop-P, imazapic, and sethoxydim) applied early season, midseason, or late season on monoculture understory stands of Japanese stiltgrass in forests was examined in an experiment conducted at a site in North Carolina and a site in Virginia from 2002 to 2004. The herbicides, averaged across application timings, controlled Japanese stiltgrass at the end of the growing season 83 to 89% and seedhead production 79 to 94% compared with nontreated plants. Seedling emergence was reduced in the spring of 2004 by 89, 70, and 78% by fenoxaprop-P, imazapic, and sethoxydim, respectively, applied in 2003. In another experiment at the North Carolina site in 2002 and 2003, fenoxaprop-P or sethoxydim applied twice (4 wk apart) at half-registered rates controlled Japanese stiltgrass. This study demonstrates that land managers have multiple POST herbicide and application timing, rate, and frequency options for Japanese stiltgrass control.

Nomenclature: Fenoxaprop-P; imazapic; sethoxydim; Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus #³ MCGVM.

Additional index words: Invasive plant, annual jewgrass, bamboograss, flexible sesagrass, Japanese grass, Mary's grass, Nepalese browntop.

Abbreviations: 1X, maximum use rate.

The effect of application technology on efficacy has been thoroughly investigated for sprays of chemical pesticide but not biological pesticides. This study investigates the effect of applying conidia of Microsphaeropsis amaranthi, a candidate bioherbicide for Amaranthus spp., with a range of different hydraulic nozzle tips. The nozzle tips were selected to deliver sprays with different spectra of droplet sizes deployed at different angles. We found that sprays of large droplets gave poor coverage of the target and resulted in low levels of disease severity on common waterhemp. The most effective nozzle tip tested was a hollow cone nozzle tip, such as is commonly used for the application of fungicides. This nozzle tip deployed large numbers of fine droplets that swirled within the plant canopy, provided good coverage of all plant parts, and resulted in the highest levels of disease severity, particularly on stems.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer, #³ AMATA.

Additional index words: Bioherbicide, application technology, biological control.

Abbreviations: AI, air induction spray tip TeeJet® AI 11004; flat fan, standard flat spray tip TeeJet® TP 110015; full cone, full cone spray tip TeeJet® TG-4; hollow cone, hollow cone spray tip TeeJet® TX-8 Conejet; XR, extended range flat spray tip TeeJet® XR 11001; VMD, volume mean diameter: 50% of the spray volume composed of droplets larger, and 50% of the spray volume composed of droplets smaller, than the VMD.

The value of glyphosate has been compromised in some fields where weed populations have developed resistance or tolerant species increased. Three case studies related to reduced control from glyphosate are: (1) a weed population that has become resistant to glyphosate, with horseweed in Tennessee as an example; (2) a weed population increases due to lack of control in “glyphosate only” systems, with tropical spiderwort in Georgia cotton used as an example; and (3) the hypothetical resistance of common waterhemp to glyphosate in Illinois. For each of these case studies, an economic analysis was performed using a partial budget approach. This economic analysis provides the cost of control to the farmer when glyphosate fails to control these weeds and gives a critical time in years to compare different glyphosate resistance management philosophies (applicable only before resistance has evolved). The cost of glyphosate-resistant horseweed in cotton-soybean-corn rotation in Western Tennessee was calculated to be $30.46/ha per year. The cost of tropical spiderwort in cotton in southern Georgia was calculated to be $35.07/ha per year. The projected cost if common waterhemp were to develop glyphosate resistance in a corn-soybean rotation in southern Illinois was projected to be $44.25/ha per year, and the critical time was determined to be greater than 20 yr, indicating that a resistance management strategy would extend the value of glyphosate-resistant crops.

Nomenclature: glyphosate; common waterhemp, Amaranthus rudis Sauer. #³ AMATA; horseweed, Conyza canadensis L. Cronq # ERICA; tropical spiderwort, Commelina benghalensis L. # COMBE.

Additional index words: economic analysis, herbicide cost, herbicide resistance.

Abbreviations: ALS, acetolactate synthase; C_managing, economic cost of managing resistance; C_resistance, economic cost of resistance; GR, glyphosate resistant; NPV, net present value; NPV_proactive, net present value of proactive resistance management; NPV_reactive, net present value of reactive management; PPO, protoporphyrinogenoxidase; R_resistance, net economic return once resistance has occurred; R_without, net economic return without resistance; T_critical, time at which net present value for reactive and proactive resistance management are equal; T_resistance, time at which resistance occurs.

Field experiments in 2001 and 2002 at Stuttgart, AR, demonstrated cyhalofop applied POST controlled propanil-susceptible barnyardgrass, propanil-resistant barnyardgrass, and broadleaf signalgrass 67, 65, and 71%, respectively 28 days after treatment (DAT). Halosulfuron applied 1 d before cyhalofop or applied in a tank-mixture reduced broadleaf signalgrass and propanil-resistant or propanil-susceptible barnyardgrass by 35 to 59 percentage points. Triclopyr applied 5, 3, or 1 d before, or mixed with, cyhalofop reduced control of propanil-resistant and propanil-susceptible barnyardgrass, 16 to 41 percentage points, respectively. Triclopyr applied 1 d before cyhalofop or combined with cyhalofop reduced broadleaf signalgrass control 38 and 18 percentage points, respectively compared with cyhalofop alone. Propanil reduced cyhalofop grass control only when mixed with cyhalofop. Application timings, averaged across halosulfuron, propanil, and triclopyr, made 1 d before cyhalofop or tank-mixed with cyhalofop reduced grass control more compared with other application timings made before or after cyhalofop. Barnyardgrass absorption of ¹⁴C-cyhalofop alone or mixed with propanil was 86 and 75%, respectively, with ¹⁴C-cyhalofop translocation being reduced by 10-fold when propanil was mixed with cyhalofop. Reductions in cyhalofop translocation in combination with propanil may have partially explained the reductions in grass control observed in the field.

Nomenclature: Cyhalofop; halosulfuron; triclopyr; propanil; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. # BRAPP; rice, Oryza sativa L. ‘Wells’.

Additional index words: ACCase, application timing, herbicide absorption, herbicide translocation, herbicide interaction, propanil-resistant barnyardgrass.

Abbreviations: ACCase, acetyl-CoA carboxylase; ALS, acetolactate synthase; COC, crop oil concentrate; DAT, days after treatment; HAE, hours after exposure; LSS, liquid scintillation spectrophotometry; PS, photosynthetic; SA, synthetic auxin.

Glyphosate-resistant soybean at 494,000 seeds/ha was drill seeded with conventional soybean at 0 to 1,976,000 seeds/ha, and conventional soybean controlled at 2, 4, or 6 wk after soybean emergence with glyphosate at 0.84 kg ae/ha. Weed control increased exponentially with soybean groundcover prior to treatment with glyphosate and was maximized at 69 and 84% for Palmer amaranth and Florida pusley, respectively. When glyphosate was applied 2 wk after soybean emergence, yields were improved 390 kg/ha at 494,000 glyphosate-resistant soybean plus 247,000 conventional soybean seeds/ha compared with glyphosate-resistant soybean alone. Further increases in seeding rate of the conventional soybean often had a negative effect on soybean yields due to interference between glyphosate-resistant and conventional soybean prior to applying glyphosate. Glyphosate applied 6 wk after soybean emergence was generally less effective in controlling Palmer amaranth and Florida pusley than at earlier timings because of weed size at application and the overlying soybean canopy. This research indicates the mix-seeded soybean system may suppress early-season weeds, but glyphosate needs to be applied no later than 4 wk after soybean emergence to ensure optimum yields and prevent interference between glyphosate-resistant and conventional soybean.

Nomenclature: Glyphosate; Palmer amaranth, Amaranthus palmeri S. Wats. #³ AMAPA; Florida pusley, Richardia scabra L. # RCHSC; soybean, Glycine max (L.) Merr.

Additional index words: Application timing, integrated weed management, soybean groundcover, transgenic crop.

Abbreviation: WAE, weeks after soybean emergence.

Studies were conducted at the University of Florida, West Florida Research and Education Center to determine the effect of glyphosate on purple nutsedge control and nutsedge tuber production when glyphosate was applied to the same plots over 3 y in glyphosate-resistant soybean and cotton. Greater than 90% control of purple nutsedge foliage was achieved with a single POST application of glyphosate at 0.9 kg ai/ha in soybean or a sequential glyphosate application of 1.1 kg/ha POST followed by 0.6 kg/ha POST-directed in cotton. By the end of the third year of the study, these same treatments reduced purple nutsedge tuber density to less than 0.2% of the nontreated. In cotton, cultivation alone reduced tuber numbers by greater than 90%. Viability of tubers was also reduced by 80% in soybean and by 65% in cotton in the glyphosate-treated plots. Comparison treatments of imazaquin PRE followed by imazaquin POST in soybean or norflurazon PRE followed by cyanazine plus MSMA POST-directed in cotton also reduced purple nutsedge tuber density by ≥85% after three consecutive years of treatment.

Nomenclature: Cyanazine; glyphosate; fluometuron; imazaquin; MSMA; norflurazon; pendimethalin; purple nutsedge, Cyperus rotundus L., #³ CYPRO; cotton, Gossypium hirsutum L. ‘Delta Pine 5415 RR’; soybean, Glycine max L. ‘Hartz 7555RR’.

Additional index words: CYPRO, transgenic cotton, cultivation, purple nutsedge population dynamics.

Abbreviations: DAP, days after planting; POST-directed, postemergence directed; Early-POST, early postemergence.

Field trials were conducted with sulfentrazone at 53, 80, and 105 g ai/ha combined with 0, 420, and 560 g ai/ha metribuzin in a 3 by 3 factorial arrangement. Sulfentrazone and metribuzin combinations improved control of redroot pigweed, common lambsquarters, hairy nightshade, and volunteer oat compared with sulfentrazone applied alone. Kochia control was more than 90% regardless of metribuzin presence in the treatment. Sulfentrazone at 105 g/ha was needed for greater than 90% hairy nightshade control. Sulfentrazone alone or in combination with metribuzin did not provide greater than 89% volunteer oat control. Potato crop injury was less than 5% and total tuber yields increased as metribuzin rate increased from 0 to 560 g/ha, reflecting improved weed control as metribuzin rate increased.

Nomenclature: Metribuzin; sulfentrazone; potato, Solanum tuberosum L. ‘Russet Burbank’; common lambsquarters, Chenopodium album L. #³CHEAL; hairy nightshade, Solanum sarrachoides Sendter # SOLSA; kochia, Kochia scoparia L. Shrad. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; volunteer oats, Avena sativa L. # AVESA.

Additional index words: Crop safety, herbicide injury, reduced rates.

Abbreviations: OM, organic matter; WAT, weeks after treatment.

Field studies were conducted in 2003 and 2004 near Scottsbluff and Sidney, NE, to identify efficacious chemical weed-control options for irrigated and dryland chickpea production. Weed control had a greater relative effect on chickpea yield in the irrigated system than the dryland system, with yield from the hand-weeded check exceeding the nontreated check by 1,500% in the irrigated system and 87% in the dryland system. Imazethapyr, applied preemergence at the rate of 0.053 kg ai/ha, reduced plant height, delayed plant maturity, and caused leaf chlorosis. At Scottsbluff, preplant-incorporated ethalfluralin caused significant crop injury in 2003, but the ethalfluralin treatment also maintained weed densities 4 wk after crop emergence that were not significantly different than the hand-weeded check at both locations in 2003 and 2004. Treatments containing sulfentrazone provided a similar level of weed control but without any evidence of crop injury. Pendimethalin and pendimethalin dimethenamid-P applied preemergence provided acceptable weed control in the irrigated system, where water was applied within 4 d after herbicide application, but did not provide acceptable control in the dryland system.

Nomenclature: Dimethenamid-P, ethalfluralin, imazethapyr, pendimethalin, sulfentrazone, chickpea, Cicer arietinum L.

Additional index words: Herbicides, garbanzo bean, kabuli chickpea.

Abbreviations: WAE, weeks after emergence.

Treatments of dimethenamid-p at 0.7 kg ai/ha applied PRE in tank mixtures with EPTC (3.4 kg ai/ha), metribuzin (560 g ai/ha), pendimethalin (1.1 kg ai/ha), or rimsulfuron (26 g ai/ha) were compared with the same herbicides applied PRE alone in field efficacy trials in Idaho, Oregon, and Washington. Common lambsquarters, kochia, and redroot pigweed control was generally improved with dimethenamid-p tank mixtures compared with control by any herbicide applied alone except metribuzin. Hairy nightshade control at two locations was generally improved with tank mixtures compared with control by any herbicide applied alone. At Washington, where row spacing was narrower than at other locations, dimethenamid-p alone or in tank mixtures provided similar hairy nightshade control, and this control was greater than control by EPTC, metribuzin, or pendimethalin applied alone. ‘Alturas’, ‘Bannock Russet’, ‘Ranger Russet’, ‘Russet Burbank’, ‘Russet Norkotah’, and ‘Shepody’ potato tolerance to dimethenamid-p PRE at 0, 0.7, or 1.4 kg ai/ha was assessed in weed-free field trials conducted at Aberdeen, ID, in 2002 and 2003. Little or no crop injury was evident during the growing seasons and there were no reductions in U.S. No. 1 and total tuber yields regardless of dimethenamid-p rate or potato variety.

Nomenclature: Dimethenamid; dimethenamid-p; EPTC; metribuzin; pendimethalin; rimsulfuron; potato, Solanum tuberosum L. ‘Alturas’, ‘Bannock Russet’, ‘Ranger Russet’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Shepody’, ‘Superior’; barnyardgrass, Echinochloa crus-galli (L.) Beauv #³ ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; hairy nightshade, Solanum sarrachoides Sendter # SOLSA; kochia, Kochia scoparia (L.) Shrad. # KCHSC; redroot pigweed, Amaranthus retroflexus L. # AMARE; volunteer oat, Avena sativa L. # AVESA.

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

Abbreviations: OM, organic matter; PNW, Pacific Northwest; TMP, tank-mix partner; WAT, weeks after treatment.

Plant competition studies designed to quantify interference between species provide valuable information on competitive interactions and on the effects of agronomic practices on those interactions. The effect of each species' density on the growth of itself and on the growth of the other species is quantified in a series of regression models. Traditionally, the models' regression coefficients have been combined in a series of ratios to quantify relative competitive ability and niche differentiation. Coefficients that are negative (positive interference—facilitation, mutualism) or zero (neutral interference or nonsignificant coefficient) do not lend themselves well to ratio-based methodology because of sign cancellation or undefined values, respectively. As a result, ratio-based methodology is limited to using only positive coefficients (negative interference—amensalism, competition). Rather than using ratios, the absolute-log method uses addition and subtraction of coefficients converted to a pseudologarithmic scale, thus allowing for use of coefficients with values that are negative or zero. As a result, the absolute-log method can be used to quantify relative competitive ability and niche differentiation involving all types of interference—negative, positive, and neutral. The absolute-log method includes an optional statistical procedure constructing confidence intervals for the estimates of relative competitive ability and niche differentiation.

Additional index words: Interference, competition, amensalism, facilitation, mutualism, Spitters, reciprocal yield law.

Abbreviations: A-A, absolute-antilog; AND, absolute-antilog function corollary to ND; ARC, absolute-antilog function corollary to RC; CI, confidence interval; LND, absolute-log method corollary to ND; LRC, absolute-log method corollary to RC; ND, niche differentiation value; RC, relative competitive ability value; SE, standard error.

Herbicides and herbicide prepackaged mixtures registered for use on established bermudagrass turf may cause significant injury to recently seeded bermudagrass cultivars, delaying full establishment. Research was conducted to evaluate the use of 12 herbicide treatments applied at onset of uniform stolon development (4 to 8 wk after seeding) to recently seeded ‘Princess 77,’ ‘Riviera,’ ‘Savannah,’ and ‘Yukon’ bermudagrass cultivars. In general, Yukon was more susceptible to herbicide injury than other cultivars. Atrazine at 1.1 kg ai/ha injured all cultivars 55 to 59% 14 d after initial treatment (DAIT), which lead to reduced bermudagrass cover 21 DAIT. Triclopyr clopyralid at 0.63 0.21 kg ae/ha, respectively, injured Savannah and Yukon greater than other broadleaf weed herbicides (2,4-D mecoprop dicamba or 2,4-D clopyralid dicamba). Foramsulfuron did not injure or reduce bermudagrass cover of any cultivar evaluated at any rating date. The only adverse effect of trifloxysulfuron was a reduction in Riviera and Yukon ground cover at 21 DAIT. MSMA applied sequentially and quinclorac treatments did not injure or reduce ground cover of Savannah or Princess 77. MSMA applied sequentially and/or quinclorac injured and reduced ground cover of Riviera and Yukon; however, both cultivars completely recovered from MSMA or quinclorac injury by 42 DAIT.

Nomenclature: clopyralid, 2,4-D, dicamba, foramsulfuron, mecoprop, MSMA, triclopyr, trifloxysulfuron, quinclorac; common bermudagrass, Cynodon dactylon (L.) Pers. #³ CYNDA, ‘Princess 77’, ‘Riviera’, ‘Savannah’, ‘Yukon.’

Additional index words: Seeded establishment, stolon development, turfgrass tolerance.

Abbreviations: DAIT, days after initial treatment; NTEP, National Turfgrass Evaluation Program.

Field studies were conducted in 1999 to 2000 on a clay soil and a sandy-loam soil in Londrina and Palmeira, PR, Brazil, respectively, to determine the persistence and carryover effect of a mixture of imazapic and imazapyr, applied to imidazolinone-tolerant corn, on rotational crops of soybean, edible bean, wheat, and corn in two different planting systems (no till and tillage). Main plots were herbicide treatments (0, 52.5 17.5, and 105 35 g ai/ha for imazapic and imazapyr, respectively) and subplots were five intervals (0, 30, 60, 90, and 120 d) between the herbicide application and rotational crop planting. Soil samples were collected for a cucumber bioassay and chemical residues analysis at each time interval. The dissipation time (DT₅₀) of the herbicides in the soil was greater in Londrina than Palmeira, for both imazapic (54 d vs. 27 d, respectively) and imazapyr (40 d vs. 33 d, respectively), probably due to the lower pH and greater clay content of the soil in Londrina compared with Palmeira. The DT₅₀ for both herbicides tended to increase slightly in no-till compared with conventional tillage but the differences were not great. Soybean was the least sensitive rotational crop, with a period for no yield drag (PINYD) of 87 d in Londrina and 88 d in Palmeira. Wheat and edible bean showed intermediate sensitivity. The PINYD for wheat and edible bean was 99 and 98 d for Londrina and 91 and 97 d for Palmeira, respectively. Corn was the most sensitive, with a PINYD of 117 d in Londrina and 97 d in Palmeira. Cucumber was more sensitive to imazapic and imazapyr residues than the rotational crops and should be an effective bioassay to indicate when rotational crops can be safely planted.

Nomenclature: Corn, Zea mays L.; cucumber, Cucumis sativus L.; edible bean, Phaseolus vulgaris L., soybean, Glycine max (L.) Merr.; wheat, Triticum aestivum L.

Additional index words: Crop tolerance, imidazolinone, herbicide carryover, dissipation time, planting interval, soil bioassay.

Abbreviations: ALS, acetolactate synthase; CPINI, cucumber planting interval with no injury; DAP, days after planting; DAT, days after treatment; DT₅₀, interval (in days) to degrade 50% of the herbicide rate applied in the soil; LCHS, lowest concentration of the herbicide in the soil which causes crop injury; PINYD, the period between herbicide application and rotational crop planting with no yield drag.

Pendimethalin plus atrazine (1,120 2,240 g ai/ha) or metolachlor plus atrazine (2,170 1,790 g ai/ha) applied PRE over 2 yr controlled broadleaf signalgrass and itchgrass 78 to 88% 30 d after treatment (DAT). The imazethapyr plus imazapyr prepackaged mixture (PREMIX) applied PRE at 47 16 g ai/ha controlled these weeds no more than 35%. With pendimethalin, metolachlor plus atrazine, or atrazine PRE followed by (fb) imazethapyr plus imazapyr POST, broadleaf signalgrass was controlled 89 to 98% and itchgrass 76 to 83% 28 d after POST application. When only imazethapyr plus imazapyr was applied POST, broadleaf signalgrass control was 88% the first year, but only 64% the second year. Itchgrass was controlled 71% when imazethapyr plus imazapyr was applied alone POST, but control was nearly 86% when pendimethalin or nicosulfuron was applied POST with imazethapyr plus imazapyr. Consistently high corn yields were obtained when pendimethalin was applied POST with imazethapyr plus imazapyr, and these corn yields were greater than those following POST-only applications of imazethapyr plus imazapyr in 1 of 2 yr. When imazethapyr plus imazapyr was applied alone POST, corn yield was at least 1.3 times that when imazethapyr plus imazapyr was applied alone PRE. Weed control with imazethapyr plus imazapyr POST at 47 16 g/ha was not improved when ammonium sulfate was added with nonionionic surfactant or when methylated seed oil with or without ammonium sulfate or organosilicone adjuvants were used in the spray solution compared with using only nonionic surfactant in the spray solution. When imazethapyr plus imazapyr plus the various adjuvants was applied to weeds 5 to 8 cm tall, broadleaf signalgrass was controlled 93%, itchgrass 74 and 88%, and pitted morningglory 87 and 93% 28 DAT over 2 yr.

Nomenclature: Atrazine; imazapyr; imazethapyr; metolachlor; nicosulfuron; pendimethalin; broadleaf signalgrass, Brachiaria platyphylla (Griesb.) Nash #³ BRAPP; itchgrass, Rottboellia cochinchinensis (Lour.) W. D. Clayton # ROOEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; corn, Zea mays L. ‘Pioneer 3395 IR.’

Additional index words: Adjuvants, application timing, herbicide combinations, imidazolinone-resistant corn, tank mixture.

Abbreviations: DAT, days after treatment; EPOST, early postemergence; fb, followed by; IR, imidazolinone-resistant; LPOST, late postemergence; PREMIX, prepackaged mixture.

Field studies were conducted from 2000 through 2002 to evaluate the effects of atrazine, pendimethalin, and trifluralin applied alone or in combination followed by cultivation when weeds and grain sorghum were less than 7 cm tall (early postemergence [EPOST]) or when weeds and grain sorghum were 10 to 15 cm tall (late postemergence [LPOST]). Atrazine plus pendimethalin applied EPOST caused 9 to 14% sorghum stunting all 3 yr while atrazine plus trifluralin applied EPOST caused 1 to 4% grain sorghum stunting. When applied LPOST, atrazine plus pendimethalin or trifluralin resulted in no greater than 3% stunting. Tumble pigweed was controlled at least 99% with atrazine plus pendimethalin or trifluralin applied EPOST or LPOST, whereas Texas panicum was controlled at least 97% with atrazine plus pendimethalin or trifluralin applied EPOST, and 76 to 100% with LPOST application. Sorghum yields were reduced with atrazine plus pendimethalin applied EPOST when compared with all herbicide combinations in one of 3 yr.

Nomenclature: Atrazine; pendimethalin; trifluralin; tumble pigweed, Amaranthus albus L. #³ AMAAL; Texas panicum, Panicum texanum Buckl. # PANTE; grain sorghum, Sorghum bicolor (L.) Moench. ‘DKS 54-00’, ‘Pioneer 8313’.

Additional index words: Cultivation, crop tolerance, stunting, yield reduction.

Abbreviations: EPOST, early postemergence; LPOST, late postemergence; WAP, weeks after planting.

Greenhouse experiments were conducted in the summer of 2002 to determine the effect of root-knot nematodes on purple nutsedge suppression and chile pepper response after applications of halosulfuron. Purple nutsedge and chile pepper plants were grown together in 20-cm-diam pots, inoculated with root-knot nematodes, and treated with halosulfuron 2 or 4 wk after inoculation. Root-knot nematode infection had no effect on purple nutsedge control or chile pepper injury after treatment with halosulfuron, regardless of application timing. However, root-knot nematode reproduction was lower in pots that received a halosulfuron treatment, particularly halosulfuron applied 2 wk after inoculation. Controlling purple nutsedge using halosulfuron in a field infested with root-knot nematodes could also decrease the amount of nematode inoculum that is available for infecting chile plants later in the season.

Nomenclature: Halosulfuron; purple nutsedge, Cyperus rotundus L. #³ CYPRO; chile pepper, Capsicum annuum L. ‘Joe E. Parker’; southern root-knot nematode, Meloidogyne incognita (Kofoid and White) Chitwood, host race 3.

Additional index words: Pest interactions, ALS herbicide, Capsicum annuum, CYPRO.

Abbreviations: GH1, first greenhouse experiment; GH2, second greenhouse experiment; GH3, third greenhouse experiment.

A study was conducted in 2004 to determine the effect of coapplication of the insecticides acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emanectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, thiamethoxam, and zeta-cypermethrin; the plant growth-regulator mepiquat pentaborate; a foliar sodium calcium borate micronutrient solution; and a foliar nitrogen fertilizer solution with glyphosate on the efficacy of weeds that commonly infest cotton. Barnyardgrass, hemp sesbania, johnsongrass, pitted morningglory, and sicklepod were grown in outdoor containers and treated with glyphosate at 1,120 g ai/ha alone or in coapplication at the three-to four- or seven-to eight-leaf growth stage. Glyphosate efficacy, based on visual control ratings at 7, 14, and 28 d after treatment (DAT) and fresh weight reduction of weed biomass at 28 DAT, was unaffected by chemical coapplication or application timing. Averaged across application timing and visual rating interval, glyphosate alone controlled barnyardgrass 97%, hemp sesbania 68%, johnsongrass 98%, pitted morningglory 68%, and sicklepod 89%. These results indicate that glyphosate coapplications evaluated offer producers the ability to combine pest and crop management strategies and reduce application costs without sacrificing control of weeds evaluated.

Nomenclature: Acephate; acetamiprid; bifenthrin; cyfluthrin; cypermethrin; dicrotophos; dimethoate; emanectin benzoate; glyphosate; imidacloprid; indoxacarb; lambda-cyhalothrin; mepiquat pentaborate; methoxyfenozide; nitrogen fertilizer solution, (18.8% urea nitrogen and 6.2% water-soluble nitrogen); sodium calcium borate 10%; spinosad; thiamethoxam; zeta-cypermethrin; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. #³ ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB.

Additional index words: Herbicide–insecticide combinations, pesticide compatibility.

Abbreviations: DAT, days after treatment; RCB, randomized complete block.

Winter cover crops are increasingly common on organic and conventional vegetable farms on the central coast of California between periods of intensive vegetable production. A 2-yr study was conducted in Salinas, California, to quantify (1) cover crop and weed biomass production during cover cropping, (2) early-season canopy development of cover crops, (3) weed seed production by burning nettle during cover cropping, and (4) weed emergence following cover crop incorporation. The cover crops included oats, a mustard mix, and a legume/oats mix that were planted in October and soil-incorporated in February. Weed and cover crop densities, early-season cover crop canopy development, above-ground weed and cover crop biomass production, seed production by the burning nettle, and postincorporation weed emergence was evaluated. Mustard produced more early-season biomass than oats and the legume/oats mix. There were no differences in above ground biomass production by the cover crops at the end of their growth period. Suppression of weed biomass and seed production of burning nettle was greatest in mustard, and least in oats and the legume/oats mix. The weed suppressive ability of each cover crop was affected by early-season canopy development and was highly correlated with cover crop plant density. Weed emergence following cover crop incorporation was in order of legume/oats mix > oats > mustard in yr 1, but was not different in yr 2. This study provides initial information on cover crop effects on weed management in irrigated and tilled vegetable production systems in the central coast of California. The results suggest that the legume/oats mix could exacerbate weed problems in subsequent vegetable crops.

Nomenclature: Burning nettle, Urtica urens L. #³ URTUR; bell beans, Vicia faba L.; common vetch, Vicia sativa L.; lana vetch, Vicia villosa ssp. dasycarpa Roth; mustards, Brassica juncea (L.) Czern., Brassica hirta Moench; oats, Avena sativa L.; peas, Pisum sativum L.

Additional index words: biomass production, canopy development, weed seed production, weed-suppressive ability.

Abbreviations: DAI, days after incorporation; DAP, days after planting.

Canada thistle is one of the most troublesome and difficult weed species to control in established alfalfa grown for seed production. Current tools available for control are limited because of cultural management strategies associated with seed production. Alfalfa seed losses due to Canada thistle interference include both reduced yields from competition and increased seed loss during seed cleaning operations. Additional tools are needed to alleviate these losses. Field experiments were conducted in 1998, 1999, and 2000 at two locations in Park County, WY, to evaluate Canada thistle control and alfalfa tolerance to several postemergence herbicides. Bentazon, imazamox, imazethapyr, and MCPB were applied, alone or in combination, at different Canada thistle growth stages. Methylated seed oil (MSO) was added at 1.5% v/v to the treatments containing imazamox or imazethapyr. MCPB applied alone when Canada thistle was 7.5- or 15-cm tall caused severe alfalfa injury (28 to 40%) and resulted in less Canada thistle control (23 to 27%). Imazamox or imazethapyr applied alone when Canada thistle was 15-cm tall did not cause any significant alfalfa injury but resulted in unsatisfactory Canada thistle control (29 to 35%). Bentazon was the only treatment containing a single herbicide that provided more than 50% Canada thistle control. The treatments providing the best balance between Canada thistle control (>80%) and alfalfa injury (<13%) were a single application of bentazon combined with either imazamox or imazethapyr. These two treatments also yielded the highest, more than 800 kg/ha. Split applications of bentazon combined with imazamox or imazethapyr were similar to single applications.

Nomenclature: Bentazon; imazamox; imazethapyr; MCPB; Canada thistle, Cirsium arvense (L.) Scop. #³ CIRAR; Alfalfa, Medicago sativa L.

Additional index words: Application timing, herbicide mixtures, methylated seed oil, MSO, postemergence, weed management, CIRAR.

Abbreviations: IMI, imidazolinone-resistant; MSO, methylated seed oil.

Studies were conducted on the campuses of Texas A&M University in College Station, TX, and New Mexico State in Las Cruces, NM, to determine the spray droplet size spectra produced by quinclorac and 2,4-D as the liquid, dry, and emulsion formulations during application with various nozzle sizes using a laser spectrometer. Quinclorac and 2,4-D formulations were also sprayed through three different nozzle sizes in a drift chamber and allowed to settle on glass slides placed downwind. The amounts of each herbicide deposited on the slides were quantified using high-performance liquid chromatography/photodiode array (HPLC/PDA) analysis to assess spray deposition of each formulation at different wind velocities. Data from the laser spectrometer suggested that formulations of 2,4-D affected droplet size, particularly when the 380 ml/min flat-fan nozzle was used. Quinclorac droplet sizes were similar to water regardless of nozzle size. Liquid and dry-formulated 2,4-D tended to be deposited downwind in greater quantities than the emulsion formulation when using the 380 and 760 ml/min spray nozzles with wind velocity of 15 km/h.

Nomenclature: 2,4-D, quinclorac.

Additional index words: Laser spectrometer, drift chamber.

Abbreviations: HPLC, high performance liquid chromatography; HSD, honestly significant difference; PDA, photodiode array.

Field studies were conducted in 1997 and 1998 to evaluate the efficacy of imidazolinone weed management systems and crop tolerance of imidazolinone-tolerant (IT) corn to imazapic. Imazapic (36 and 72 g/ha) was evaluated when applied PRE; early postemergence (EPOST), when corn was at the two- to three-leaf stage; and late postemergence (LPOST), when corn was at the six- to eight-leaf stage. Imazapyr imazethapyr EPOST and metolachlor atrazine followed by (fb) primisulfuron LPOST were evaluated as commercial standards. Imazapic at 36 g/ha EPOST controlled johnsongrass, Texas panicum, smellmelon, and ivyleaf and entireleaf morningglory at least 93% when adequate rainfall occurred. Devil's claw was controlled at least 85% with imazapic EPOST or LPOST at either rate. Imazapic at 36 g/ha EPOST and LPOST controlled eclipta 88 and 91%, respectively. Yellow nutsedge was controlled >91% with imazapic LPOST, which was superior to imazapic applied EPOST. Broadleaf signalgrass was controlled 94% with imazapic at 72 g/ha LPOST, which was significantly higher than other herbicide treatments. Imazapic at 36 and 72 g/ha applied PRE under moisture stress resulted in reduced weed control; but when adequate rainfall occurred, weed control was generally similar to that of EPOST and LPOST applications. Imazapic crop response at 72, 105, 140, and 211 g/ha applied at EPOST and LPOST was evaluated in two IT corn hybrids. Crop response varied with soil and environmental conditions and application timings. Imazapic at 72, 105, and 140 g/ha EPOST resulted in crop injury 33 to 55% at 6 wk after planting (WAP) in a coarse soil; however, crop injury decreased to <20% at 12 WAP. Low crop injury (<9%) was observed at 12 WAP in a clay soil. Imazapic applied LPOST resulted in lower crop injury than EPOST application. Corn plant height and yield were not affected by any imazapic treatment.

Nomenclature: Imazapic; imazapyr; imazethapyr; atrazine; metolachlor; primisulfuron; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. #³ IPOHE; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHE; smellmelon, Cucumis melo (L.) var. dudaim Naud. # CUMMD; Texas panicum, Panicum texanum Buckl. # PANTE; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; devil's-claw, Proboscidea louisianica (Mill.) Thellung # PROLO; eclipta, Eclipta prostrata L. # ECLAL; yellow nutsedge, Cyperus esculentus L. # CYPES; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; corn, Zea mays L., ‘Garst 8326IT’, ‘Garst 8396IT’, ‘Cargill 7994IT’, ‘Garst 8222IT’.

Additional index words: Crop response, application timings.

Abbreviations: EPOST, early postemergence; fb, followed by; IR, imidazolinone-resistant; IT, imidazolinone-tolerant; LPOST, late postemergence; TAES, Texas Agricultural Experiment Station Field Laboratory; TP, TP Farms; WAP, weeks after planting.

Field trials were conducted in 2000, 2001, and 2002 at Tifton, GA, and Plains, GA, to evaluate the effects of simulated imazapic residues on cotton growth and yield. Preemergence applications of imazapic at 1, 2, 5, 9, 18, and 36 g ai/ha were made to four different cotton varieties (two at each location) and included a nontreated control. There were no differences in cotton variety response to imazapic. Each cotton variety responded to imazapic in a similar manner. Analysis of cotton yield as a percentage relative to the nontreated control indicated no difference in variety for location, so data for varieties were combined. At Tifton, cotton injury was exponentially related to imazapic rate with a maximum injury of 44% for 35 g/ha. Seed cotton yields at this location were reduced 0, 6, 6, 14, 16, 34, and 61% at 1, 2, 5, 9, 18, and 36 g/ha, respectively. For Plains, cotton exhibited extreme sensitivity with injury exceeding 70% for imazapic at 5 g/ha and greater than 95% for 18 g/ha. Seed cotton yields at this location were reduced 60% or more from imazapic rates of 5 g/ha and greater. These results indicated that soil type is a key factor in the response of cotton to imazapic.

Nomenclature: Imazapic; cotton, Gossypium hirsutum L.

Additional index words: Carryover injury, herbicide persistence, residual herbicide, simulated carryover.

Abbreviations: CEC, cation-exchange capacity; DAT, days after treatment.

Few herbicides are used in carrot production in the United States, and none suppress volunteer potato, a serious weed where the two crops are grown in rotation. Hand-weeding is the primary method of controlling emerged volunteer potato within carrot. The objective of this work was to evaluate carrot tolerance and volunteer potato control with single or sequential applications of prometryn, prometryn plus fluroxypyr, and ethofumesate. The treatment with fluroxypyr resulted in malformed carrots with numerous root hairs and reduced carrot yield. Treatments with prometryn, either as single or sequential POST applications at 2.23 kg ai/ha, were safe on carrot and frequently controlled volunteer potato similar to the hand-weeded treatment. Ethofumesate applied as single or sequential PRE or POST at 2.2 kg ai/ha proved safe on carrot, but higher rates reduced yield. Ethofumesate applied POST or PRE followed by POST consistently reduced volunteer potato tuber mass. If registered for use in carrot, prometryn and ethofumesate would help modernize weed management in carrot and reduce or eliminate the need for hand-weeding volunteer potato.

Nomenclature: ethofumesate; fluroxypyr; prometryn; potato, Solanum tuberosum L.; carrot, Daucus carota L.

Additional index words: Crop injury, integrated weed management, minor crop, tuber density, vegetable.

Abbreviations: EPOST, early postemergence; LPOST, late-postemergence; MPOST, midpostemergence.

Field studies were conducted in 2000 and 2001 to evaluate corn yield-loss predictions generated by WeedSOFT, a computerized weed management decision aid. Conventional tillage practices were used to produce corn in 76-cm rows in Illinois, Indiana, Kansas, Michigan, Missouri, Nebraska, and Wisconsin. A total of 21 site-years from these seven states were evaluated in this study. At 4 wk after planting, weed densities and size, crop-growth stage, estimated weed-free yield, and environmental conditions at the time of application were entered into WeedSOFT to generate POST treatments ranked by percent maximum yield (PMY). POST treatments were chosen with yield losses ranging from 0 to 20%. Data were subjected to linear regression analysis by state and pooled over all states to determine the relationship between actual and predicted yield loss. A slope value equal to one implies perfect agreement between actual and predicted yield loss. Slope value estimates for Illinois and Missouri were equal to one. Actual yield losses were higher than the software predicted in Kansas and lower than predicted in Michigan, Nebraska, and Wisconsin. Slope value estimate from a data set containing all site years was equal to one. This research demonstrated that variability in yield-loss predictions occurred at sites that contained a high density of a single weed specie (>100/m²) regardless of its competitive index (CI); at sites with a predominant broadleaf weed with a CI greater than five, such as Palmer amaranth, giant ragweed, common sunflower, and common cocklebur; and at sites that experience moderate to severe drought stress.

Nomenclature: common cocklebur, Xanthium strumarium L. #³ XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; common sunflower, Helianthus annuus L. # HELAN; common waterhemp, Amaranthus rudis Sauer. # AMATA; corn, Zea mays L. # ZEAMX; eastern black nightshade, Solanum ptycanthum Dun. # SOLPT; green foxtail, Setaria viridis (L.) Beauv. # SETVI; giant foxtail, Setaria faberi Herrm. # SETFA; giant ragweed, Ambrosia trifida L. # AMBTR; fall panicum, Panicum dichotomiflorum Michx. # PANDI; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; morningglory spp., Ipomoea spp. # IPOSS; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; Venice mallow, Hibiscus trionum L. # HIBTR.

Additional index words: Bioeconomic model, decision support system, herbicide decision aid.

Abbreviations: CI, competitive index; DSS, decision support system; HPMY, highest percent maximum yield; PMY, percent maximum yield; TCL, total competitive load.

Corn and soybean farmers across Indiana were surveyed in 2003 to determine the perceived importance of weeds at the state and district levels. Weeds were considered the primary crop pest by 69 to 84% of farmers, depending on district. Diseases or insects were ranked first by no more than 14% of farmers and nematodes were ranked first by no more than 11%. Giant ragweed, Canada thistle, common lambsquarters, common cocklebur, and velvetleaf were considered the most problematic summer annual and perennial weeds statewide. Chickweed, horseweed, dandelion, and henbit were considered the most problematic winter annual weeds statewide. However, no weed species was listed by more than 41% of farmers statewide suggesting that relatively unique weed management problems may exist on many farms. Also, the perceived importance of most weed species varied substantially among Indiana's nine districts. For example, velvetleaf was not listed as a problematic weed by any farmers in three districts. Burcucumber was not considered a statewide problem but was listed among the top three weeds by 14 and 16% of farmers in two southern districts. This survey supports the idea that educational programs focused on weed management should be tailored to geographic regions within Indiana.

Nomenclature: Burcucumber, Sicyos angulatus L. #³ SIYAN; Canada thistle, Cirsium arvense (L.) Scop. # CIRAR; chickweed, Stellaria media (L.) Vill. # STEME; common cocklebur, Xanthium strumarium L. # XANTH; common lambsquarters, Chenopodium album L. # CHEAL; dandelion, Taraxacum officinale Weber in Wiggers # TAROF; giant ragweed, Ambrosia trifidia L. # AMBTR; henbit, Lamium amplexicaule L. # LAMAM; horseweed, Conyza canadensis (L.) Cronq. # ERICA; velvetleaf, Abutilon theophrasti L. # ABUTH; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Additional index words: pests, weed rankings, winter annual, summer annual, perennial, Sorghum halepense, Sorghum bicolor, # SORVU, # SORHU.

Abbreviations: GDD, growing degree days; IASS, Indiana Agricultural Statistics Service.