Abstract: An isolate of the fungus Dactylaria higginsii obtained from purple nutsedge in Florida was highly pathogenic to Cyperus spp. The potential of this isolate as a bioherbicide was field tested in natural populations of purple nutsedge in Gainesville and Jay, FL. The fungus was applied in 0.5% Metamucil® as a carrier, and the treatments were: carrier only, 10⁵ conidia/ml carrier, and 10⁶ conidia/ml carrier. Treatments were applied as single, double, or triple postemergence (POST) sprays at biweekly intervals. The disease and secondary infections developed in about 5 and 15 d after inoculation, respectively, killing most of the infected leaves. All weed growth parameters and disease progress rates were affected by inoculum dosage and inoculation frequencies. Three inoculations, each at 10⁶ conidia/ml, provided effective control of purple nutsedge compared to a single inoculation, as measured by shoot dry weight, tuber numbers, and tuber dry weight. Higher rates of disease progress and disease levels, defined by the area under the disease progress curve (AUDPC), occurred with three inoculations at 10⁶ conidia/ml. Disease progress was slower and the level of weed control was lower at 10⁵ conidia/ml compared to the higher inoculum level. Three applications of 10⁶ conidia/ml provided >90% nutsedge control. Dactylaria higginsii appears to be an effective bioherbicide candidate deserving further development for commercial use.

Nomenclature: Purple nutsedge, Cyperus rotundus L., #³ CYPRO, Dactylaria, D. higginsii (Luttrell) M. B. Ellis.

Additional index words: Mycoherbicide, biological control of weeds, fungal pathogen.

Abbreviations: AUDPC, area under the disease progress curve; PDA, potato dextrose agar; POST, postemergence; r_G, disease progress.

Abstract: Buried feral rye seeds were rapidly depleted in soil in the first year due to in situ germination. Less than 1% of the viable seeds persisted after 45 mo of burial. Although after 5 yr, a small number of seedlings still emerged, soil seedbank decline was rapid when seed production was prevented. A low level of induced dormancy was detected and may explain the small populations of feral rye that persisted. Seed and seedling population shifts were large over a 5-yr period and were related to environmental conditions. Tillage or chemical control of feral rye in the fallow period reduced populations compared to the untreated weedy check. Moldboard plowing provided the greatest feral rye control compared to shallow tillage and chemical fallow. Feral rye seedbank populations rebounded following a wet final year of the study. These results help explain feral rye persistence in a wheat–fallow agroecosystem by the persistence of a small portion of the seedbank and by large seed inputs into the system during environmentally favorable years. Feral rye reduced wheat yield as much as 92% and represented up to 73% contamination in harvested wheat.

Nomenclature: Feral rye, Secale cereale L. #³ SECCE.

Additional index words: Volunteer rye, dormancy, population dynamics, seed burial, feral rye management, weed competition.

Abstract: Experiments were conducted to determine whether antagonism between atrazine and glyphosate on shattercane observed in field studies could be duplicated under greenhouse conditions on ‘Rox Orange’ forage sorghum and whether it could be overcome by the addition of ammonium sulfate, other adjuvants, or additional glyphosate. Atrazine or surfactant added to glyphosate did not significantly affect sorghum dry weights compared to glyphosate alone. The Colby equation for synergism indicated that atrazine did not antagonize sorghum control with glyphosate in the greenhouse. Glyphosate at 0.43 kg ae/ha plus ammonium sulfate provided greater control of sorghum than glyphosate at 0.43 kg/ha without ammonium sulfate; however, glyphosate at 0.84 kg/ha plus ammonium sulfate did not provide greater control of sorghum than glyphosate at 0.84 kg/ha without ammonium sulfate. Reduced activity of glyphosate at 0.43 kg/ha in the absence of ammonium sulfate was likely due to an abundance of calcium cations in the carrier water that associated with glyphosate molecules and subsequently reduced herbicide uptake by plants. Thus, antagonism observed under cool conditions in field studies was not evident in controlled-temperature greenhouse studies.

Nomenclature: Atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; glyphosate, N-(phosphonomethyl)glycine; ‘Rox Orange’ sorghum and shattercane, Sorghum bicolor (L.) Moench #³ SORVU.

Additional index words: Antagonism, surfactant.

Abstract: New weed management tools and growth regulators make production of ultra narrow row (UNR) cotton possible. Weed control, cotton yield, fiber quality, and net returns were compared in UNR bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton. Weeds included broadleaf signalgrass, carpetweed, common cocklebur, common lambsquarters, common ragweed, goosegrass, jimsonweed, large crabgrass, Palmer amaranth, pitted morningglory, prickly sida, sicklepod, smooth pigweed, and tall morningglory. Pendimethalin preplant incorporated (PPI) in conventional-tillage or preemergence (PRE) in no-till systems plus fluometuron PRE did not adequately control many of these weeds. Pyrithiobac plus MSMA early postemergence (POST) often was more effective than pyrithiobac alone. Pendimethalin plus fluometuron at planting followed by pyrithiobac plus MSMA early POST controlled sicklepod 82%, goosegrass 89%, Palmer amaranth 92%, and the other species at least 95% late season. Pyrithiobac at mid-POST did not improve control. Bromoxynil plus MSMA early POST was more effective than bromoxynil alone only on sicklepod. Pendimethalin plus fluometuron at planting followed by bromoxynil plus MSMA early POST controlled sicklepod 62%, Palmer amaranth 81%, goosegrass 83%, and all other species at least 95%. Glyphosate early POST did not adequately control many species due to sustained weed emergence. Glyphosate early POST followed by glyphosate late POST (after last effective bloom date) controlled all species except pitted morningglory and tall morningglory at least 93%. Pendimethalin plus fluometuron followed by glyphosate early POST was the most effective glyphosate system overall, and it controlled sicklepod 88%, pitted morningglory 90%, and other species at least 93%. Glyphosate late POST did not increase control in systems with pendimethalin plus fluometuron at planting followed by glyphosate early POST. Yields and net returns were similar with all herbicide/cultivar systems at two of five locations. At other locations, yields and net returns were similar with systems of pendimethalin plus fluometuron at planting followed by pyrithiobac plus MSMA early POST, pendimethalin plus fluometuron followed by bromoxynil plus MSMA early POST, and glyphosate early POST. Greatest yields and net returns were obtained with pendimethalin plus fluometuron at planting followed by glyphosate early POST. Herbicide systems did not affect fiber quality.

Nomenclature: Bromoxynil, 3,5-dibromo-4-hydroxybenzonitrile; fluometuron, N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl]urea; glyphosate, N-(phosphonomethyl)glycine; MSMA, monosodium methanearsonate; pendimethalin, N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine; pyrithiobac, 2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio]benzoic acid; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; jimsonweed, Datura stramonium L. # DATST; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; cotton, Gossypium hirsutum L. ‘Deltapine 51,’ ‘Paymaster 1220RR,’ ‘Stoneville BXN 47.’

Additional index words: Bromoxynil-resistant cotton, cotton yield, fiber quality, glyphosate-resistan

Abstract: Experiments compared the effect on weed control and potato yield of banded applications of metolachlor plus linuron with or without flex-tine, rolling, and shovel cultivation prior to hilling. Cultivation without banded herbicide resulted in greater prehilling in- and between-row weed densities and reduced late-season weed control as compared to broadcast herbicides or cultivation with banded herbicides. Although the flex-tine and rolling cultivators were expected to provide improved in-row weed control, there were few differences between these and the other cultivation implements. Despite reduced weed control with cultivation alone, potato yields were not reduced.

Nomenclature: Linuron, N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; common lambsquarters, Chenopodium album L. #³ CHEAL; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; redroot pigweed, Amaranthus retroflexus L. # AMARE; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; potato, Solanum tuberosum L. ‘Katahdin’.

Additional index words: Flex-tine cultivator, herbicide reduction, mechanical weed control.

Abbreviations: DAP, days after planting.

Abstract: Weeded check plots are an integral part of most weed control experiments. They provide a measure of the maximum crop yield without weed competition in a given site-year environment. The traditional way to create weeded check plots is to hoe and pull weeds by hand in the row and hoe weeds between rows. But erratic heavy rainfall can prevent timely hoeing. The objective of this experiment was to compare faster, less-laborious mechanized ways to control weeds between crop rows as alternatives to hoeing in corn and soybean. Hoeing, the traditional method for controlling weeds between crop rows, was compared with either repeated mowing using a cord-mower or a string-trimmer or shallow tilling with a rototiller between rows. Weeds growing in rows were controlled by hand-pulling and hoeing because the focus of the experiment was on speeding weed control between rows. All four methods for controlling weeds between crop rows were equally effective when measured as either corn or soybean yield, visual rating of weed control, or weed ground cover in two years under contrasting rainfall patterns. Cord-mowing or string-trimming between rows was possible when soil was dry enough to walk upon but too wet to hoe or rototill.

Nomenclature: Corn, Zea mays L. ‘Pioneer 3379’; soybean, Glycine max (L.) Merr. ‘Pioneer 9381’.

Additional index words: Mowing, rototilling, sustainable agriculture, tillage, SETFA.

Abbreviations: BR, between row; IR, in row.

Abstract: Producers in the semi-arid Great Plains are starting to grow corn in sequence with winter wheat and proso millet. However, volunteer proso millet (hereafter referred to as proso) is difficult to control in corn with conventional practices. This study characterized growth and interference of proso in corn to aid producers in developing control strategies. Proso seedlings began emerging May 18 with 78% of seasonal emergence occurring by June 22; initial proso emergence occurred within 2 wk of corn emergence in all years. Seed production was related to time of emergence; proso seedlings emerging in mid-May produced approximately 2,800 seeds per plant, whereas seedlings emerging 4 wk later produced 88% fewer seeds. Controlling proso in late June prevented loss of corn grain yield caused by competition. When corn was planted in early May, the height difference between corn and proso was sufficient to allow postemergence-directed applications of graminicides for proso control. Corn yield was highest when planted in early May.

Nomenclature: Proso millet, Panicum milaceum L. #³ PAMIL; corn, Zea mays L. ‘Pioneer hybrid 3732’; wheat, Triticum aestivum L.

Additional index words: Critical period of interference, emergence period, transgenic corn, PAMIL.

Abbreviations: GDD, growing degree days.

Abstract: Field studies were conducted to evaluate the tolerance of peanut cultivars ‘Florunner’, ‘Georgia Green’, ‘Sunoleic 95R’, ‘AgriTech GK7’, ‘NC-7’, ‘ViruGard’, and ‘Spanco’ to sulfentraone. Herbicide treatments included sulfentrazone applied as a single treatment preemergence (PRE) at 0.14, 0.21, 0.28, 0.35, or 0.42 kg ai/ha or as a PRE followed by (fb) an at cracking (AC) application (0.14 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.14 kg ai/ha AC, 0.21 kg ai/ha PRE fb 0.21 kg ai/ha AC, 0.28 kg ai/ha PRE fb 0.07 kg ai/ha AC, or 0.28 kg ai/ha PRE fb 0.14 kg ai/ha AC). Imazapic and paraquat applied early postemergence (EPOT) were included along with a weed-free control. NC-7 exhibited higher early-season injury (ranging from 1 to 29%) than other cultivars across all sulfentrazone applications. However, this injury did not affect yield when compared with the untreated weed-free check. Overall, peanut tolerance to sulfentrazone was high across all varieties.

Nomenclature: Imazapic, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid); paraquat-dichloride, 1,1′-dimethyl-4,4′-bipyridinium dichloride; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)]-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide; peanut, Arachis hypogaea L., ‘AgriTech GK7’, ‘Florunner’, ‘Georgia Green’, ‘NC-7’, ‘Sunoleic 95R’, ‘Spanco’, ‘ViruGard’.

Additional index words: Peanut injury, peanut cultivar, peanut yield, herbicide susceptibility.

Abbreviations: AC, at cracking; ALS, acetolactate synthase; EPOT, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Abstract: Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and Urbana, IL, to evaluate crop injury, weed control, corn yield, and net economic returns provided by weed control programs in glyphosate-resistant corn. The herbicide programs evaluated included acetochlor preemergence (PRE) followed by (fb) glyphosate with or without atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glyphosate alone and tank-mixed with actochlor, atrazine, or both. Metolachlor PRE fb dicamba plus atrazine POST and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-post (MPOST) applications provided better control than early-post (EPOST) applications on weeds that germinated throughout the growing season such as shattercane and common cocklebur, but also resulted in yield reductions of up to 23% caused by early-season weed competition. The addition of atrazine to glyphosate POST generally increased control of common cocklebur, morningglory species, and common waterhemp. EPOST or PRE fb EPOST applications generally provided higher yields than MPOST treatments, although MPOST treatments often provided equal or greater weed control at midseason. Treatments including two herbicide applications tended to provide greater weed control, yield, and profit than those with a single application. Input costs for glyphosate-resistant corn are slightly higher than nontransgenic hybrids. However, net economic returns are similar and the use of glyphosate POST allows greater flexibility in POST weed management decisions.

Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; dicamba, 3,6-dichloro-2-methoxybenzoic acid; glyphosate, N-(phosphonomethyl)glycine; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; common cocklebur, Xanthium strumarium L.#³ XANST; common waterhemp, Amaranthus rudis Sauer # AMATA; ivyleaf morningglory, Ipomoea hederaceae (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; shattercane, Sorghum bicolor (L.) Moench. # SORVU; corn Zea mays L. # ZEAMX ‘MON802’.

Additional index words: Corn yield, acetochlor, atrazine, dicamba, economic returns, metolachlor, AMATA, ABUTH, CHEAL, IPOHE, IPOLA, POLPY, SETFA, SORVU, XANST, ZEAMX.

Abbreviations: ALS, autolactate synthase; EPOST, early postemergence; fb, followed by; MPOST, mid-postemergence; OM, organic matter; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Abstract: In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.

Nomenclature: Nicosulfuron, 2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide; primisulfuron, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; itchgrass, Rottboellia cochinchinensis (Lour.) W. Clayton #³ ROOEX; corn, Zea mays L. ‘DeKalb 689’.

Additional index words: Crop oil concentrate, methylated seed oil, nonionic surfactant, organosilicone surfactant, ROOEX.

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

Abstract: A 4-yr field study was conducted to evaluate yellow nutsedge suppression in ‘Tifway’ bermudagrass. Herbicide programs included preemergence (PRE) applications of metolachlor (3.4 kg ai/ha) and postemergence (POST) applications of imazaquin (0.28 kg ai/ha) plus MSMA (2.2 kg ai/ha) or halosulfuron (0.07 kg ai/ha) plus MSMA (2.2 kg/ha). Herbicides were applied to the same plots each year. Yellow nutsedge shoot suppression and tuber numbers were determined each year. Suppression of yellow nutsedge shoots increased over the 4-yr period from <74% in 1993 to >83% by 1996 with two annual applications of imazaquin plus MSMA or halosulfuron plus MSMA. PRE metolachlor applications did not suppress shoot production in any year; nor did they enhance suppression from POST treatments. Sequential applications of halosulfuron plus MSMA and imazaquin plus MSMA increased shoot suppression by 17 to 24% at 3 mo after initial treatment (MAIT) compared to single applications. All treatments reduced tuber numbers (>60%) after 4 years compared to untreated plots.

Nomenclature: Halosulfuron, methyl 5-{[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl-aminosulfonyl}-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; metolachlor, [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]; MSMA, monosodium salt of methylarsonic acid; yellow nutsedge, Cyperus esculentus L. #³ CYPES; bermudagrass, Cynodon dactylon Burtt-Davey X C. transvaalensis L. Pers. ‘Tifway’.

Abbreviations: MAIT, months after initial treatment; POST, postemergence; PRE, preemergence; WAIT, weeks after initial treatment.

Abstract: An experiment was conducted at six locations in North Carolina to compare weed-management treatments using glufosinate postemergence (POST) in glufosinate-resistant soybean, glyphosate POST in glyphosate-resistant soybean, and imazaquin plus SAN 582 preemergence (PRE) followed by chlorimuron POST in nontransgenic soybean. Prickly sida and sicklepod were controlled similarly and 84 to 100% by glufosinate and glyphosate. Glyphosate controlled broadleaf signalgrass, fall panicum, goosegrass, rhizomatous johnsongrass, common lambsquarters, and smooth pigweed at least 90%. Control of these weeds by glyphosate often was greater than control by glufosinate. Mixing fomesafen with glufosinate increased control of these species except johnsongrass. Glufosinate often was more effective than glyphosate on entireleaf and tall morningglories. Fomesafen mixed with glyphosate increased morningglory control but reduced smooth pigweed control. Glufosinate or glyphosate applied sequentially or early postemergence (EPOST) following imazaquin plus SAN 582 PRE often were more effective than glufosinate or glyphosate applied only EPOST. Only rhizomatous johnsongrass was controlled more effectively by glufosinate or glyphosate treatments than by imazaquin plus SAN 582 PRE followed by chlorimuron POST. Yields and net returns with soil-applied herbicides only were often lower than total POST herbicide treatments. Sequential POST herbicide applications or soil-applied herbicides followed by POST herbicides were usually more effective economically than single POST herbicide applications.

Nomenclature: Chlorimuron, ethyl 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl] amino]sulfonyl]benzoate; SAN 582 (proposed name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; fomesafen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-N-(methylsulfonyl)-2-nitrobenzamide; glufosinate, 2-amino-4-(hydroxymethylphosphinyl) butanoic acid; glyphosate, N-(phosphonomethyl)glycine; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #² BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; cutleaf groundcherry, Physalis angulata L. # PHYAN; eclipta, Eclipta prostrata L. # ECLAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; fall panicum, Panicum dichotomiflorum Michx. # PANDI; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia L. Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; soybean, Glycine max (L.) Merr. ‘Asgrow 5403 LL’, ‘Asgrow 5547 LL’, ‘Asgrow 5602 RR’, ‘Hartz 5566 RR’, ‘Southern States FFR 595’.

Additional index words: Herbicide-resistant crops, Liberty Link soybean, nontransgenic soybean, Roundup Ready soybean.

Abbreviations: DAT, days after treatment; EPOST, early postemergence; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; LPOST, late postemergence; POST, postemergence; PRE, preemergence; THR, transgenic, herbicide-resistant; WAA, weeks after late postemergence application; WAP, weeks after planting.

Abstract: Experiments were conducted in 1996 and 1997 in water-seeded and drill-seeded production systems to determine rice response to clomazone applied at rates ranging from 0.28 to 2.2 kg ai/ha on silt loam and silty clay soils. Clomazone-induced bleaching of rice seedlings was 15% or less when clomazone was applied at 0.28 or 0.56 kg/ha. Increasing the rate of clomazone increased bleaching in most experiments. Clomazone at 0.84 kg/ha or higher delayed seed head emergence in five of eight experiments. Clomazone at lower rates did not delay seed head emergence. Although clomazone at 0.28 and 0.56 kg/ha did not reduce grain yield, clomazone at 0.84 and 1.1 kg/ha reduced grain yield in one experiment while clomazone at 1.7 and 2.2 kg/ha reduced yield in two experiments. The influence of soil type and seeding method on rice's tolerance to the microencapsulated formulation of clomazone could not be demonstrated in these experiments. Clomazone was more injurious in drill-seeded production than in water-seeded production.

Nomenclature: Clomazone, 2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone; rice, Oryza sativa L. ‘Cypress’.

Additional index words: Crop injury.

Abbreviations: PRE, preemergence.

Abstract: Leaching and runoff losses of the postemergence-applied herbicide dicamba were evaluated over a 3-yr period (1989 to 1991). Dicamba was applied at the recommended rate (0.56 kg ai/ha) to conventional and mulch tillage planted corn fields on Hagerstown silty clay loam (fine, mixed, mesic Typic Hapludalf). Mulch tillage followed several years of no-tillage corn. Root zone leachates were collected utilizing pan lysimeters placed 1.2 m below the soil surface. Surface runoff was monitored and collected with an HS-flume and automated sampling equipment. Leaching was greatest during 1989, and runoff events were recorded only during this season. Leachate samples containing measurable levels of dicamba were obtained within 21 d of herbicide application or within slightly more than one soil half-life of this chemical. More dicamba leached under mulch tillage than conventional tillage management. Tillage rotation (no tillage to mulch tillage) did not alter the leaching loss potential of dicamba beneath the minimally tilled soil surface, as postulated, compared with the previous untilled surface. The mulch tillage surface reduced runoff water losses compared with conventional tillage, but early-season leaching activity, coupled with the minimal persistence of dicamba in soil, negated runoff transport of this herbicide from either tillage system when the first runoff event occurred 12 d after its application.

Nomenclature: Dicamba, 3,6 dichloro-2-methoxybenzoic acid; corn, Zea mays L.

Additional index words: Leaching, runoff, pan lysimeters.

Abstract: Sulfentrazone dissipation in soil was examined in field experiments in 1995, 1996, and 1997 at Knoxville, TN, on a Sequatchie loam soil. Sulfentrazone 50% disappearance time (DT₅₀) varied from 24 to 113 d. Cotton injury was observed the year following sulfentrazone application when half-lives were ≥85 d. Sulfentrazone degradation under controlled laboratory conditions was slower in autoclaved soil than in nonautoclaved surface soil and subsurface soil, with DT₅₀ of 198, 93, and 102 d, respectively. The difference due to autoclaving the soil implied that sulfentrazone degradation was influenced by both microbial and chemical mechanisms.

Nomenclature: Glyphosate, isopropylamine salt of N-(phosphonomethyl)glycine; pyrithiobac, sodium 2-chloro-6-[(4,6 dimethoxy-2-pyrimidinyl)thio]benzoate; sulfentrazone, N-[2,4-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-1-yl]phenyl]methanesulfonamide; soybean, Glycine max (L.) Merr. ‘Asgrow 5601’; cotton, Gossypium hirsutum L. ‘Paymaster 1220RR’.

Additional index words: Degradation, half-life, HPLC.

Abbreviations: DAT, days after treatment; DT₅₀, 50% disappearance time; HPLC, high performance liquid chromatography; WAT, weeks after treatment.

Abstract: The objectives of this study were to determine the efficacy and risk of controlling weeds at reduced herbicide rates under various environmental and biotic conditions, through analysis of published data on the use of below-labeled rates of herbicides. A database was established by extracting information from previously published papers on weed control at below-labeled rates of herbicides in crop production systems over large geographical and temporal scales. The database was then analyzed to evaluate the efficacy and risk of using herbicides at various reduced rates under different management systems. Using below-labeled herbicide rates in conjunction with interrow cultivation is an effective way of reducing herbicide input in agricultural systems while maintaining satisfactory weed control. There are greater opportunities for herbicide reduction using preemergence (PRE) than preplant incorporated (PPI) or postemergence (POST) herbicides, in coarse-textured than in fine-textured soils, and in corn than in soybean or wheat. The success of reducing herbicide rates does not depend on whether the herbicides are applied in conventional or conservation tillage systems or whether they are used with or without adjuvants. The above conclusions are based on studies conducted in experimental fields where weed pressures may be subjectively chosen to be high. Greater potential for herbicide reduction may exist at locations or in cropping systems were weed pressure is low.

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

Additional index words: Database, herbicides, reduced rates, weed control efficacy.

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

Abstract: Pitted morningglory control with norflurazon or fluometuron preemergence (PRE), each at 1.12 kg/ha, was 72% or less 14 d after a postemergence (POST) application of pyrithiobac in 1993 and 1994. Pyrithiobac POST at 70 g/ha following fluometuron or norflurazon PRE cultivated at any timing controlled pitted morningglory at least 76%. Pyrithiobac POST controlled common cocklebur equal to the weed-free in 1993 at 14 d after the POST application. In 1994, when rated 28 d after pyrithiobac POST, cultivation 3 d before a single application of pyrithiobac controlled less common cocklebur than any other herbicide treatment containing pyrithiobac. At 28 d after pyrithiobac POST, no treatment controlled common cocklebur as well as the weed-free. In 1993 and 1994, seed cotton yield was equal to the weed-free when pyrithiobac followed fluometuron PRE cultivated at any timing or a single application of pyrithiobac cultivated prior to 7 d after POST application.

Nomenclature: Fluometuron, N,N′-dimethyl-N′-[3-(trifluoromethyl)phenyl]urea; norflurazon, 4-chloro-5-(methylamino)-2-(3-(trifluoromethyl)phenyl)-3(2H)-pyridazinone; pyrithiobac, 2-chloro-6-[(4,6-dimethoxy-2-pyrimidinyl)thio] benzoic acid, sodium salt; common cocklebur, Xanthium strumarium L. #³ XANST; pitted morningglory, Ipomoea lacunosa L. # IPOLA; cotton, Gossypium hirsutum L. ‘DES-119’.

Additional index words: Fluometuron, norflurazon, Ipomoea lacunosa, Xanthium strumarium, IPOLA, XANST.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAPA, days after POST application; DBPA, days before POST application; DREC, Delta Research and Extension Center; fb, followed by; IAPA, immediately after POST application; POST, postemergence; PRE, preemergence; PSRC, Plant Science Research Center; SWSRU, Southern Weed Science Research Unit Farm.

Abstract: The impact of Palmer amaranth on mechanical harvesting, ginning, and fiber quality in dryland cotton was documented. Only the highest Palmer amaranth density (3,260 weeds/ha) reduced lint and seed yields. However, all weed densities increased harvesting time 2- to 3.5-fold. Two factors increased the time required for stripper harvesting: slower ground speeds due to large weeds and work stoppages that required hand removal of weed stems lodged in the harvester. Ninety-eight percent of the weedy plant material was discarded in the field by the harvester, and the remaining 2% was successfully removed in ginning and lint-cleaning processes. Weed infestations did not result in any differences in moisture content of seed cotton, ginning time, fiber quality, or the percentage of cleaned lint.

Nomenclature: Cotton, Gossypium hirsutum L.; Palmer amaranth, Amaranthus palmeri S. Wats. #³ AMAPA.

Additional index words: Competition, fiber quality.

Abbreviations: PPI, preplant incorporated.

Abstract: Three commercial formulations of glyphosate were spiked with ¹⁴C-glyphosate and applied via a spray nozzle to velvetleaf plants. The use of ¹⁴C-glyphosate as a marker caused minimal alteration to formulation properties, and the use of spray application simulated field practices. Formulation retention, calculated based on maximum plant-leaf area, showed that only 27 to 33% of the available area retained the spray. The small differences in retention among the formulations suggest that they contribute little to differences in efficacy. Following spray application, plants were harvested at various times to measure the levels of glyphosate uptake into the plant and translocation into roots. Significant differences were observed among the formulations in the rate of glyphosate uptake. The most efficient formulation absorbed about one third of the dose by 24 hr after treatment. Root translocation of glyphosate was approximately proportional to uptake and accounted for less than one third of the absorbed dose. The relationship between uptake and rainfastness was examined in greenhouse studies with simulated rainfall at various times after glyphosate application. A direct correlation was observed between rainfastness with the speed and quantity of glyphosate uptake.

Nomenclature: Glyphosate, N-(phosphonomethyl)glycine. Velvetleaf, Abutilon theophrasti Medik., #³ ABUTH.

Additional index words: Uptake, translocation, retention, track spray, glyphosate formulations.

Abbreviations: DAT, days after treatment; GI, growth inhibition; HAT, hours after treatment.

Abstract: Field experiments were conducted in 1997 and 1998 near Rossville in northeast Kansas to evaluate control of imazethapyr-resistant common sunflower with selected herbicides in corn and soybean. In soybean, common sunflower control was unacceptable with imazethapyr, chlorimuron, CGA-277476, and cloransulam applied alone. Lactofen or acifluorfen applied with these herbicides slightly improved control, whereas glyphosate applied with them controlled more than 97% of common sunflower. All herbicides reduced common sunflower populations in the corn. The greatest reductions occurred when atrazine was applied with dicamba, 2,4-D, RPA 201772, or CGA-152005 plus primisulfuron. These herbicide combinations also stunted common sunflower that survived treatment. Several herbicide alternatives are available to control imazethapyr-resistant common sunflower in corn. However, glyphosate was the only herbicide that gave adequate control in soybean.

Nomenclature: Acifluorfen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid; atrazine, 6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine; CGA-152005, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea; CGA-277476, 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid,3-oxetanyl-ester; chlorimuron, 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino] carbonyl]amino]sulfonyl]benzoic acid; cloransulam, 3-chloro-2-[[(5-ethoxy-7-fluoro[1,2,4]triazolo[1,5-c]pyrimidin-2yl)sulfonyl] amino]benzoic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; glyphosate, N-(phosphonomethyl)glycine; imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; lactofen, (±)-2-ethoxy-1-methyl-2-oxoethyl-5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate; primisulfuron, 2-[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoic acid; RPA 201772, 5-cyclopropyl-4-(2-methylsulphonyl-4-trifluoromethyl-benzoyl)isoxazole; common sunflower, Helianthus annuus L.; corn, Zea mays L. ‘Cargill 6997’; soybean, Glycine max (L.) Merr. ‘Stine 3264’.

Additional index words: Acifluorfen, atrazine, bromoxynil, CGA-152005, CGA-277476, chlorimuron, clopyralid, cloransulam, 2,4-D, dicamba, flumetsulam, glyphosate, imazethapyr, lactofen, metolachlor, primisulfuron, RPA 201772, rimsulfuron, thifensulfuron.

Abbreviations: ALS, acetolactate synthase; DAP, days after planting; DAT, days after treatment.

Abstract: Field studies were conducted under full-season conventional tillage in Delaware and New Jersey to determine the critical time to apply glyphosate with or without residual herbicides for optimum weed control in glyphosate-resistant soybean (GRS). The residual herbicides tank-mixed with glyphosate (0.84 kg/ha) were clomazone (0.55 kg/ha) and imazethapyr (0.063 kg/ha). Herbicide application was made at cracking, unifoliate, and one- to six-trifoliate stages of GRS. Weeds varied in growth stages from preemergence (PRE) at cracking to an average height of 30 cm at the six-trifoliate stage of GRS. Herbicide activity varied by year and weed species. Herbicidal action was better under high (>125 mm/mo) than low (<100 mm/mo) rainfall regime. Glyphosate application without residual herbicides was less effective at cracking and unifoliate than at one- to three-trifoliate leaf stages. Mixing residual herbicides with glyphosate at cracking and unifoliate stages enhanced weed control but made no difference when application was delayed until one- to three-trifoliate stages. For optimum weed control in GRS, the window of application for glyphosate alone was between the one- and three-trifoliate leaf stages, approximately 18 to 28 days after planting (DAP). If glyphosate was tank-mixed with residual herbicides, the window of application extended from cracking until the four-trifoliate stage; and weed interference until the four-trifoliate stage (approximately 32 DAP) did not depress GRS yield.

Nomenclature: Clomazone, 2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone; glyphosate, N-(phosphonomethyl)glycine; imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid.

Additional index words: Critical weed removal period, glyphosate ± residuals, Amaranthus hybridus, Ambrosia artemisiifolia, Chenopodium album, Ipomoea hederacea, Panicum dichotomiflorum, AMACH, AMBEL, CHEAL, IPOHE, PANDI.

Abbreviations: DAP, days after planting; GRS, glyphosate-resistant soybean; POST, postemergence; PRE, preemergence; RAREC, Rutgers Agricultural Research and Extension Center; UD-REC, University of Delaware Research and Education Center.

Abstract: Field studies were conducted in Indiana, Michigan, Ohio, and Wisconsin in 1992 and 1993 to evaluate growth and response of common ragweed (Ambrosia artemisiifolia) to imazethapyr. Plants from ecotypes originating in each state were grown at all four locations. Nontreated plants grown in Wisconsin or Ohio were consistently taller than plants grown in Michigan or Indiana, regardless of the origin of the seeds. Nontreated plants originating from Wisconsin or Michigan showed a trend toward flowering earlier than those originating from Indiana or Ohio, regardless of test site. The results suggest the existence of common ragweed ecotypes based on origin of the seeds. Weather conditions after treatment with imazethapyr had a greater influence on common ragweed control and regrowth than the origin of common ragweed seeds. Common ragweed regrew following imazethapyr application through the development of axillary buds under conditions of warm temperatures and moist soils during the 4 to 6 wk following imazethapyr application. Mild to cool temperatures or dry conditions following imazethapyr application reduced treated common ragweed regrowth. Both early- and mid-postemergence imazethapyr treatments delayed flowering of all ecotypes. However, flowering of imazethapyr-treated plants followed the same order as nontreated plants, with plants from the Michigan or Wisconsin ecotypes showing a trend toward flowering earlier than those from Indiana or Ohio.

Nomenclature: Imazethapyr, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid; common ragweed, Ambrosia artemisiifolia L. #³ AMBEL.

Additional index words: Environmental conditions, weed ecotype, AMBEL.

Abbreviations: EPOST, early postemergence; MPOST, mid-postemergence; WAT, weeks after treatment.

Abstract: In greenhouse experiments, Ohio accessions of 22 weed species representing 13 dicot families were screened as alternative hosts of soybean cyst nematode (SCN, Heterodera glycines). Purple deadnettle (Lamium purpureum), henbit (Lamium amplexicaule), field pennycress (Thlaspi arvense), shepherd's-purse (Capsella bursa-pastoris), and a susceptible soybean (Glycine max) cultivar produced SCN population densities of 510, 155, 73, 1, and 366 cysts/450 cm³ soil, respectively, 5 wk after inoculation with eggs from a race 3 SCN population. Purple deadnettle was also a strong host of race 1 SCN and a weak host of race 6 SCN. Average numbers of eggs/cyst among race 3 hosts were highest in purple deadnettle (357), followed by soybean (292), field pennycress (266), henbit (122), and shepherd's-purse (none detected). To our knowledge, henbit is the only SCN host identified here that has been previously identified as a host. The weeds identified as SCN hosts in this study have a winter annual life cycle in Ohio and may serve as sites for SCN reproduction in infested fields during the early or late growing season and when soybean plants are absent.

Nomenclature: Field pennycress, Thlaspi arvense L. #³ THLAR; henbit, Lamium amplexicaule L. # LAMAM; purple deadnettle, Lamium purpureum L. # LAMPU; shepherd's-purse, Capsella bursa-pastoris (L.) Med. # CAPBP; soybean, Glycine max (L.) Merr. ‘Corsoy 79’; soybean cyst nematode, Heterodera glycines Ichinohe.

Additional index words: Alternate hosts, integrated weed management, CAPBP, LAMAM, LAMPU, THLAR.

Abbreviations: SCN, soybean cyst nematode.

Abstract: Field studies were conducted from 1996 to 1998 to evaluate grass control in no-till corn (Zea mays) with herbicides applied early preplant (EPP), preemergence (PRE), and postemergence (POST) at the Belleville Research Center at Belleville, IL. Grass control was affected by application timing rather than herbicide. The herbicides applied PRE provided more consistent giant foxtail (Setaria faberi) and barnyardgrass (Echinochloa crus-galli) control (90 to 98%) than the same herbicides applied EPP (0 to 92%). There also was no difference in giant foxtail and barnyardgrass control between the emulsifiable concentrate (EC) formulation and microencapsulated (ME) formulation of acetochlor. Rimsulfuron plus thifensulfuron applied POST provided 90 to 97% control of giant foxtail and barnyardgrass. Metolachlor, EC-acetochlor, SAN 582H, and rimsulfuron plus thifensulfuron provided 85 to 92% control of yellow nutsedge (Cyperus esculentus) compared with 63 to 74% control for BAY FOE 5043 plus metribuzin and ME-acetochlor. Corn grain yield was greater with herbicides applied either PRE or POST than applied EPP. Grass control and grain yield were greater with herbicides applied either PRE or POST compared with EPP.

Nomenclature: Acetochlor, 2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide; BAY FOE 5043 (proposed name, flufenacet), N-(4-fluorophenyl)-N-(1-methylethyl)-2-[[5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl]oxy]acetamide; metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one; rimsulfuron, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(ethylsulfonyl)-2-pyridinesulfonamide; SAN 582H (proposed name, dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl) acetamide; thifensulfuron, 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] amino]sulfonyl]-2-thiophenecarboxylic acid; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; giant foxtail, Setaria faberi Herrm. # SETFA; yellow nutsedge, Cyperus esculentus L. # CYPES; corn, Zea mays L. ‘Pioneer 3335’.

Additional index words: Early preplant, preemergence, postemergence.

Abbreviations: DAP, days after planting; EC, emulsifiable concentrate formulation; EPP, early preplant; ME, microencapsulated formulation; POST, postemergence; PRE, preemergence.

Abstract: Knowledge of optimal combinations of graminicide rate and stage of application could improve the effectiveness and net benefit of commonly used graminicides. A study was conducted at two locations in Saskatchewan, Canada, from 1994 to 1997. Factorial combinations of five graminicides (CGA 184927, fenoxaprop-p-ethyl, ICIA 0604, imazamethabenz, and flamprop-methyl), three graminicide rates (full, two-thirds, and one-third recommended label rate), and three leaf stages of wild oat (Avena fatua; two-, four-, and six-leaf) were compared to determine their effect on wild oat fresh weight, wheat (Triticum aestivum) seed yield, and net return. Wild oat fresh weight increased and wheat seed yield decreased to a greater extent at Saskatoon (median wild oat fresh weight of 56 g/m²) than at Scott (median wild oat fresh weight of 85 g/m²) when graminicide rate was reduced from the recommended label rate. Net return consistently decreased at both locations and among all graminicides when application rate was reduced from two-thirds to one-third of the recommended label rate. Imazamethabenz applied at progressively later growth stages caused greater wild oat fresh weight at both locations and reduced wheat yield and net return. Applying other graminicides at the earliest (two-leaf) stage of wild oat generally resulted in more or similar levels of wild oat fresh weight compared with delayed applications, especially at Saskatoon. With the exception of imazamethabenz, crop yield and net return were unaffected by leaf stage at both locations. The optimal graminicide rate is mostly dependent on the level of wild oat infestation, and the best time to control wild oat is dependent mostly on the particular graminicide.

Nomenclature: CGA 184927 (proposed common name, clodinafop propargyl), 2-propynyl-(R)-2-[4-(5-chloro-3-fluoro-2-pyridyloxy)-phenoxy]-propionate; fenoxaprop-p-ethyl, (±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy]phenoxy]propanoic acid; flamprop-methyl, N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine; imazamethabenz, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4(and 5)-methylbenzoic acid (3:2); ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #³ AVEFA; hard red spring wheat, Triticum aestivum L. ‘CDC Makwa’ and ‘CDC Teal.’

Additional index words: Graminicides, leaf stage, application parameters, weed interference, economic return.

Abstract: Several graminicides were evaluated at various application timings for control and seedhead suppression of red rice (Oryza sativa) in soybean (Glycine max). One application of clethodim, fluazifop-P, quizalofop-P, or sethoxydim at any timing did not control red rice more than 86% 2 wk after treatment. Emergence of red rice seedlings subsequent to applications reduced control later in the season. At a naturally infested location, seedhead reduction was greatest, regardless of graminicide, when application was delayed until the four-leaf stage. At a second location, seedhead reductions were highest following graminicide applications at the two-leaf stage of growth. No single graminicide application completely eliminated red rice seedhead production. Soybean yields were reduced when graminicide application was delayed until the boot stage at both locations, and following two-leaf stage applications at the naturally infested location.

Nomenclature: Clethodim, (E,E)-(±)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]propyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; fluazifop-P, (R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid; quizalofop-P, (R)-2-[4-[(6-chloro-2-quinoxalinyl)oxy]phenoxy]propanoic acid; sethoxydim, 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one; red rice, Oryza sativa L. #³ ORYSA; soybean, Glycine max (L.) Merr. ‘Hartz 4464’ and ‘Terra-Vig 5452’.

Additional index words: Clethodim, fluazifop-P, quizalofop-P, sethoxydim, ORYSA.

Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAT, weeks after treatment.

Abstract: Site-specific herbigation using a linear-move irrigation system equipped with an automated irrigation control system was evaluated in a series of field trials conducted at the University of Idaho Aberdeen Research and Extension Center near Aberdeen, ID. In the first study, the experimental area was divided into site-specific management zones that were randomly assigned herbigation treatments of metolachlor at 0, 1.8, 2.7, or 3.6 kg ai/ha. In a second study, site-specific herbigation treatments of metribuzin at 0, 0.28, 0.42, or 0.56 kg ai/ha were applied. The tests covered a range in system flow rate from 29 to 90% of maximum design flow. Average metolachlor rates applied were within 1, 2, and 4% of the target 1.8, 2.7, and 3.6 kg/ha rates, respectively, and average metribuzin rates were on target at the 0.28 kg/ha rate and within 5 and 2% of the 0.42 and 0.56 kg/ha target rates, respectively. In a third study, potato (Solanum tuberosum) fields were divided into management zones, and low, medium, or high populations of Indian mustard (Brassica juncea) and foxtail millet (Setaria italica) were seeded in each zone. Different rates of a metolachlor plus metribuzin mixture were herbigated in each zone—higher rates in zones with high populations and lower rates in zones with low populations. Weed control was excellent in all zones. Results suggest good potential for site-specific herbigation when linear-move or center-pivot irrigation systems are equipped with the automated irrigation control system.

Nomenclature: Metolachlor, 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide; metribuzin, 4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5-(4H)-one; Indian mustard, Brassica juncea (L.) Czern. et Coss. #³ BRSJU ‘Common Brown’; foxtail millet, Setaria italica (L.) Beauv. # SETIT; potato, Solanum tuberosum L. ‘Russet Burbank’ # SOLTU.

Additional index words: Chemigation, herbicide application, precision agriculture, variable-rate application technology, Chenopodium album, Amaranthus retroflexus, AMARE, CHEAL.

Abbreviations: CV, coefficient of variation; DF, dry flowable; EC, emulsifiable concentrate.

Abstract: Woollyleaf bursage (Ambrosia grayi) is a noxious, rhizomatous perennial with an extensive creeping root system. It is found in the central and southern Great Plains of the U.S. Clopyralid alone or fluroxypyr, picloram, or glyphosate with either 2,4-D or dicamba were applied to woollyleaf bursage at anthesis and 30 d later in three field experiments. With the exception of treatments containing picloram, the effect of application timing was inconsistent. All treatments containing picloram consistently controlled woollyleaf bursage 93% or greater for 9 mo and 74% or greater for 11 mo. Control was poor or inconsistent with all other treatments. Although a rate response was seen with clopyralid, a level higher than 0.28 kg/ha may be necessary to control woollyleaf bursage. After 11 mo, control was less than 60% with treatments containing 1.7 kg/ha of glyphosate in 10 of 12 herbicide treatments and timing combinations over 3 yr.

Nomenclature: Clopyralid, 3,6-dichloro-2-pyridinecarboxylic acid; dicamba, 3,6-dichloro-2-methoxybenzoic acid; fluroxypyr, [(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid; glyphosate, N-(phosphonomethyl)glycine; picloram, 4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid; 2,4-D, (2,4-dichlorophenoxy)acetic acid; woollyleaf bursage, Ambrosia grayi (A. Nels.) shinners #³AMBGR.

Additional index words: Woollyleaf franseria, bur ragweed, perennial weed control.

Abstract: Diuron, simazine, and terbacil were applied in field plots annually from 1981 to 1995. Soil was sampled at selected times after herbicide application in 1993, 1994, and 1995 to determine herbicide residue changes with time and soil depth. Diuron residues were found mainly in the upper 20 cm of soil; residue concentration decreased exponentially with time. Less than 1% of the initial concentration after application in summer was present the following spring. Terbacil residues were found in soil below the upper 20 cm. Terbacil degraded more slowly than diuron, and residues in spring were less than 30% the level of the previous summer. Simazine plus hydroxysimazine soil residues were present in all depths to 100 cm and were higher than diuron or terbacil at these depths. Simazine plus hydroxysimazine residues in spring were nearly 40% the level of the previous summer. With all three herbicides, soil residues were greatest in the upper 20 cm of soil during 2 to 3 wk following application. Data confirmed that diuron did not leach, whereas simazine can migrate through the soil. Terbacil migrated intermediately in depth relative to diuron and simazine. After 15 annual applications, herbicide residues were present but were not accumulating.

Nomenclature: Diuron, N′-(3,4-dichlorophenyl)-N,N-dimethylurea; simazine, 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine; desethylsimazine, 2-chloro-4-(ethylamino)-6-amino-s-triazine; di-desethylsimazine, 2-chloro-4,6-diamino-s-triazine; hydroxysimazine, 2-hydroxy-4,6-bis(ethyl-amino)-s-triazine; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione.

Additional index words: Herbicide movement.

Abbreviations: DAT, days after herbicide treatment; GC-MS, gas chromatography–mass spectrometry; HPLC-PDA, high-performance liquid chromatography with photodiode array detector; MS, mass spectrometry; ODS, octadecyl silane; SFE, supercritical fluid extraction.

Abstract: Diuron, simazine, and terbacil were applied together or separately in the field each May from 1981 through 1996. Weed control was over 90% in 1981 and 1982, but by 1984 weeds increased in plots treated with diuron and simazine. Weed abundance was relatively low from 1981 through 1996 in plots treated with terbacil. Broadleaf and grass species abundance was similar in most herbicide-treated plots from 1992 through 1996. Perennial species, particularly fescue (Festuca arundinacea) and ailanthus (Ailanthus altissima), dominated sites treated with diuron and simazine. The weed community changed within 3 yr of the implementation of the weed management program that relied solely on herbicides. A relatively stable weed community persisted from 1992 through 1996. Repeated use of the combined high rate of diuron and low rate of terbacil provided excellent weed control for 15 yr.

Nomenclature: Diuron, N′-(3,4-dichlorophenyl)-N,N-dimethylurea; simazine, 6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine; terbacil, 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione; ailanthus, Ailanthus altissima (Mill.) Swingle. #³ AILAL; tall fescue, Festuca arundinacea Schreb. # FESAR.

Additional index words: Fruit orchards, selection, weed shifts, cheat, poison ivy, johnsongrass, yellow foxtail.

Abstract: A field study was conducted over 2 yr to compare efficacy and economics of glyphosate-resistant, sulfonylurea-tolerant, and conventional soybean (Glycine max) weed control programs. Herbicide programs in the three soybean systems provided at least 90% control of browntop millet (Brachiaria ramosa), prickly sida (Sida spinosa), yellow nutsedge (Cyperus esculentus), pitted morningglory (Ipomoea lacunosa), and hemp sesbania (Sesbania exaltata) in most cases and postemergence (POST)-only programs were as effective as preemergence (PRE) followed by POST programs. Control of hyssop spurge (Euphorbia hyssopifolia) ranged from 93 to 100% in glyphosate-resistant soybean and from 88 to 100% in conventional soybean, but control was 60 to 100% in sulfonylurea-tolerant soybean. Sicklepod (Senna obtusifolia) control was at least 91% in glyphosate-resistant and sulfonylurea-tolerant soybean but was 81% for the standard SAN 582 plus imazaquin PRE and acifluorfen plus bentazon early POST treatment in conventional soybean. In glyphosate-resistant soybean, glyphosate applied sequentially resulted in an average yield of 3,020 kg/ha with a net return of $407/ha. In sulfonylurea-tolerant soybean, chlorimuron applied sequentially yielded 2,500 kg/ha with a net return of $271/ha. Conventional soybean yield with the standard herbicide program was 2,770 kg/ha with a net return of $317/ha. Yields for the cultivars were equivalent when the same standard herbicide program was used. When weed control is satisfactory and herbicide costs relatively comparable, yield potential of the cultivar and seed cost, including any technology fee, would be key factors in selecting a weed management system.

Nomenclature: Acifluorfen, 5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid; bentazon, 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide; chlorimuron, 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid; glyphosate, N-(phosphonomethyl) glycine; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imadazol-2-yl]-3-quinolinecarboxylic acid; SAN 582 (proposed common name, dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide; browntop millet, Brachiaria ramosa (L.) Stapf #³ PANRA; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W. Hill # SEBEX; hyssop spurge, Euphorbia hyssopifolia L. # EPHHS; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; soybean, Glycine max (L.) Merr. ‘DP 5806 RR,’ ‘DP 3571 S,’ ‘DP 3588.’

Additional index words: CASOB, CYPES, EPHHS, IPOLA, PANRA, SEBEX, SIDSP.

Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; POST, postemergence; PRE, preemergence; WAP, weeks after planting.

Abstract: Studies were conducted to determine effects of preharvest applications of glyphosate on the seed and seedling quality of ‘Alpowa’ and ‘Penawawa’ soft white spring wheat (Triticum aestivum) varieties. Glyphosate was applied at 0.62 or 0.84 kg ae/ha at the milk (Zadoks' scale 70 to 79), soft dough (Zadoks' scale 85), or hard dough stage (Zadoks' scale 87) of wheat development; 7 d following the hard dough treatment; and 1 d prior to wheat harvest. In harvest aid applications, wheat yields were reduced only with glyphosate applied at the milk stage of development. Yield reduction ranged from 20 to 77% depending on the year, variety, and glyphosate rate. Likewise, kernel weight and germination were affected only by glyphosate applications at the milk stage with reductions from 19 to 73% and from 2 to 46% for kernal weight and percent germination, respectively, compared to untreated wheat. Using wheat from harvest-aided glyphosate treatments at the milk stage as seeds the following year resulted in reductions ranging from 28 to 99%, 19 to 39%, and 12 to 97% for seedling density, plant height, and seed yield, respectively, compared to seeds from untreated wheat. In this study, wheat seed and seedling quality following preharvest glyphosate applications were most greatly influenced by crop maturity stage at time of application than by herbicide rate or variety.

Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; spring wheat, Triticum aestivum L. ‘Alpowa,’ ‘Penewawa.’

Additional index words: Desiccation, germination, harvest aid, herbicide.

Abstract: Field studies were conducted in 1994 and 1995 to evaluate CGA-152005 for weed control and effect on peanut (Arachis hypogaea) yield in Texas peanut production areas. CGA-152005 at 10 to 20 g/ha controlled eclipta (Eclipta prostrata), golden crownbeard (Verbesina enceliodes), and Palmer amaranth (Amaranthus palmeri) > 90% when applied preemergence (PRE) or soon after peanut emergence (EPOST). CGA-152005 postemergence (POST) controlled eclipta > 95%; sandhills amaranth (Amaranthus arenicola) 99%; golden crownbeard, pitted morningglory (Ipomoea lacunosa), and hophornbeam copperleaf (Acalypha ostryifolia) < 80%; and Palmer amaranth and ivyleaf morningglory (Ipomoea hederacea) from 37 to 89%. CGA-152005 injured peanut up to 37% and reduced yield up to 94%.

Nomenclature: CGA-152005 (proposed common name prosulfuron), 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoroprophyl)phenylsufonyl]urea; eclipta, Eclipta prostrata L. #³ ECLAL; golden crownbeard, Verbesina enceliodes (Cav.) Benth et Hook # VEREN; hophornbeam copperleaf, Acalypha ostryifolia Riddell # ACCOS; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sandhills amaranth, Amaranthus arenicola I.M. Johnst. # AMAAR; peanut, Arachis hypogaea L. ‘GK-7.’

Additional index words: Groundnut, preemergence, postemergence, weed management.

Abbreviations: EPOST, early postemergence; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Abstract: Effective methods are needed to eradicate tall fescue (Festuca arundinacea) and convert tall fescue fields into habitats more suitable to wildlife species. The objectives of this study were to determine the efficacy of (1) a single glyphosate application during the spring or fall and (2) AC 263,222, alone and in combination with glyphosate, applied during four different tall fescue growth stages for control of established tall fescue. Studies were conducted during 1996 to 1998 in fields dominated by tall fescue located in central Kentucky. Pre- and posttreatment plant communities were described to quantify differences in vegetative characteristics due to herbicide applications. Glyphosate at 2.2 kg ai/ha applied during the spring or fall was effective in reducing tall fescue to less than 12% cover. AC 263,222 at 0.2 kg ai/ha, AC 263,222 at 0.2 kg/ha plus glyphosate at 0.6 kg/ha, or AC 263,222 at 0.2 kg/ha plus glyphosate at 1.1 kg/ha applied during the spring growth, boot, summer dormancy, and fall growth stages were equally effective, reducing tall fescue cover to less than 3% at 2 to 7 mo after treatment. Glyphosate and AC 263,222 are effective tools for the initial removal of tall fescue.

Nomenclature: AC 263,222, (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid; glyphosate, N-(phosphonomethyl)glycine; tall fescue, Festuca arundinacea Schreb. #³ FESAR.

Additional index words: Fescue conversion.

Abbreviations: NWSG, native warm-season grasses; OM, organic matter; SE, standard error of the mean; MAT, months after treatment.