Fall applications of fenarimol on hybrid Bermudagrass (Cynodon dactylon × C. transvaalensis) provide effective preemergence Poa annua (L.) control and suppress Ophiosphaerella spp. pathogens; however, concerns exist for turf injury and root growth restrictions. Two 60-d greenhouse studies were conducted to evaluate the effects of fenarimol at 0, 1.6, and 3.2 kg ai/ha per 30 d with and without trinexapac-ethyl (TE) at 0.017 kg ai ha/15 d on ‘TifEagle’ Bermudagrass. Turf color was enhanced by TE 14 d after initial treatment (DAIT) and was continually superior throughout the experiment. Fenarimol at 3.2 kg/ha per 30 d decreased turf color 14 DAIT, but was similar to nontreated turf on all other observation dates. Increased fenarimol rates applied twice caused approximately 10% injury at 42, 49, and 56 d after treatment; however, injury was acceptable after initial and repeat applications. TE reduced clipping yield an average 39% from six sampling dates. Initial fenarimol applications (without TE) reduced clippings by 37% 20 DAIT and repeated applications reduced clippings 40, 50, and 60 DAIT. Increased fenarimol rate linearly decreased root mass for turf treated with and without TE; however, Bermudagrass receiving TE averaged 23% enhanced root mass 60 DAIT over all fenarimol rates. Bermudagrass receiving fenarimol at 0, 1.6, and 3.2 kg/ ha per 30 d with TE averaged 27, 24, and 16% higher root mass, respectively, compared to turf receiving fenarimol without TE. Treatments had no influence on root length. Results indicate that two consecutive fenarimol applications at 1.6 and 3.2 kg/ha per 30 d may cause minor injury to TifEagle Bermudagrass and restrict root growth. Repeated TE applications, however, could decrease injury from fenarimol and enhance rooting relative to fenarimol applied exclusively.

Nomenclature: Annual bluegrass, Poa annua L.; fenarimol, [2-(2-chlorophenyl)-2-(4-chlorophenyl)-5-pyrimidinemethanol]; spring dead spot, Ophiosphaerella spp.; trinexapac-ethyl, [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester].

Additional index words: Fungicides, golf courses, plant growth regulators, PGRs, root growth, turfgrass.

Field studies were conducted at three locations to evaluate glyphosate-resistant (GR) cotton response, weed control, and cotton lint yields to two formulations of glyphosate (diammonium salt– glyphosate and isopropylamine salt–glyphosate) and trifloxysulfuron applied early postemergence (EPOST) alone or to tank mixtures of trifloxysulfuron with each glyphosate formulation, with and without a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA. Trifloxysulfuron and both formulations of glyphosate controlled common lambsquarters and pitted morningglory. Both glyphosate formulations provided equivalent control of common lambsquarters, goosegrass, pitted morningglory, prickly sida, and smooth pigweed. Trifloxysulfuron controlled smooth pigweed better than either glyphosate formulation but did not control goosegrass or prickly sida. Prometryn plus MSMA LAYBY improved late-season control of common lambsquarters, goosegrass, large crabgrass, and pitted morningglory for all EPOST systems and improved late-season smooth pigweed control for EPOST systems that did not include trifloxysulfuron. Cotton injury was 2% or less from both glyphosate formulations, while trifloxysulfuron injured ‘Deltapine 5415RR’ 7 to 16% at two locations. At a third location, trifloxysulfuron injured ‘Paymaster 1218RR/BG’ 24%, and when applied in mixture with either glyphosate formulation, injury increased to at least 72%. Cotton injury was transient at the first two locations and was not visually apparent 3 to 5 wk later. Cotton yield at the third location was reduced. High cotton yields reflected high levels of weed control.

Nomenclature: Glyphosate; MSMA; prometryn; trifloxysulfuron; common lambsquarters, Chenopodium album (L.) Roth #³ CHEAL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa Gray # IPOLA; prickly sida, Sida spinosa L. # SIDSP; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Paymaster 1218RR/BG’, ‘Deltapine 5415RR’.

Additional index words: Diammonium salt, isopropylamine salt.

Abbreviations: DIA, diammonium salt of glyphosate; IPA, isopropylamine salt of glyphosate; POT, postemergence over the top.

In the state of Illinois, waterhemp and smooth pigweed are among the worst agricultural weeds. Previous research shows high potential for hybridization between these two species. However, the actual occurrence of hybrids in natural settings is still uncertain. Morphological similarity between hybrids and waterhemp makes field surveys of hybrids difficult to conduct. The main purpose of this study was to characterize the morphology of waterhemp × smooth pigweed F₁ hybrids, emphasizing evaluation of characters that may allow for hybrid discrimination in field Amaranthus communities. Concurrently, the study characterized hybrid reproductive fitness, chromosome number, and DNA content. To accomplish this, hybrids were obtained from field crosses. A species-specific polymorphism in the ALS gene was used to verify hybrid identity. Significant differences (α = 0.05) between hybrids and individuals of the parental species were observed for five staminate and five carpellate characters. Of these, five characters differentiated hybrids from waterhemp. However, clustering analyses using these characters indicated that morphological differences were not reliable enough, by themselves, for unambiguous hybrid identification. Also, hybrid homoploidy (2n = 32) with respect to parental species excluded chromosome counts in hybridity determinations. However, DNA content analysis may be used for such purpose. Hybrids had an average of 1.21 pg of DNA per 2C nucleus, a value intermediate to that of parental species. Hybrids produced 3.3 or 0.7% the seed output of parental and sibling waterhemp individuals, respectively. Percent micropollen in hybrids was 95-times greater than in parental species. Hybrid sterility appears to be the most reliable feature for hybrid discrimination when conducting field surveys. However, molecular and cytogenetic analyses as employed in this study may be desired for ultimate identity corroboration.

Nomenclature: Common waterhemp, Amaranthus rudis Sauer #³ AMATA; smooth pigweed, Amaranthus hybridus L. # AMACH; tall waterhemp, Amaranthus tuberculatus (Moq.) Sauer # AMATU.

Additional index words: Gene flow, evolution, herbicide resistance.

Abbreviations: ALS, acetolactate synthase (EC 2.2.1.6); PCR, polymerase chain reaction.

Field experiments were conducted at Hays and Manhattan, KS, in 2002 and 2003 to determine winter wheat response to simulated drift rates of glyphosate and imazamox. Glyphosate and imazamox at 1/100×, 1/33×, 1/10×, and 1/3× of usage rates of 840 g ae/ha glyphosate and 35 g/ha imzamox were applied individually to wheat in the early jointing or the early flower stages of growth. Wheat injury and yield loss increased as herbicide rate was increased, with minimal effect from either herbicide at the 1/100× rate, and nearly complete kill and yield loss of wheat from both herbicides applied at the 1/3× rate, regardless of growth stage at application. In general, wheat injury and yield reduction were greater from glyphosate than from imazamox. In addition, wheat injury and yield loss were greater from herbicide treatment at the jointing stage than at the flowering stage of development. Correlation analysis suggests that visual injury is an accurate indicator of yield reductions. Germination tests of harvested grain showed that the viability of the wheat seed was not reduced if plants survived the herbicide treatment and produced a harvestable seed.

Nomenclature: Glyphosate; imazamox; wheat, Triticum aestivum L.

Addition index words: Crop injury, herbicide drift, herbicide symptoms, yield reduction.

Abbreviations: WAT, weeks after treatment.

Perennial pepperweed is an invasive weed spreading rapidly throughout a wide range of habitats in the western United States. This study was designed to test whether integrating early season mowing with a systemic herbicide application would improve the control of perennial pepperweed. Experiments were conducted within three different environments including high desert, roadside, and floodplain areas. In treatments not mowed, chlorsulfuron at 0.104 kg ai/ha reduced perennial pepperweed biomass and density by 100%, whereas applications of 2,4-D at 2.11 kg ae/ha and glyphosate at 3.33 kg ae/ha were inconsistent and did not provide effective control. Mowing alone did not reduce perennial pepperweed biomass or density the following year, but mowing followed by application of a herbicide treatment to resprouting plants reduced biomass at all three sites compared with nonmowed treatments including herbicides. Among combinations of mowing and herbicides, chlorsulfuron at 0.052 kg/ha reduced perennial pepperweed biomass by >99% at all three sites, and glyphosate at 3.33 kg/ha reduced biomass by ≥80% at two sites 1 yr after applications. The effectiveness of glyphosate at 3.33 kg/ha in combination with mowing provides land managers with a valuable control option for perennial pepperweed in wetland or riparian areas where chlorsulfuron is not registered for use.

Nomenclature: Chlorsulfuron; glyphosate; 2,4-D; perennial pepperweed, Lepidium latifolium L. #³ LEPLA.

Additional index words: Invasive weed, herbicide, riparian, herbaceous perennial.

Abbreviations: YAT, year after treatment.

Field studies were conducted from 2000 to 2003 to determine the effectiveness of potato desiccants for late-season hairy nightshade control and also their effect on hairy nightshade seed germination. Commercial sulfuric acid at 280 L/ha controlled 94 to 99% of the hairy nightshade 1 wk after treatment (WAT) in all years. Diquat at 560 g/ha and glufosinate-ammonium at 420 g/ha provided at least 93% control 1 WAT in all years except 2003 when control did not exceed 72%. By 3 WAT, hairy nightshade control ranged from 93 to 100% for all treatments, including carfentrazone-ethyl at 56 g/ha, diquat at 420 g/ha, paraquat at 530 g/ha, and sulfuric acid (proprietary process) at 280 L/ha. Treatment of plants with desiccants did not affect germination of hairy nightshade seed, with the exception of a 7% reduction in germination by the higher rate of diquat in 2001 and 2002.

Nomenclature: Carfentrazone-ethyl; diquat; glufosinate-ammonium; paraquat; sulfuric acid; Solanum sarrachoides Sendter #³ SOLSA; potato, Solanum tuberosum L.

Additional index words: Desiccation; potato vine-kill; weed seed germination.

Abbreviations: AMS, ammonium sulfate; MSO, methylated seed oil; NIS, nonionic surfactant; WAH, weeks after harvest.

Crop yield and weed control rating have been used to measure weed and crop response to weed management treatments, eliminate unacceptable weed management treatments, and select “best” treatments for recommendation to farmers. However, the mathematical relationship between crop yield and rated weed control has not been reported before from such treated screening experiments. Likewise, differences have not been reported before in rated weed control among experienced observers (i.e., reliability) when rating the same experiments and for an experienced observer over time (i.e., repeatability). Data from published experiments on zone herbicide application in field corn in which weeds reduced yield to various amounts were reanalyzed to examine these issues. For this study, relative corn yield was calculated as a percentage of the 1× broadcast herbicide rate for two observers and either three experimental site-years or their average. For observer A, relative corn yield (%) increased linearly as rated total weed control (%) increased for all 3 site-yr and their average. For observer B, equations were curvilinear in 2 of 3 site-yr. For both observers, equations accounted for little data variability in relative corn yield (r² = 0.25 and 0.25 in site-year 1, respectively, 0.38 and 0.36 in site-year 2, 0.58 and 0.57 in site-year 3, and 0.43 and 0.42 for their average). When rated total weed control by observer A was graphed against that of observer B, the relationship was a nearly ideal 1:1 linear relationship in only 1 of 3 site-yr. In two other site-years, equations were nonlinear, indicating that one observer distinguished smaller differences between treatments at lower rated control than the other observer. Between-row total weed cover and in-row total weed height influenced observer weed control rating.

Nomenclature: Corn, Zea mays (L.) #³ ZEAMX ‘Pioneer 33G28’.

Additional index words: Rating; weed, Setaria faberii (L.) Beauv. # SETFA, Amaranthus rudis Sauer. # AMATA.

Abbreviations: IR, in-row; BR, between-row; ZHA, zone herbicide application.

Tall ironweed is a troublesome perennial weed that infests cool-season grass pastures in Kentucky. Field experiments were conducted in 2000 through 2003 to evaluate the efficacy of fall-applied herbicides on established tall ironweed following a midsummer mowing. Triclopyr-containing treatments showed the greatest suppression of tall ironweed 12 mo after treatment (MAT), across all years. With triclopyr at 0.56 and 0.63 kg/ha, tall ironweed control was 80% or greater in 2 of the 3 yr. Dicamba initially provided 87% control 8 MAT in 2 of 3 yr and declined to less than 60% 12 MAT. Tall ironweed shoot density was also reduced 66% or more 12 MAT with fall-applied triclopyr-containing treatments. In contrast, tall ironweed density increased approximately twofold in dicamba-treated plots between 8 to 12 MAT in all 3 yr. The impact of herbicide treatment on dry matter (DM) yield of spring-seeded red clover (Trifolium pratense L.), tall ironweed, and forage grasses was also evaluated. Red clover DM yield in the herbicide-treated plots in 2002 showed no significant differences from the untreated control. However, red clover DM yield in 2003 was lowest for the two triclopyr clopyralid treatments, indicating a decrease in DM production compared with that of the nontreated control. Results indicated that fall-applied triclopyr-containing herbicides following a midsummer mowing is an effective program for removing tall ironweed from grass pastures, but further research is needed to evaluate the establishment of red clover following herbicide treatment.

Nomenclature: Clopyralid; dicamba; triclopyr; tall ironweed, Vernonia altissima Nutt. #³ VENAL; red clover, Trifolium pratense L. ‘Kenland’.

Additional index words: Fall application, grass pasture, mowing, perennial dicots, VENAL.

Sand stockpiles, located near commercial cranberry beds in Massachusetts, New Jersey, Washington, and Wisconsin, were sampled quarterly over a 2-yr period. Samples were collected from the surface and the interior of the piles. Utilizing a simple greenhouse germination bioassay, 74 plant species representing 23 plant families were identified across all locations and samples. Plant density varied by region and by sampling depth; species richness varied by region only. More seedlings germinated from samples taken from the surface of the stockpile compared with interior samples. Almost half of all species detected in either surface or interior samples were represented by only one seedling. Fifty-nine percent of the plant species from Massachusetts and New Jersey samples, and 79% and 96% of the plant species from Wisconsin and Washington, respectively, were considered to be weeds in cranberry production. Only one-third of the identified species had wind-blown seeds; seed dispersal was by other mechanisms in almost half of the species. This survey documented the weed management implications of spreading stockpiled sand on cranberry bogs for horticultural or pest management purposes. To minimize the introduction of additional weed problems, growers and integrated pest management consultants should evaluate the seedbank potential of a stockpile prior to application of the sand to the production area.

Nomenclature: Cranberry, Vaccinium macrocarpon Ait.

Additional index words: Integrated weed management, cultural practices, seedling emergence, germination, weed seed dispersal, seedbank dynamics.

Sunflower lines developed to resist some acetolactate synthase (ALS)-inhibiting herbicides are susceptible to foliar applications of other ALS-inhibiting herbicides. Research was conducted to determine whether imidazolinone (IMI)- or sulfonylurea (SU)-resistant sunflower was affected by soil residues of imazethapyr, metsulfuron, or flucarbazone. In greenhouse experiments, IMI-sunflower displayed 60 and 66% injury 4 wk after emergence with incorporated soil residues of metsulfuron at 4.2 g ai/ha and flucarbazone at 30 g ai/ha, respectively, but response to imazethapyr at 35 g ai/ ha was not different from that of nontreated plants. Metsulfuron at 4.2 g/ha and flucarbazone at 30 g/ha resulted in 56 and 72% less biomass accumulation, respectively, of IMI-sunflower compared with that of nontreated plants. Incorporated soil residues of imazethapyr, metsulfuron, or flucarbazone did not cause significant injury or result in shorter plants or less biomass accumulation of SU-sunflower than nontreated sunflower in greenhouse experiments. In field experiments, nonincorporated residues of imazethapyr, metsulfuron, or flucarbazone did not induce visible chlorosis or significant stunting of IMI- or SU-sunflower compared with nontreated sunflower. Herbicide-resistant sunflower growing in soil with nonincorporated residues of imazethapyr, metsulfuron, or flucarbazone produced seed yield similar to sunflower growing in sulfentrazone-treated soil or nontreated soil.

Nomenclature: Flucarbazone; imazethapyr; metsulfuron; sulfentrazone; sunflower, Helianthus annuus L. ‘DeKalb DKF 29-90’, ‘Mycogen 81359’, ‘Mycogen 8N 429 CL’, ‘Pioneer 01 RL 0004’, ‘Pioneer 03 BM 0024’.

Additional index words: Crop injury, crop rotation interval, herbicide injury, plant-back restriction.

Abbreviations: WAE, weeks after emergence.

Soil-residual herbicides can be applied to the soil under grapevines during fall or spring before weed emergence. But, early spring moisture and warm weather conditions may enhance weed emergence before spring herbicide applications. Therefore, fall application of herbicide can be useful if the herbicides provide adequate weed control the following spring and summer. Fall and spring applications of oryzalin or norflurazon, applied alone or in combination with diuron, simazine, or oxyfluorfen, were evaluated for weed control in grape at Oskaloosa and Eudora in northeast Kansas in the 2002 to 2003 and 2003 to 2004 growing seasons. Weeds were not controlled adequately with oryzalin or norflurazon applied alone. At the end of the growing season, weed control was 10 to 20% greater when herbicides were applied in the spring than when applied in the fall. In addition, weed control with norflurazon was slightly greater than with oryzalin. In general, norflurazon or oryzalin applied in combination with simazine, diuron, or oxyfluorfen gave greater weed control than norflurazon or oryzalin applied alone. The greatest control was with norflurazon or oryzalin applied with oxyfluorfen. In general, all herbicide combinations provided similar weed control 4 mo after spring treatment in 2003 and 3 mo after spring treatment in 2004. This study showed that acceptable weed control can be achieved when norflurazon or oryzalin is applied with oxyfluorfen or diuron in the fall.

Nomenclature: Diuron; norflurazon; oryzalin; oxyfluorfen; simazine; grape, Vitis labrusca #³ VITLA.

Additional index words: Grape injury, common ragweed, horseweed, prickly sida, prickly lettuce, tumble windmillgrass, yellow sweetclover.

Abbreviations: MAST, month after spring treatment.

Experiments were conducted in weed-free environments to determine corn tolerance to trifloxysulfuron applied PRE or POST, and to determine the potential for trifloxysulfuron applied PRE or POST to cotton to injure corn grown in rotation the following year. Trifloxysulfuron at 3.75, 7.5, or 15 g ai/ha applied PRE or POST resulted in 98% stand reduction of imidazolinone-tolerant (IT) corn and 100% stand reduction in conventional corn. No injury occurred to imidazolinone-resistant (IR) corn. A corn cultivar yield response was observed, with conventional nontreated corn yielding 8,850 kg/ha and greater than nontreated IT corn at 7,900 kg/ha. Nontreated IR corn yielded the least, at 6,400 kg/ha, and these yields were equivalent to trifloxysulfuron-treated IR corn at 6,590 kg/ha. Cotton treated with trifloxysulfuron PRE at any rate was injured less than 8%. Both trifloxysulfuron at 7.5 g/ha POST and pyrithiobac at 70 g ai/ha POST injured cotton 11% early in the season. Neither trifloxysulfuron nor pyrithiobac influenced weed-free cotton lint yields. When grown in rotation, corn was not injured by trifloxysulfuron or pyrithiobac applied the previous year to cotton, and yields were not influenced.

Nomenclature: Trifloxysulfuron; cotton, Gossypium hirsutum L.; corn, Zea mays L.

Additional index words: Carryover, crop injury, sulfonylurea herbicide.

Abbreviations: ALS, acetolactate synthase.

Glyphosate-resistant corn was no-till planted into alfalfa that was in the early bud stage (UNCUT) or had been cut 3 to 4 d earlier and baled for hay (CUT). Alfalfa control and corn yield were measured in nontreated plots as well as plots treated with glyphosate alone or tank-mixed with 2,4-D or dicamba applied at planting (AP) or POST. Alfalfa control was greater for all AP treatments of UNCUT compared to CUT alfalfa. Glyphosate plus dicamba applied AP controlled alfalfa better than the other AP treatments resulting in increased corn yield compared with other AP treatments. Postemergence applications of glyphosate alone or tank-mixed with 2,4-D or dicamba controlled alfalfa better 6 weeks after treatment than AP applications of the same herbicides; however, corn yield for AP treatments were similar or greater than the yield of POST applications of the same herbicides. Corn yield averaged 13% higher following herbicide applications to UNCUT compared with CUT alfalfa, so the value of alfalfa hay must be weighed against the loss of corn yield when making decisions concerning the management of an alfalfa–corn rotation.

Nomenclature: 2,4-D dimethylamine salt; dicamba; glyphosate; alfalfa, Medicago sativa L. #³ MEDSA; corn, Zea mays L. # ZEAMX.

Additional index words: Perennial weed control.

Abbreviations: WAT, weeks after treatment.

Giant smutgrass is a perennial, clump-type, grassy weed that commonly infests Florida pastures. Experiments were conducted in 1998 and 1999 in Immokalee, FL, to evaluate multiple mowing treatments in combination with hexazinone applications at 0.56 to 1.7 kg ai/ha, to control giant smutgrass and bahiagrass density. Mowing did not influence giant smutgrass control in 1998 or 1999. Hexazinone application increased giant smutgrass control at all application rates. In 1998, regression analysis determined that hexazinone applied at 0.56 kg/ha provided >90% control of giant smutgrass 182 d after treatment (DAT) and >80% control 321 DAT. Both 1.1 and 1.7 kg/ha of hexazinone provided >90% control for 365 DAT in 1998. In 1999, due in part to excessive rainfall, 0.56 kg/ha provided >80% control for only 48 DAT. It was also concluded that application rates of 0.83 to 0.98 kg/ha hexazinone were the lowest rates that consistently provided 80% or better control over both years. From 0 to 30 DAT, bahiagrass density increased by 17% for the 0.56 kg/ha rate and 2% at the 1.7 kg/ha rate. From 30 to 365 DAT, bahiagrass density increased at 0.04% per day compared with 0.1% per day for 0.56 and 1.7 kg/ha, respectively. Increased bahiagrass injury by the higher application rates of hexazinone was responsible for low levels of bahiagrass growth from 0 to 30 DAT. However, bahiagrass soon recovered from injury, and the higher application rates resulted in a more rapid rate of bahiagrass spread, likely due to less competition of giant smutgrass in plots treated with 1.1 and 1.7 kg/ha rates. These data prove that mowing prior to hexazinone application is an unwarranted expense, and that the 1.1 kg/ha rate provided the most effective and consistent giant smutgrass control with acceptable levels of bahiagrass injury.

Nomenclature: Hexazinone; giant smutgrass, Sporobolus indicus (L.) R. Br. var. pyramidalis (P. Beauv.) Veldkamp; bahiagrass, Paspalum notatum Fluegee, #³PASNO.

Additional index words: Bahiagrass density, hexazinone, pasture weeds, tropical forage.

Several new herbicides have been registered for pasture weed control, but their effect on ‘Coastal’ bermudagrass dry matter (DM) yield has not been documented. The objective of this study was to determine the effect of clopyralid, fluroxypyr, imazapic, picloram, picloram fluroxypyr, picloram 2,4-D amine, triasulfuron dicamba, triclopyr amine clopyralid, triclopyr ester, triclopyr ester fluroxypyr, trifloxysulfuron, 2,4-D amine dicamba, and 2,4-D ester on Coastal bermudagrass yield. Total DM yields of Coastal bermudagrass were not reduced by 0.84 kg/ha clopyralid, 0.031 kg ai/ha triasulfuron 0.44 kg ai/ha dicamba, 1.205 kg ai/kg 2,4-D amine 0.42 kg/ha dicamba, and 2.31 kg/ha 2,4-D ester. Although 0.227 kg ai/ha picloram 0.84 kg/ha 2,4-D amine, 0.945 kg ai/ha triclopyr amine 0.315 kg ai/ha clopyralid, and 1.68 kg ai/ha triclopyr ester reduced Coastal bermudagrass DM yields in harvest 1, there was no cumulative loss in total production in either 2001 or 2002 with these herbicides compared with that of the nontreated control. Coastal bermudagrass total DM yields were reduced by 52% with 0.158 kg ai/ha imazapic when applied to dormant bermudagrass in 2001, and by 26% with 0.021 kg ai/ha trifloxysulfuron when applied to actively growing bermudagrass in 2001; however, neither herbicide reduced total cumulative yield in 2002. In 2001 and 2002, total DM yield was reduced by an average of 25% with 0.42 kg/ha fluroxypyr, by 45% with 0.105 kg/ha imazapic, by 57% with 0.158 kg/ha imazapic, by 65% with 0.21 kg/ha imazapic, by 25% with 0.56 kg/ha picloram, by 20% with 0.188 kg/ha picloram 0.188 kg/ha fluroxypyr, and by 18% with 0.63 kg/ha triclopyr ester 0.21 kg/ha fluroxypyr, when applied to actively growing Coastal bermudagrass.

Nomenclature: Clopyralid; dicamba; fluroxypyr; imazapic; picloram; triasulfuron; triclopyr amine; triclopyr ester; trifloxysulfuron; 2,4-D amine; 2,4-D ester; bermudagrass, Cynodon dactylon (L) Pers. ‘Coastal’ #³ CYNDA.

Additional index words: Bermudagrass tolerance, injury, yield.

Field experiments were conducted in 2001 through 2003 in Wooster, OH, to determine strawberry (Fragaria X ananassa) plant response to clopyralid applied after plant renovation in established plantings. Clopyralid applied at a rate of 200 g ae/ha or greater controlled at least 82% of common groundsel (Senecio vulgaris) 6 wk after treatment (WAT). Maximum total fruit yield (marketable plus unmarketable fruits) occurred at a clopyralid rate of 200 g/ha, and higher or lower rates resulted in reduced yield. Application of clopyralid at 400 g/ha tended to reduce the canopy of the strawberry crop, especially in comparison to rates lower that 200 g/ha. Overall, clopyralid applied POST at 200 g/ha did not reduce fruit yield when applied after strawberry renovation, and effectively controlled common groundsel plants that were entering the reproductive stage.

Nomenclature: Clopyralid; common groundsel, Senecio vulgaris L. #³ SENVU; strawberry, Fragaria X ananassa Duch.

Additional index words: Herbicide tolerance, postrenovation application.

Protoporphyrinogen oxidase (protox)-inhibiting herbicides damage cell membranes, resulting in electrolyte leakage. A whole-plant dose-response study and a rapid assay that measured electrolyte leakage was used to determine the response of wild mustard, soybean, and protox inhibitor–susceptible and protox inhibitor–resistant common waterhemp to increasing doses of three protox inhibitors: acifluorfen, fomesafen, and sulfentrazone. For the dose-response study, whole plants were treated with the three protox-inhibitor herbicides. Electroconductivity assay 1 consisted of cutting discs from leaf tissue and submerging them in an incubation medium containing concentrations of acifluorfen, fomesafen, or sulfentrazone. In electroconductivity assay 2, the entire leaf was treated with solutions containing acifluorfen, fomesafen, or sulfentrazone. The whole-plant dose-response study showed increasing visible injury with increasing herbicide rates for all species and all herbicides. The order of visible injury was wild mustard > susceptible common waterhemp > resistant common waterhemp > soybean. In assay 1, electrolyte leakage from leaf discs treated with acifluorfen or fomesafen increased with increasing herbicide concentrations, and was similar for all species. In contrast, electrolyte leakage from leaf discs treated with sulfentrazone did not increase with increasing herbicide concentrations for any species. In assay 2, only wild mustard leaf discs increased in electrolyte leakage with increasing herbicide rates of acifluorfen, fomesafen, and sulfentrazone and followed the regression curves established by the whole-plant dose-response study. However, assay 2 was not able to distinguish between susceptible wild mustard and tolerant soybean, or between susceptible and resistant waterhemp.

Nomenclature: Acifluorfen; fomesafen; sulfentrazone; common waterhemp, Amaranthus rudis Sauer, #³ AMATA; wild mustard, Brassica kaber (DC.) L.C. Wheeler, # SINAR; corn, Zea mays L.; soybean, Glycine max (L.) Merr. ‘Asgrow 3302’; sunflower, Helianthus annuus L.

Additional index words: Electrolyte leakage, herbicide application, herbicide resistance.

Abbreviations: DAT, days after treatment; proto, protoporphryin IX; protogen, protoporphyrinogen IX; protox, protoporphyrinogen oxidase [E.C. 1.3.3.4].

Field research was conducted for 2 yr to evaluate response of corn and rice to simulated drift rates of a commercial premix of imazethapyr plus imazapyr [3:1 (w/w)]. Drift rates of the imazethapyr plus imazapyr premix represented 0.8, 1.6, 3.2, 6.3, and 12.5% of the usage rate of 63 g ai/ha (0.5, 1, 2, 4, and 7.9 g/ha, respectively). The imazethapyr plus imazapyr premix applied to six-leaf corn at 7.9 g/ha reduced height 11% compared with the nontreated control 7 days after treatment (DAT) but did not affect corn height 14 and 28 DAT. Corn yield was equivalent regardless of imazethapyr plus imazapyr rate and ranged from 10,200 to 11,500 kg/ha. At 28 DAT, rice height was reduced 12% when 7.9 g/ha of the imazethapyr plus imazapyr premix was applied early postemergence (EPOST) at two- to three-leaf and 14 and 5% when the imazethapyr plus imazapyr premix at 7.9 and 4 g/ha, respectively, was applied late postemergence (LPOST) at panicle differentiation. Reductions in mature rice height of 11 and 6% were observed when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, and a 5% reduction was observed for 7.9 g/ha of the imazethapyr plus imazapyr premix applied EPOST. Application of the imazethapyr plus imazapyr premix EPOST at 7.9 g/ha delayed heading in only 1 yr, but heading was delayed both years when applied LPOST. Rice yield was reduced 39 and 16% when the imazethapyr plus imazapyr premix was applied LPOST at 7.9 and 4 g/ha, respectively, compared with a 9% yield reduction for 7.9 g/ha applied EPOST.

Nomenclature: Imazapyr; imazethapyr; corn, Zea mays L. ‘Dekalb 687’; rice, Oryza sativa L. ‘Cypress’.

Additional index words: Crop injury, herbicide drift, off-target movement.

Abbreviations: IR, imidazolinone-resistant.

Tolerance of eight market classes of dry beans (black, brown, cranberry, kidney, otebo, pinto, white, and yellow eye beans) to the PRE application of linuron at the rate of 2.25 and 4.50 kg ai/ha was studied at two locations in Ontario, Canada, in 2003 and 2004. The eight market classes differed in their response to linuron. Linuron PRE caused as much as 43, 20, 7, 17, 54, 36, 56, and 12% visual injury in black, brown, cranberry, kidney, otebo, pinto, white, and yellow eye beans, respectively. Linuron PRE at 2.25 kg/ha reduced plant height 38% in otebo beans and 31% in white beans. Linuron PRE at 4.50 kg/ha reduced plant height 24 to 56% in black, brown, otebo, pinto, and white beans. Shoot dry weight was reduced in otebo beans by 56% and in white beans, by 46% at the low rate. Shoot dry weight was decreased 26 to 92% in black, otebo, pinto, white, and yellow eye beans at the high rate. There were no differences in the shoot dry weight of the other market classes. Linuron PRE at the low rate reduced otebo bean yield 42% and at the high rate reduced yields by 56, 74, and 61% in black, otebo, and white beans, respectively. There was no effect on the yield of other market classes. Differences in dry bean market class tolerance to linuron exists and may be summarized for these cultivars as cranberry > kidney > brown > yellow eye > pinto > black > white > otebo. Additional research is needed to determine if cultivars within a dry bean market class differ in their response to linuron.

Nomenclature: Linuron; Black bean, ‘AC Harblack’; otebo bean, ‘Hime’; pinto bean, ‘GTS 900’; white bean, ‘OAC Thunder’; brown bean, ‘Berna’; cranberry bean, ‘Hooter’; kidney bean, ‘Montcalm’; yellow eye bean, ‘GTS 1701’; Phaseolus vulgaris L. #³ PHSVX.

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

Abbreviations: DAE, days after emergence; OM, organic matter.

Annual bluegrass and roughstalk bluegrass are turfgrasses, but they can also be two of the most serious weed problems in highly maintained turfgrass. Ethofumesate has been used to control annual bluegrass; however, the results have been erratic, and ethofumesate is not widely utilized for annual bluegrass control in turfgrass. The objective of this research was to characterize the response of annual, roughstalk, and Kentucky bluegrasses and creeping bentgrass to a range of ethofumesate rates. Single applications of ethofumesate from 3.4 to 20.2 kg ai/ha were made to all four species during May of 1999 to 2001. All four species were injured from rates of ≥6.7 kg/ha. Roughstalk bluegrass was most injured by a single ethofumesate application. Percent roughstalk bluegrass control increased linearly with rate, and greater than 85% control was observed for rates of ≥16.8 kg/ha. In contrast, annual bluegrass showed almost no control, with rates ≤10.2 kg/ha, and the highest rate tested, 20.2 kg/ha, controlled only 47 to 62% of the annual bluegrass. Kentucky bluegrass was the least sensitive bluegrass species, with a maximum control of 3 to 15% from 20.2 kg/ha of ethofumesate. Creeping bentgrass was the least sensitive of the species tested, with low levels of control regardless of rate. During 3 yr of testing, maximum control of bentgrass from any rate was 4%. Single, high-rate applications of ethofumesate hold promise to control roughstalk bluegrass in creeping bentgrass turf. Sixteen Kentucky bluegrass cultivars used for low-cut athletic fields were evaluated for their tolerance to sequential ethofumesate applications during 1999 and 2002. The cultivars showed significant differences in ethofumesate tolerance, with ‘Moonlight’ and ‘America’ never showing any injury to sequential ethofumesate applications, while ‘Northstar’ and ‘Total Eclipse’ were severely injured.

Nomenclature: Ethofumesate, annual bluegrass, Poa annua L. #³ POAAN; roughstalk bluegrass, Poa trivialis L. #POATR ‘Laser’; Kentucky bluegrass, Poa pratensis L. #POAPR ‘Northstar,’ ‘Total Eclipse,’ ‘Limosine,’ ‘Explorer,’ ‘ZPS 309,’ ‘Rambo,’ ‘Rugby II,’ ‘SR2000,’ ‘Ram1,’ ‘Wildwood,’ ‘Odyssey,’ ‘Absolute,’ ‘SR 2109,’ ‘America,’ ‘Moonlight,’ ‘Gnome,’ ‘Glade,’ ‘Nustar,’ and ‘Baron’; creeping bentgrass, Agrostis stolonifera L. #AGSST ‘Penneagle,’ ‘SR 1020,’ ‘SR 1019,’ and ‘Providence,’

Additional index words: Field study, tolerance, postemergence grass control.

Abbreviation: WAT, weeks after treatment.

Studies were conducted in 1999, 2000, and 2001 to evaluate broadleaf weed control in cotton from POST applications of trifloxysulfuron plus pyrithiobac. Trifloxysulfuron was applied at 2.5, 5, and 7.5 g ai/ha, and pyrithiobac was applied at 0, 17, and 35 g ai/ha in a factorial treatment arrangement. Cotton injury was affected by rates of both herbicides at 7 and 14 d after treatment (DAT) with injury ranging from 19 to 26%. Broadleaf weed control at 28 DAT from mixtures of the herbicides was generally commercially acceptable. Combinations of 17 or 35 g/ha pyrithiobac plus trifloxysulfuron controlled common ragweed, velvetleaf, common lambsquarters, annual morningglory species (ivyleaf morningglory, pitted morningglory, and tall morningglory), common cocklebur, spurred anoda, and jimsonweed at least 73% at 28 DAT. Trifloxysulfuron applied alone failed to control velvetleaf, spurred anoda, and jimsonweed. Cotton yield reflected weed control and yields increased with pyrithiobac rates. It is concluded that the spectra of the weeds controlled by trifloxysulfuron and pyrithiobac were highly complementary in these studies.

Nomenclature: Trifloxysulfuron; pyrithiobac; annual morningglory species, Ipomoea spp.; common cocklebur, Xanthium strumarium L. #³ XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L # AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; pitted morningglory, Ipomoea lacunosa L. # IPOLA; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; tall morningglory, Ipomoea purpurea (L.) Roth # PHBPU; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L.

Additional index words: Acetolactate synthase (ALS), herbicide mixtures.

Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); POSD, postdirected.

Greenhouse and laboratory experiments were conducted to investigate the response of common lambsquarters to POST applications of halosulfuron–methyl plus 2,4-D admixtures and to investigate the effects of 2,4-D on the absorption, translocation, and metabolism of halosulfuron. In the greenhouse, halosulfuron at 0, 4.5, 9, 18, and 36 g ai/ha was applied alone and mixed with 2,4-D at 0, 17, 35, and 70 g ai/ha POST to 7.5- to 9-cm seedlings, and plant fresh weights were determined 4 wk after treatment (WAT). Halosulfuron alone did not control this weed, while fresh weights of common lambsquarters treated with 2,4-D declined hyperbolically as rates increased. A synergistic response for mixtures of these herbicides occurred, as observed fresh weights for all combinations were less than expected based on independent action and the calibrated marginal responses. In the laboratory, 7.5- to 9-cm seedlings were treated POST with commercially formulated halosulfuron at 9 and 18 g/ha and 2,4-D at 0, 70, and 140 g/ha, respectively, followed by foliar-applied ¹⁴C-halosulfuron. Absorption of ¹⁴C-halosulfuron increased with time, and absorption and translocation were not influenced by the addition of 2,4-D. Results from these studies inferred that halosulfuron and 2,4-D were generally synergistic on common lambsquarters and that mechanisms other than absorption, translocation, and metabolism may explain this response.

Nomenclature: 2,4-D; halosulfuron; common lambsquarters, Chenopodium album L.#³ CHEAL.

Additional Index Words: Absorption, synergism, translocation, metabolism, herbicide mixtures, acetolactate synthase.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); CDE, combined dosage equivalency; HAT, hours after treatment; LSS, liquid scintillation spectroscopy; NIS, nonionic surfactant; TLC, thin-layer chromatography.

Research was conducted to determine the minimum number of between-row mowings necessary to control annual weeds, chiefly giant foxtail and common waterhemp, without corn yield loss. Over 2 yr in Missouri, the between-row mowing systems that were evaluated consisted of a 38-cm band of PRE atrazine plus metolachlor at 2.2 plus 2.2 kg ai/ha applied over corn grown in 76-cm rows shortly after planting followed by one, two, or three between-row mowings close to the soil surface. Based on rated total weed control, between-row total weed cover, and corn yield, the weed-free check was statistically indistinguishable from a treatment in which banded PRE herbicide was followed by only one between-row mowing, late, when weeds were relatively large. When mowed once at 52 to 64 days after planting (DAP), giant foxtail and common waterhemp were greater than 85 cm tall. The yield was not increased by mowing earlier or more than once.

Nomenclature: Atrazine; metolachlor; giant foxtail, Setaria faberii (L.) Beauv. #^3, SETFA; common waterhemp, Amaranthus rudis Sauer. #³ AMATA; corn, Zea mays L. ‘Pioneer 3379’ #ZEAMX.

Additional index words: Alternative weed control, banding, banded application, cutting, mechanical weed control, nonchemical weed control, reduced rate herbicide.

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

The “micro-rate” application, a POST combination of desmedipham plus phenmedipham at 0.045 0.045 kg ai/ha (desphen) or desmedipham plus phenmedipham plus ethofumesate³ (1:1: 1 ratio) (desphenetho) at 0.09 kg ai/ha plus triflusulfuron at 0.004 kg ai/ha plus clopyralid at 0.026 kg ae/ha plus 1.5% methylated seed oil received registration in 1998 and 2000 in North Dakota and Michigan, respectively. Herbicide rates are reduced by 80%, compared to standard-split applications, and growers typically apply the micro-rate three to five times to very small weeds that are 1 cm or less in height. In standard-split applications, growers make two sequential applications, the first when weeds are 1.5 cm tall and the sequential application usually 10 to 14 d later. Research was conducted in small plots and large grower plots in 2001 and 2002 to determine the effect of PRE herbicides on weed control and sugarbeet injury from micro-rates compared to standard-split POST herbicide applications. Sugarbeet populations were reduced in the cycloate treatment compared to all other PRE and the no-PRE treatment in 2001 and in the S-metolachlor compared to the ethofumesate treatment in 2002. Sugarbeet injury was 6% or less from POST-only treatments in 2001. Control of common lambsquarters and Amaranthus spp. by desphen and desphenetho treatments was similar. Sugarbeet injury in 2002 was 29 to 43% from POST-only treatments. The standard-split of desphenetho was more injurious than the standard-split of desphen. Common lambsquarters control was greater in both the standard-split and micro-rate of desphenetho compared to the standard-split of desphen in 2002. However, sugarbeet populations and recoverable white sucrose per hectare did not differ among POST herbicide treatments in either year. No herbicide program provided 100% control of all weeds in both years. In the seven large production fields, PRE herbicide treatments did not reduce sugarbeet populations or recoverable sucrose per hectare compared to the no-PRE control. Weed control from four POST micro-rate applications only was similar to weed control in instances in which PRE herbicides were applied prior to the POST micro-rate applications.

Nomenclature: Cycloate, pyrazon, ethofumesate, desmedipham plus phenmedipham, triflusulfuron, clopyralid, Chenopodium album L. #⁴ CHEAL; Amaranthus species # AMASS.

Additional index words: Micro-rate, standard-split.

Abbreviations: DAT, days after treatment; desphen, desmedipham phenmedipham; desphenetho, desmedipham phenmedipham ethofumesate; fb, followed by; RWSH, recoverable white sucrose per hectare.

Trials were conducted under weed-free conditions in 2001, 2002, and 2003 on a loamy sand soil in Georgia to investigate the phytotoxicity of flumioxazin on peanut, and in separate trials, the effects on peanut maturity. The first study evaluated time of flumioxazin application (0, 2, 4, 6, 8, and 10 d after planting [DAP]) and flumioxazin rate (nontreated, 71, and 105 g ai/ha). Peanut (variety ‘C99R’) were seeded 3.2 cm deep and irrigated immediately after seeding. Flumioxazin applied to peanut 6, 8, and 10 DAP significantly injured peanut (20 to 59%) early season, with more phytotoxicity from flumioxazin at 105 g/ha than 71 g/ha. However, peanut stand was not reduced by any of the times of application or rates. Peanut recovered by midseason, except in cases of severe (up to 49%) visual phytotoxic injury. Peanut yields were not affected by either flumioxazin application timing or rate. The second study (variety ‘Georgia Green’) evaluated flumioxazin applied at 105 g/ha at varying intervals after planting to determine the phytotoxic effects on peanut maturity using the hull-scrape method. Peanut maturity was delayed by flumioxazin when applied 1 d after planting and later. These results show that the optimum time of application is from immediately after planting to 2 d after planting, but ideally, the application should be made immediately after planting. The highest recommended flumioxazin rate, 105 g/ha, is not significantly phytotoxic when applied within the recommended range of timings and has no effect on yield. However, there is potential for yield loss as peanut maturity is delayed in cases of severe injury.

Nomenclature: Peanut, Arachis hypogaea L.; flumioxazin.

Additional index words: Hull-scrape method, peanut injury, peanut maturity.

Abbreviations: DAE, days after emergence.

Greenhouse and field experiments were conducted near Knoxville, TN, during 2002 and 2003 to investigate the effects of calcium and magnesium ions on the performance of three glyphosate formulations with and without diammonium sulfate (AMS). Weed species investigated in the greenhouse were broadleaf signalgrass, pitted morningglory, Palmer amaranth, and yellow nutsedge. Three glyphosate formulations (isopropylamine salt, diammonium salt, and potassium salt) and two glyphosate application rates (0.42 and 0.84 kg ae/ha) were applied to weeds in water fortified with either calcium or magnesium at concentrations of 0, 250, 500, 750, and 1,000 ppm. In all comparisons, there were no differences in the three glyphosate formulations. Glyphosate activity was reduced only when cation concentration was >250 ppm, and this antagonism was not observed when 2% w/ w AMS was added to the spray solution. A chemical analysis of the calcium and magnesium concentrations in water collected from farmers indicated that water samples from eight different producers contained relatively low amounts of cations, with calcium at <40 ppm and magnesium at <8 ppm. In the field results using these and other waters as the herbicide carrier, broadleaf signalgrass control was greater with the 0.84 kg ae/ha than 0.42 kg ae/ha glyphosate rate regardless of water source or addition of AMS. Pitted morningglory responded similarly to glyphosate with water from all farms and with AMS added, and the addition of AMS gave similar results for both glyphosate rates. In 2003, common cocklebur was evaluated and control was >93% regardless of glyphosate rate, water source, or AMS addition. Based on these results, the addition of AMS-based adjuvants to many glyphosate applications may not be warranted.

Nomenclature: Glyphosate; diammonium sulfate; broadleaf signalgrass, Brachiaria platyphylla L. #³ BRAPP; Palmer amaranth, Amaranthus palmeri L. # AMAPA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; yellow nutsedge, Cyperus esculentus L. # CYPES; soybean, [Glycine Max (L). Merr. var ‘Asgrow 5602’].

Additional index words: Antagonism, hard water.

Abbreviations: DAT, days after treatment; ICAP, inductively coupled argon plasma.

Herbicide-resistant corn hybrids offer additional options for POST weed control in corn, and growers may benefit from information on the consistency of these weed-control strategies. Studies were conducted in Indiana, Illinois, Michigan, and Ohio, in 2000 and 2001, to evaluate weed control among herbicide strategies for imidazolinone-resistant, glufosinate-resistant, glyphosate-resistant, and conventional corn. Isogenic hybrids were utilized to minimize variation in growth and yield potential among hybrids. The glyphosate-resistant corn postemergence (glyphosate-POST) treatment provided more consistent control of giant foxtail than the PRE, conventional corn postemergence (conventional-POST), glufosinate-resistant corn postemergence (glufosinate-POST), and imidazolinone-resistant corn postemergence (imi-POST) treatments. All four POST treatments were more consistent and provided greater control than the PRE treatment of the large-seeded broadleaf weeds velvetleaf, giant ragweed, common cocklebur, and morningglory species. Conventional-POST and imi-POST were more consistent than glufosinate-POST and glyphosate-POST treatments in controlling giant ragweed. There were no statistical differences in the variability of PRE or POST treatments for control of common lambsquarters, common ragweed, and redroot pigweed. Corn yield varied among locations and years. The glyphosate-POST treatment did not reduce yield relative to the weed-free treatment, the imi-POST and glufosinate-POST treatments each reduced yield in one of eight locations, and the conventional-POST treatment reduced yield in three of eight locations.

Nomenclature: Metolachlor; atrazine; nicosulfuron; rimsulfuron; dicamba; imazethapyr; imazapyr; glufosinate; glyphosate; common cocklebur, Xanthium strumarium L. #³ XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi (L.) Herrm. # SETFA; giant ragweed, Ambrosia trifida L. # AMBTR; morningglory species, Ipomea spp. # IPOSS; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; corn, Zea mays L. # ZEAMX.

Additional index words: Corn yield, herbicide-resistant crop, herbicide system, Ipomea species, conventional corn, imidazolinone.

Abbreviations: AMS, ammonium sulfate; crm, comparative relative maturity; DAP, days after postemergence.

Greenhouse studies were conducted to determine the effect of 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS) as a spray adjuvant on the efficacy of three different glyphosate formulations, the isopropylamine salt (glyphosate-IPA), potassium salt (glyphosate-K), and the acid of glyphosate dissolved in AMADS (glyphosate-A). All formulations were tested at multiple rates with and without AMADS (2% v/v) on greenhouse-grown corn, and growth inhibition was determined by measuring the elongation of the newest emerging leaf between 1 and 7 d after treatment. AMADS increased the efficacy of all three glyphosate formulations by threefold to fourfold. The IC₅₀ values for glyphosate-IPA, glyphosate-K, and glyphosate-A without AMADS on corn were 77, 54, and 53 g ae/ha, respectively; and with AMADS the values were 20, 18, and 21 g/ha, respectively. AMADS was more effective than ammonium sulfate (2% w/v) in overcoming the antagonism of hard water (200 parts per million Ca ²) on glyphosate-K efficacy on corn. The rainfastness of glyphosate-IPA, glyphosate-A, and glyphosate-K was improved with AMADS.

Nomenclature: Glyphosate; corn, Zea mays L. ‘Triumph 1416’.

Additional index words: Ammonium sulfate, rainfastness, surfactant.

Abbreviations: AMS, ammonium sulfate; DAT, days after treatment; glyphosate-TMS, formulated trimethylsulfonium salt of glyphosate; HAT, hours after treatment; IC₅₀, concentration that inhibits growth by 50%; NIS, nonionic surfactant.

There is a high potential for inadvertent herbicide injury to crops in western Canada on an annual basis because of the diversity of crops grown in close proximity to each other, although accurate data regarding the annual number of injury incidents is not available. A field study was conducted at two locations in southern Manitoba, Canada, in 2001 and 2002, to investigate the effects of a range of dosages of MCPA ester, glyphosate, and thifensulfuron:tribenuron (2:1) applied to the seedling growth stage of conventional (nongenetically engineered) canola and white bean on subsequent shoot dry matter and crop yield. Similar to other studies that utilized sublethal herbicide dosages, results between site-years were variable, particularly for crop yield. Where possible, a nonlinear log-logistic model was fitted to the data. Generally, canola was more sensitive than white bean to the herbicides used in this study. Based on the fitted regression equations and recorded mean values for canola, 10% of the commercial herbicide dosage normally applied in other (possibly adjacent) crops caused greater than 10% canola yield loss for 9 of 12 unique combinations of herbicide-site-year. For white bean, 10% of the commercial herbicide dosage caused yield losses greater than 10% for only 4 of 13 unique combinations of herbicide-site-year. Spray drift is probably the most common source of inadvertent application of herbicide to sensitive crops; generally, only a fraction of the herbicide dosage applied on an adjacent crop drifts off-target. The results of this study indicate that for any of the three herbicides investigated on canola and white bean, it is difficult to accurately predict eventual crop yield loss based on early season sublethal herbicide injury symptoms due to site-year variability and the potential for crop recovery and compensatory growth. This response was particularly true for white bean in this study.

Nomenclature: Glyphosate, isopropylamine salt; MCPA, iso-octyl ester; thifensulfuron, methyl ester; tribenuron, methyl ester; canola, Brassica napus L. ‘46A65’; white bean, Phaseolus vulgaris L. ‘Envoy’.

Additional index words: Herbicide drift, herbicide injury, sublethal dosage, dose response.

A 3-yr dryland study was initiated in 1999 at Munday, TX, on an Altus fine sandy loam to determine the most appropriate cotton growth stage or stages at which to apply glyphosate. The objectives were: (1) to evaluate control of silverleaf nightshade in the cotton and (2) to determine the effect on yield. Treatments were: (1) control (C; two cultivations), (2) early glyphosate at the four-leaf stage (E), (3) early glyphosate followed by a midseason application 21 d later (E M), (4) two cultivations plus late glyphosate at 20% open bolls (L), (5) treatment E L, and (6) treatment E M L. In fall 1999 and 2001, silverleaf nightshade stem numbers decreased in the plots sprayed early and midseason, and increased in plots receiving only late or no applications when compared with the counts in the spring of those years. However, in fall 2000, nightshade numbers were less than in early spring 2000 regardless of treatment, probably because of hot and dry weather. In fall 2001, silverleaf nightshade populations had increased 13-fold and twofold for the C and L treatments, respectively, when compared with populations at the beginning of the study. Other treatments had population decreases of 10 to 90%. Three-year average lint yields were higher with early or early plus midseason applications. Lint yields were similar with early or early plus midseason sprays. Lint yields were higher when nightshade/cotton biomass competition was lower. Early application of glyphosate can effectively control silverleaf nightshade populations and can increase yield when compared to no application or a late application.

Nomenclature: Glyphosate; trifluralin; silverleaf nightshade, Solanum elaeagnifolium Cav.; glyphosate-resistant cotton, Gossypium hirsutum L.

Additional index words: Silverleaf nightshade, glyphosate, glyphosate-resistant cotton, lint yield, weed control.

The effects of spring tillage sequence on summer annual weed populations were evaluated over two cycles of a 3-yr crop rotation of snap beans, sweet corn, and winter wheat. Continuous no-till (N) planting of vegetable crops each spring (NNNN) reduced summer annual weed density 63 to 86% compared to that of continuous conventional tillage (CCCC), depending upon site and herbicide level. Hairy nightshade populations were reduced by 88 to 96% when spring tillage was eliminated from the crop rotation. The effects of the NNNN spring tillage sequence on weed density were similar at two sites even though the crop rotations at the two sites began with different crops. The rotational tillage sequence of NCNC at the East site, in a crop rotation that began with corn, reduced summer annual weed density by 46 to 51% compared to that of continuous conventional tillage and planting (CCCC) at low and medium herbicide rates, respectively. In contrast, the tillage sequence of CNCN in the same crop rotation and at the same site increased weed density by 80% compared to that of CCCC at a low herbicide rate. The effects of the NCNC and CNCN rotational tillage sequences on weed density were reversed at the West site, and was probably caused by pairing sweet corn with conventional tillage rather than no tillage. The reduction in summer annual weed density caused by reduced spring tillage frequency did not significantly increase crop yields.

Nomenclature: Glyphosate; lactofen; metolachlor; barnyardgrass, Echinochloa crus-galli L. Beauv ECHCG; common lambsquarters, Chenopodium album L. CHEAL; hairy nightshade, Solanum sarrachoides Sendtner SOLSA; Powell amaranth, Amaranthus powellii S. Wats AMAPO; redroot pigweed, Amaranthus retroflexus L.; smooth pigweed, Amaranthus hybridus L.; snap beans, Phaseolus vulgaris L. ‘OR91G’; spring barley, Hordeum vulgare L. ‘Micah’; sweet corn Zea mays L. ‘Golden Jubilee’.

Additional index words: Conventional tillage, crop rotation, direct-seeding, no-till, rotational tillage, seedbank, seedling recruitment, weed density.

Abbreviations: H, high; HL, herbicide level; L, low; M, medium; TS, tillage sequence; WAP, weeks after planting.

Three field experiments were conducted to evaluate efficacy of BAS 625, cyhalofop, and fenoxaprop plus isoxadifen when applied alone or with acifluorfen plus bentazon, acifluorfen, bentazon, triclopyr, bensulfuron, halosulfuron, carfentrazone, and propanil. Broadleaf signalgrass control with fenoxaprop plus isoxadifen was reduced by triclopyr and halosufuron. None of these herbicides reduced Amazon sprangletop control by fenoxaprop plus isoxadifen. Barnyardgrass control with fenoxaprop plus isoxadifen was reduced by halosulfuron and propanil. Barnyardgrass and Amazon sprangletop control by cyhalofop was reduced by bentazon plus acifluorfen, bentazon, acifluorfen, triclopyr, bensulfuron, or halosulfuron. Broadleaf signalgrass control with cyhalofop was reduced by triclopyr and halosulfuron. Amazon sprangletop control by cyhalofop was reduced by all herbicides. Barnyardgrass control with BAS 625 was reduced when applied with propanil, bentazon, or bentazon plus acifluorfen. Broadleaf signalgrass control with BAS 625 was reduced when applied with bentazon plus acifluorfen. Amazon sprangletop control with BAS 625 was reduced when applied with bentazon, acifluorfen, halosulfuron, or propanil.

Nomenclature: BAS 625, 2-[1-[2-(4-chlorophenoxy)propoxyimino]-butyl]3-oxo-5-thian-3-ylcyclohex-1-enol; acifluorfen; bensulfuron; bentazon; carfentrazone; cyhalofop; fenoxaprop; halosulfuron; isoxadifen (4,5-dihydro-5,5-diphenyl-3-isoxazolecarboxylic acid); propanil; triclopyr; Amazon sprangletop, Leptochloa panicoides (Presl.) Hitchc. # LEFPA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. # BRAPP; rice Oryza sativa L.

Additional index words: Broadleaf herbicides, graminicides, herbicide interactions, Brachiaria platyphylla, Echinochloa crus-galli, Leptochloa panicoides, Oryza sativa.

Abbreviations: UAPB, University of Arkansas at Pine Bluff; WAT, weeks after treatment.

Field experiments were conducted at three locations in 2003 and 2004 to examine clethodim and quizalofop-P efficacy on spring wheat seedlings when applied alone or in tank mixtures with herbicides used to control broadleaf weeds. Clethodim at the recommended rate of 30 g/ha reduced spring wheat biomass by 63 to 98% and was only >90% in three of six site years. In contrast, quizalofop-P at the recommended rate of 36 g/ha reduced wheat biomass >90% in all cases. Clethodim or quizalofop-P could be tank mixed with 2,4-D ester, bromoxynil, or bromoxynil plus MCPA ester with little risk of reduced efficacy on wheat. However, 2,4-D amine was highly antagonistic to both herbicides. The commercial mixture of thifensulfuron plus tribenuron reduced clethodim, but not quizalofop-P, efficacy on wheat. Herbicide options exist for simultaneous control of volunteer glyphosate-resistant canola and glyphosate-resistant wheat if the latter technology were to be commercialized in the future.

Nomenclature: Bromoxynil; clethodim; 2,4-D; MCPA; quizalofop-P; thifensulfuron; tribenuron; canola, Brassica napus L.; wheat, Triticum aestivum L.

Additional index words: Antagonism, glyphosate-resistant crops, herbicide interaction, herbicide mixture, volunteer management.

Abbreviations: ACCase, acetyl-CoA carboxylase (EC 6.4.1.2).

Field studies were conducted to determine the effect of season-long interference of smooth pigweed or livid amaranth on the shoot dry weight and fruit yield of cucumber. Smooth pigweed or livid amaranth densities as low as 1 to 2 weeds per m² caused a 10% yield reduction in cucumber. The biological threshold of smooth pigweed or livid amaranth with cucumber is between 6 to 8 weeds per m². Consequently, weed interference resulted in a reduction in cucumber fruit yield. Smooth pigweed, livid amaranth, and cucumber plant dry weight decreased as weed density increased. Evaluation of smooth pigweed, livid amaranth, and cucumber mean dry weights in interspecific competition studies indicated that cucumber reduced the dry weight of both species of amaranths.

Nomenclature: Smooth pigweed, Amaranthus hybridus #³ AMACH; livid amaranth, Amaranthus lividus # AMALI; cucumber, Cucumis sativus L.

Additional index words: Additive experiment, amaranth, cucumber, weed competition, yield loss.

Five studies were conducted at Clayton, Rocky Mount, and Lewiston-Woodville, NC, in 2001 and 2002, to evaluate weed management, crop tolerance, and yield in strip- and conventional-tillage glyphosate-resistant cotton. Cotton was treated with two glyphosate formulations; glyphosate-IP (isopropylamine salt) or glyphosate-TM (trimethylsulfonium salt), early postemergence (EPOST) alone or in a mixture with S-metolachlor. Early season cotton injury was minimal (3%) with either glyphosate formulation alone or in mixture with S-metolachlor. Weed control and cotton yields were similar for both glyphosate formulations. The addition of S-metolachlor to either glyphosate formulation increased control of broadleaf signalgrass, goosegrass, large crabgrass, and yellow foxtail 14 to 43 percentage points compared with control by glyphosate alone. S-metolachlor was not beneficial for late-season control of entireleaf morningglory, jimsonweed, pitted morningglory, or yellow nutsedge. The addition of S-metolachlor to either glyphosate formulation increased control of common lambsquarters, common ragweed, Palmer amaranth, smooth pigweed, and velvetleaf 6 to 46 percentage points. The addition of a late postemergence-directed (LAYBY) treatment of prometryn plus MSMA increased control to greater than 95% for all weed species regardless of EPOST treatment, and control was similar with or without S-metolachlor EPOST. Cotton lint yield was increased 220 kg/ha with the addition of S-metolachlor to either glyphosate formulation compared with yield from glyphosate alone. The addition of the LAYBY treatment increased yields 250 and 380 kg/ha for glyphosate plus S-metolachlor and glyphosate systems, respectively. S-metolachlor residual activity allowed for an extended window for more effective LAYBY application to smaller weed seedlings instead of weeds that were possibly larger and harder to control.

Nomenclature: Glyphosate-IP (isopropylamine salt); glyphosate-TM (trimethylsulfonium salt); S-metolachlor; MSMA; prometryn; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash. #³ BRAPP; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray. # IPOHG; 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; smooth pigweed, Amaranthus hybridus L. # AMACH; velvetleaf, Abutilon theophrasti Medicus # ABUTH; yellow foxtail, Setaria glauca (L.) Beauv. # SETLU; yellow nutsedge, Cyperus esculentus L. # CYPES; cotton, Gossypium hirsutum L.

Additional index words: Economic returns, herbicide-resistant crops, tillage systems.

Abbreviations: fb, followed by; PDS, postemergence-directed; PREBAN, pre-emergence-banded.

Roots of Canada thistle were excavated from the soil monthly from 1999 to 2001 near Scottsbluff, NE, to quantify the influence of changing soil temperature on free sugars and fructans in roots. Sucrose concentrations were low from May through August then increased in the fall and remained at high levels during winter and then declined in April as plants initiated spring growth. Changes in sucrose, 1-kestose (DP 3) and 1-nystose (DP 4) were shown to be closely associated with changes in soil temperature. During the second year of the study, average soil temperatures during the winter were colder than the first year and resulted in an increase of sucrose in Canada thistle roots. Experiments were conducted from 2001 to 2004 to determine whether there was a correlation between herbicide efficacy, time of herbicide application, and the resulting herbicide effect on root carbohydrate and Canada thistle control. Clopyralid applied in the fall reduced Canada thistle density 92% 8 months after treatment (MAT) whereas treatment made in the spring reduced plant density 33% 11 MAT. Fall application of clopyralid increased the activity of fructan 1-exohydrolase (1-FEH) in roots and was associated with a decline in sucrose, DP 4, and 1-fructofuranosyl-nystose (DP 5) 35 d after treatment (DAT). Spring application of clopyralid also resulted in a decrease of the same carbohydrates 35 DAT, but by 98 DAT, or early October, sucrose level in roots had recovered and was similar to nontreated plants. Fall application of 2,4-D or clopyralid reduced Canada thistle density 39 and 92% respectively, 8 MAT, but only clopyralid resulted in a reduction of sucrose, DP 4, DP 5, and total sugar and an increase of 1-FEH compared with nontreated plants.

Nomenclature: Clopyralid; dicamba; 2,4-D; glyphosate; Canada thistle, Cirsium arvense (L) Scop. #³ CIRAR.

Additional index words: Fructan, fructose, glucose, inulin, sucrose.

Abbreviations: AR(1), first-order autoregressive; 1-FFT, fructan:fructan 1-fructosyl transferase (EC 2.4.1.99); 1-SST, sucrose:sucrose 1-fructosyl transferase (EC 2.4.1.99); DP, degree of polymerization; FW, fresh weight; HPLC, high-performance liquid chromatograph; HPAEC-PAD, high-performance anion-exchange chromatography–pulsed amperometric detector.

Field research was conducted for 3 yr to evaluate crop response and weed control under conventional and reduced tillage in drill- and water-seeded imidazolinone-tolerant (IT) rice culture. Imazethapyr was applied at 70 g ai/ha PRE followed by (fb) imazethapyr at 70 g/ha applied POST to three- to four-leaf rice or at 105 g/ha PRE fb 70 g/ha POST. In both conventional and reduced tillage systems, imazethapyr applied PRE fb POST at 70 g ai/ha controlled red rice, barnyardgrass, Amazon sprangletop, and rice flatsedge 87 to 99% 35 d after POST treatment (DAT). At 35 DAT, Indian jointvetch control with sequential applications of imazethapyr was as high as 70% in water-seeded rice but no more than 54% in drill-seeded rice. Tillage, seeding method, and imazethapyr rate had no effect on days to 50% heading, seeds per panicle, seed weight per panicle, or percentage of seed harvest. However, a reduction of 27% in days to 50% heading, 80% in seeds per panicle, 84% in seed weight per panicle, and 100% in percentage seed harvest index occurred when imazethapyr was not applied because of weed interference. Culm number was reduced 28%, and culm weight 32% under reduced tillage compared with conventional tillage. With sequential applications of imazethapyr at 70 g/ha, rice yield was 63% greater when rice was water-seeded compared with drill-seeded. No differences in tillage systems for weed control, days to 50% heading, seed number, seed weight per panicle, percent seed, panicle height, lodging, or yield were observed. Results of these experiments demonstrate imazethapyr will effectively control weeds in both water- and drill-seeded rice and that reduced tillage can be used without negatively affecting rice production.

Nomenclature: Imazethapyr; Amazon sprangletop, Leptochloa panicoides (Presl) Hitchc. #³ LEFPA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCG; Indian jointvetch, Aeschynomene indica L. # AESIN; red rice, Oryza sativa L. # ORYSA; rice flatsedge, Cyperus iria L. # CYPIR; rice, Oryza sativa L. ‘93-AS-3510’, ‘CL121’.

Additional index words: Conventional tillage, crop injury, drill-seeded rice, reduced tillage, water-seeded rice.

Abbreviations: ALS, acetolactate synthase (E.C.4.1.3.18).

The suitability of a bioherbicide as a component of an integrated weed management program not only relies on its field efficacy, but also on its compatibility with other pest control measures that may be employed during the cropping season. The effects of selected pesticides applied according to label rates on Dactylaria higginsii, a biological control agent for purple nutsedge, were determined using mycelial growth on pesticide-amended potato dextrose agar (PDA) and conidial germination as indicators of pesticide sensitivity. Among the pesticides tested, the herbicides oxyfluorfen and sethoxydim and the fungicides fosetyl-Al and thiophanate methyl inhibited D. higginsii mycelial growth and reduced or completely inhibited conidial germination; the herbicide diuron, the fungicides metalaxyl and copper hydroxide, and the insecticide cyromazine reduced mycelial growth but did not reduce conidial germination. The miticide dicofol reduced mycelial growth and completely inhibited conidial germination while the herbicide imazapyr had no adverse effect on either the mycelial growth or conidial germination of D. higginsii.

Nomenclature: Copper hydroxide; cyromazine; dicofol; diuron; fosetyl-Al, Aluminum tris (ethyl phosphonate); imazapyr; metalaxyl; oxyfluorfen; sethoxydim; thiophanate methyl; purple nutsedge, Cyperus rotundus L. #³ CYPRO, Dactylaria higginsii (Lutrell) M. B. Ellis.

Additional index words: Biological control, bioherbicide, pesticide sensitivity, conidial germination.

Abbreviations: CRD, complete randomized design; RPA, rice polish agar.

Volunteer corn in soybean can reduce yields, interfere with harvest, and cause unacceptable levels of contamination by its presence in the harvested soybean. In Ontario, soybean frequently follow corn in rotation. The use of glyphosate-resistant corn and soybean varieties has increased dramatically in Ontario. Field studies were conducted at two locations in southwestern Ontario to determine whether quizalofop-p-ethyl, clethodim, and fenoxaprop-p-ethyl can be tank mixed with glyphosate to provide effective control of volunteer glyphosate-resistant corn in glyphosate-resistant soybean. Soybean plots were overseeded with glyphosate-resistant corn and treatments consisting of glyphosate applied alone and tank mixed with full and reduced rates of each graminicide with and without a recommended surfactant. Tank mixing the graminicides and adjuvants with glyphosate did not affect glyphosate weed control or crop tolerance. Use of a recommended adjuvant significantly improved the effectiveness of the graminicides, particularly when reduced rates were applied. Quizalofop-p-ethyl was the most effective graminicide for controlling glyphosate-resistant volunteer corn, followed by clethodim and fenoxaprop-p-ethyl.

Nomenclature: Soybean, Glycine max (L.) Merr. ‘Pioneer 9294 RR’; volunteer corn, Zea mays L.

Additional index words: Graminicides, efficacy.

Abbreviation: DAT, days after treatment.

Photosystem II (PS II) inhibitors halt electron flow within the photosynthetic electron transport chain, thereby leading to increased oxidative stress. As a result, their addition to mesotrione, which inhibits carotenoid biosynthesis by inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD), is complementary. Field and greenhouse experiments were conducted in 2002 and 2003 to investigate the joint action of POST mesotrione plus PS II inhibitor herbicide combinations. The joint action of mesotrione plus PS II inhibitors was investigated across five plant species, three PS II inhibitors, and two moisture environments to determine their influence on the joint action response. Rates of mesotrione evaluated ranged from 4.4 to 87.6 g ai/ha alone and in combination with reduced rates of atrazine, bromoxynil, and metribuzin. In the field, all combinations of mesotrione at 8.8, 17.5, and 35.0 g/ha plus atrazine, bromoxynil, or metribuzin were synergistic for necrosis 6 d after treatment (DAT) on sunflower. Addition of atrazine at 280 g/ha to mesotrione at 8.8 g/ha increased velvetleaf leaf necrosis by 18 to 47%. In the greenhouse, the addition of bromoxynil at 70 g/ha to mesotrione at 17.5 g/ha increased leaf necrosis by 23 to 34% and biomass reduction by 38 to 47%. Synergism on Palmer amaranth occurred similarly under both normal and dry moisture environments at application. Plant height at application was found to influence detection of synergism on the whole-plant level.

Nomenclature: Atrazine; bromoxynil; mesotrione; metribuzin; Palmer amaranth, Amaranthus palmeri (S.) Wats. #³ AMAPA; velvetleaf, Abutilon theophrasti Medicus # ABUTH; tame sunflower, Helianthus annuus L. # HELAN.

Additional index words: Interaction, joint action, synergism, carotenoid biosynthesis inhibitor, photosynthesis inhibitor, triketone herbicides.

Abbreviations: ADM, additive dose model; DAP, days after planting; MSM, multiplicative survival model; PET, photosynthetic electron transport; PPFD, photosynthetic photon flux density; PQ, plastoquinone; RCBD, randomized complete-block design; SWC, soil water content.