Rates Of Imazethapyr Research Articles

Interactions between reduced rate of imazethapyr and multiple weed species–soyabean interference in a semi‐arid environment

Yousefi AR, Gonzalez‐Andujar JL, Alizadeh H, Baghestani MA, Rahimian H & Karimmojeni H (2012). Interactions between reduced rate of imazethapyr and multiple weed species–soyabean interference in a semi‐arid environment. Weed Research.52, 242–251.SummaryField experiments were conducted to evaluate Xanthium strumarium and Amaranthus retroflexus competitive ability with soyabean under unsprayed and sprayed (half the recommended rate of imazethapyr) conditions. Weed density combinations of 0, 4, 8 or 12 plants m−1 of row for A. retroflexus and 0, 2, 4 or 8 plants m−1 of row for X. strumarium were established alone, and in all possible combinations. When X. strumarium and A. retroflexus were grown at the same density, X. strumarium contributed 60–69% of the total weed biomass depending on weed density. The half rate of imazethapyr reduced the biomass of both weed species by 90% as compared with untreated plots. Untreated A. retroflexus and X. strumarium reduced soyabean yields to 1911 kg and 1656 kg ha−1, respectively, while with the reduced rate of herbicide, the yield only decreased to 3612 kg and 3453 kg ha−1 respectively. The total weed density required to cause a 5% soyabean yield loss was 0.16 and 0.32 plants m−1 of row with no‐herbicide treatment, while with the half rate of imazethapyr, it increased up to 2.78 and 4.32 plants m−1 in 2007 and 2008 respectively. Owing to the higher competitive ability of X. strumarium, it should be given a greater priority for control than A. retroflexus in soyabean grown in a semi‐arid environment. The half rate of herbicide significantly decreased the competitive ability of X. strumarium and A. retroflexus indicating that, in soyabean, application of this rate might be more cost‐effective and more environment‐friendly than the recommended ones.

Economic Evaluations of Imazethapyr Rates and Timings on Rice

Field studies were conducted in Crowley, LA, and Stoneville, MS, in drill-seeded rice to evaluate economical returns of weed control with imazethapyr. Red rice and barnyardgrass control was evaluated with imazethapyr alone at various rates and application timings. Imazethapyr, averaged across rate, controlled red rice 89% and barnyardgrass 90% when the initial application of imazethapyr was applied at emergence followed by a second application of imazethapyr 2 wk later. No difference in red rice and barnyardgrass control was observed with imazethapyr, averaged across timing. Yield and economical returns were maximized when the initial application of imazethapyr was applied at rice emergence followed by a second application of imazethapyr 2 wk later.

Influence of Simulated Imazapic and Imazethapyr Herbicide Carryover on Cotton (Gossypium hirsutumL.)

Field studies were conducted during the 2001 and 2002 growing seasons in the Texas peanut growing regions to simulate residual concentrations of imazapic and imazethapyr in the soil and subsequent effects on cotton (Gossypium hirsutumL.). Simulated imazapic or imazethapyr rates included 0, 1/64X (1.09 g ai/ha), 1/32X (2.19 g ai/ha), 1/16X (4.38 g ai/ha), 1/8X (8.75 g ai/ha), 1/4X (17.5 g ai/ha), and 1/2X (35 g ai/ha) of the full labeled rate for peanut (Arachis hypogaeaL.) and incorporated prior to cotton planting. Cotton stunting with imazapic or imazethapyr was more severe at Denver City than other locations. All rates of imazapic and imazethapyr resulted in cotton stunting at Denver City while at Munday and Yoakum the 1/8X, 1/4X, and 1/2X rates of imazapic resulted in reduced cotton growth when compared with the untreated check. At all locations imazapic caused more stunted cotton than imazethapyr. Cotton lint yield was reduced by imazapic or imazethapyr at 1/4 X and 1/2 X rates at all locations when compared with the untreated check.

Postemergence Weed Control in Peanut Using Reduced Rate or Combinations of Imazapic and Imazethapyr

Studies were conducted in different Texas peanut (Arachis hypogaea L.) production regions to evaluate POST applications of imazapic and imazethapyr at ½× (0.035 kg ai/ha) or 1× (0.07 kg ai/ha) of the manufacturers' suggested use rate and in combination with acifluorfen at 0.42 kg ai/ha, acifluorfen at 0.105 kg ai/ha plus bentazon at 0.05 kg ai/ha, or 2,4-DB at 0.28 kg ai/ha. Palmer amaranth (Amaranthus palmeri S. Wats) control was most consistent with imazapic or imazethapyr plus 2,4-DB. Imazapic in combination with 2,4-DB or acifluorfen plus bentazon controlled ivyleaf morningglory [Ipomoea hederacea (L.) Jacq] at least 75%. Smellmelon (Cucumis melo L. var. Dudaim Naud.) control was at least 95% with 1× imazapic. Imazapic at 1× in combination with acifluorfen controlled desert horse purslane (Trianthema portulacastrum L.) over 90%. No peanut stunting was noted at Yoakum with any treatment; however, at Lamesa, Lockett, and Quitaque peanut stunting was noted. Although 1× imazapic or imazethapyr provided slightly more consistent weed control than the ½× rate, peanut yield did not increase with higher rate. Therefore, growers may be able to reduce production costs with lower rates of imazapic or imazethapyr.

Problem Weed Control in Glyphosate-Resistant Soybean with Glyphosate Tank Mixes and Soil-Applied Herbicides

Although glyphosate controls many plant species, certain broadleaf weeds in Nebraska's cropping systems exhibit various levels of tolerance to the labeled rates of this herbicide, including ivyleaf morningglory, Venice mallow, yellow sweetclover, common lambsquarters, velvetleaf, kochia, Russian thistle, and field bindweed. Therefore, two field studies were conducted in 2004 and 2005 at Concord and North Platte, NE, to evaluate performance of (1) seven preemergence (PRE) herbicides and (2) glyphosate tank mixes applied postemergence (POST) at three application times for control of eight weed species that are perceived as problem weeds in glyphosate-resistant soybean in Nebraska. The PRE herbicides, including sulfentrazone plus chlorimuron, pendimethalin plus imazethapyr, imazaquin, and pendimethalin plus imazethapyr plus imazaquin provided more than 85% control of most weed species tested in this study 28 d after treatment (DAT). However, sulfentrazone plus chlorimuron and pendimethalin plus imazethapyr plus imazaquin were the only PRE treatments that provided more than 80% control of most weed species 60 DAT. In the POST glyphosate tank-mix study, the level of weed control was significantly affected by the timing of herbicide application; control generally decreased as weed height increased. In general, glyphosate tank mixes applied at the first two application times (early or mid-POST) with half label rates of lactofen, imazamox, imazethapyr, fomesafen, imazaquin, or acifluorfen, provided more than 80% control of all species that were 20 to 30 cm tall except ivyleaf morningglory, Venice mallow, yellow sweetclover, and field bindweed. Glyphosate tank mixes applied late POST with lactofen, imazethapyr, or imazaquin provided more than 70% control of common lambsquarters, velvetleaf, kochia, and Russian thistle that were 30 to 50 cm tall. Overall, glyphosate tank mixes with half label rates of chlorimuron or acifluorfen were the best treatments; they provided more than 80% control of all the studied weed species when applied at early growth stages. Results of this study suggested that mixing glyphosate with other POST broadleaf herbicides, or utilizing soil-applied herbicides after crop planting helped effectively control most problematic weeds in glyphosate-resistant soybean in Nebraska.

The blend modification of EVA-150/ starch and controlled-release of imazethapyr

The EVA-150 and starch were extruded by extruding press and the bio-degradation composite material was prepared to use as the controlled-release matrix of imazethapyr. The compatibility and crystallinity of EVA-150/starch blending were analyzed by SEM and DSC, and the controlled-released performance of imazethapyr in the carriers was also investigated by UV analysis. The results show that EVA-150/starch composite matrix has the obvious controlled-released function and the release rates of imazethapyr all exceed 50% in the environment of pH4, pH7, or pH9 after nine days.

Weed control in cowpea (<i>Vigna unguiculata</i> (L) Walp) with imidazolinone herbicide mixtures

Field experiments were conducted between 1994 and 1997 at the University of Ilorin Teaching and Research Farm, Ilorin (8o29`N; 4o35`E), in the southern Guinea savanna agro-ecological zone, to evaluate the efficacy of pre-emergence applications of two imidazolinone-based herbicide mixtures in cowpea ( Vigna unguiculata ) fields. Different rates of imazethapyr [(±)2-[4,5 dihydro-4-methyl-4-(1-methylethyl)-5-oxo-IH-imidazol-2-yl]5-ethyl-3 pyridine carboxylic acid] +pendimethalin (N-(1-ethylpropyl)-3,4dimethyl-2,6 dinitrobenzenamine)[Pursuit Plus]1 and imazaquin [2,[4,5-dihydro-4-methyl-4(1-methylethyl)-5-oxo-1H-imidazol-2-yl]3-quinoline carboxylic acid] + pendimethalin [Squadron]2 were compared with weedy or hand weeded control treatments, as well as with one or two rates of metolachlor [2-chloro-N-(2-ethyl –6-methylphenyl)-N-(2-methoxy-1-1 methyethyl) acetamide] + metobromuron[NI-(4- bromophenyl)N-methoxy-N-methylurea] (Galex)3, a standard herbicide recommendation for the crop. Each of the trials was designed as a randomized complete block with three or four replications. Results showed that various rates of the herbicide mixtures effectively controlled weeds in cowpea fields for between 6 and 10 weeks after planting (wap). Pursuit plus was generally more effective than Squadron at comparable rates of application, just as the tank mixtures of imazaquin+ pendimethalin were more effective than their formulated mixture (Squadron) at equivalent rates in the final trial. There was a significant positive correlation between weed control rating (wcr) and cowpea grain yield. The overall best treatment with regard to weed control and grain yield was Pursuit plus at 0.99 kg ai/ha, while the best rate of Squadron, based on the same criteria, was 1.02 kg ai/ha. Uncontrolled weed growth resulted in 45-59% reductions in grain yield. None of the herbicide mixtures was able to effectively control Vernonia galamensis and Paspalum orbiculare, while only Pursuit plus and a relatively high rate of Squadron (1.54 kg ai/ha) effectively controlled Tridax procumbens. Keywords : dinitroaniline, imidazolinone, weed control rating, Vernonia galamensis , Paspalum orbiculare, Tridax procumbens JARD Vol. 4 (2) 2005: pp. 104-121

Amino Acid Substitutions in the Acetolactate Synthase Gene of Red Rice (Oryza sativa) Confer Resistance to Imazethapyr

Two red rice accessions from Arkansas have been found to be resistant to the labeled rate of imazethapyr, which is used to control red rice in ClearfieldTMrice. Full-length amplification of the acetolactate synthase (ALS) gene in imazethapyr-resistant red rice revealed a coding sequence of 1,935 base pairs, which is the same as that of the cultivated rice. Coding sequences were generated from four red rice accessions collected from different geographical regions in Arkansas, consisting of accessions that were either resistant or susceptible to imazethapyr. Nucleotide sequence alignments identified six base polymorphisms, three of which resulted in amino acid substitutions in theALSgene. One amino acid substitution, Gly654Glu, involves a residue required for imazethapyr binding to the ALS. The other substitution, Val669Met, implies conformational changes in the ALS structure that enhances binding of thiamine diphosphate, an ALS cofactor. These novel amino acid substitutions first reported for ALS-resistant red rice accessions support the hypothesis that ALS-resistant red rice can evolve with sustained herbicide selection pressure. Thus, it behooves growers to integrate the Cleafield rice technology with other tools to achieve a successful, long-term weed management program.

Field dissipation of prometryn, oxyfluorfen and imazethapyr in Mollisol and Vertisol soils.

Dissipation rate of prometryn, oxyfluorfen and imazethapyr was estimated in the Mollisol San Antón and the Vertisol Fraternidad soil series, both soils from the south semi-arid coastal region of Puerto Rico. The study was carried out in two consecutive years. The herbicides were applied one day after seeding pigeon peas at Juana Díaz (San Antón soil series) and Lajas (Fraternidad soil series) Agricultural Experiment Substations. Herbicide rates were 2.24, 0.28 and 0.070 kg ai/ha for prometryn, oxyfluorfen and imazethapyr, respectively. Soil samples at 15-cm depth were collected at 0, 28, 56,112 and 168 days after application. Field half-lives between 2 and 43, 31 and 88, and 19 and 46 days were found for prometryn, oxyfluorfen and imazethapyr, respectively. Substantial dissipation rate variability for above mentioned herbicides has been shown to occur within the soil and year treatments. These findings suggest very short and variable persistence for the three herbicides in both soils under a tropical climate.

Imazethapyr Use with and without Clomazone for Weed Control in Furrow-Irrigated, Imidazolinone-Tolerant Rice

Research on weed management in furrow-irrigated rice is needed as water availability becomes more limited in rice production regions of Arkansas. Research was conducted at Keiser and Pine Tree, AR, with the objectives being to determine (1) whether the addition of clomazone to imazethapyr would improve PRE weed control in furrow-irrigated, imidazolinone-tolerant rice, and (2) whether increasing the imazethapyr rates would improve weed control without injuring rice. Imazethapyr was applied at 70, 87.5, and 105 g ai/ha PRE with and without clomazone followed by imazethapyr POST at the same rate as used PRE. No rice injury was observed during the growing season at either site. Clomazone plus imazethapyr applied PRE did not improve early season control of Palmer amaranth, pitted morningglory, prickly sida, barnyardgrass, or broadleaf signalgrass over imazethapyr alone. Increasing the PRE imazethapyr rate to 105 g/ha did not improve Palmer amaranth or pitted morningglory control. Imazethapyr applied PRE on a clay soil generally provided lower weed control than on the silt loam soil. Increasing the imazethapyr rate did not improve rice yields.Nomenclature: Clomazone, imazethapyr, barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG, broadleaf signalgrass, Urochloa platyphylla (Nash) R.D. Webster BRAPP. Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA, pitted morningglory, Ipomoea lacunosa L. IPOLA, prickly sida, Sida spinosa L. SIDSP, rice, Oryza sativa L. ‘CL 730’ ORYSA

Weed control, environmental impact and profitability of reduced rates of imazethapyr in combination with dimethenamid in dry beans

Field experiments were conducted from 2003 to 2005 in Ontario to determine if reduced rates of imazethapyr (< 75 g a.i. ha-1) tank-mixed with dimethenamid applied preemergence (PRE) can be used as a feasible weed management strategy for broad-spectrum weed control in white and kidney beans (Phaseolus vulgaris L.). There was no injury in white or kidney bean with the imazethapyr plus dimethenamid tank-mix treatments evaluated. The rate of imazethapyr required to provide adequate control of green foxtail [Setaria viridis (L.) P. Beauv.], lamb’s-quarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.), wild mustard (Sinapis arvensis L.), and redroot pigweed (Amaranthus retroflexus L.) tended to be reduced when tankmixed with dimethenamid at 1000 g ha-1. There was no adverse effect on the yield of white and kidney beans at the highest rate (75 g a.i. ha-1) of imazethapyr evaluated. Although both herbicides are considered reduced risk, the environmental impact of imazethapyr (75 g a.i. ha-1) was seven times less than that of dimethenamid (1000 g a.i. ha-1). The addition of reduced rates of imazethapyr to dimethenamid did not significantly increase environmental impact (EI) vs. dimethenamid alone. Profit margins were greater when dimethenamid was tank-mixed with imazethapyr than for applications of imazethapyr alone. Across all treatments, profit margins were maximized at an imazethapyr rate of 60 g a.i. ha-1 for white bean and an imazethapyr rate of between 60 and 75 g a.i. ha-1 for kidney bean. However, the profit-maximizing rates of imazethapyr tended to be higher for treatments without dimethenamid than for treatments where dimethenamid was tank-mixed with imazethapyr. Key words: Dimethenamid, environmental impact quotient (EIQ), imazethapyr, Montcalm, OAC Thunder, Phaseolus vulgaris L., profit margin

Target-site resistance to acetolactate synthase inhibitors in wild mustard (Sinapis arvensis)

Inhibitors of acetolactate synthase (ALS) are important herbicides for control of wild mustard, a common weed of the north central United States and Canada. Wild mustard that survived treatments with the ALS inhibitors cloransulam, imazethapyr, and thifensulfuron was sampled from a North Dakota soybean field in 1999. The mechanism of resistance and response of this wild mustard biotype to ALS-inhibiting herbicides was investigated. In vitro enzyme-inhibition experiments confirmed a resistance mechanism associated with the ALS enzyme; imazethapyr or imazamox at 1 × 10−4M caused only 10 to 11% and 12 to 16% reductions in ALS activity, respectively. ALS from a susceptible wild mustard biotype was inhibited 50% (I50) with imazethapyr at 8 × 10−7M or imazamox at 1.1 × 10−6M. Whole-plant greenhouse treatments confirmed cross-resistance across ALS-inhibitor classes. Treatment with twice-normal field rates of thifensulfuron, ethametsulfuron, triflusulfuron, imazamox, imazethapyr, flumetsulam, cloransulam, flucarbazone, and imazamethabenz reduced biomass of the susceptible biotype at least 96% 28 d after treatment. Biomass of the resistant biotype was reduced 49% by triflusulfuron and 35% by thifensulfuron, but was not reduced by other herbicides. DNA sequence analysis of ALS genes from resistant and susceptible biotypes revealed a point mutation inferring a Trp-to-Leu amino acid substitution in ALS of the resistant biotype. This mutation, corresponding to position 574 of theArabidopsisALS amino acid sequence, is known to confer cross-resistance to ALS-inhibiting herbicides and is the probable cause of resistance in the wild mustard biotype. Phylogenetic analysis of wild mustard and canola ALS sequences confirmed that the Trp574mutation arose within wild mustard and was not derived via introgression from imidazolinone-resistant canola. The results of this research indicate a naturally occurring target-site point mutation responsible for conferring cross-resistance to ALS-inhibiting herbicides in this wild mustard biotype.

Resistance and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides

The frequent application of herbicides in agricultural areas may select resistant biotypes in weed populations, whose biological characteristics influence the speed and patterns of resistance. This research aims to charactere, simultaneously, resistance patterns and differential susceptibility of Bidens pilosa and B. subalternans biotypes to ALS-inhibiting herbicides of the imidazolinone and sulfonylurea chemical groups. Six hairy beggarticks biotypes, four suspected resistant and two known susceptible, were treated with eight rates of chlorimuron-ethyl or imazethapyr, in greenhouse conditions. Percent control and percent fresh weight of the plants were evaluated at 28 days after the application. B. subalternans is less susceptible to ALS-inhibiting herbicides than B. pilosa; B. subalternans biotypes were more resistant than B. pilosa biotypes; there are B. pilosa and B. subalternans biotypes with cross resistance to the ALS-inhibiting herbicides of the sulfonylurea and imidazolinone groups; there are different patterns of cross resistance to the diverse groups of ALS-inhibiting herbicides.

Effect of Cultural Practices on Weed Control and Crop Response in Imidazolinone-Tolerant Rice

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.

Imazethapyr Rate Responses for Wild Radish, Conventional Canola, and Imidazolinone-tolerant Canola

Greenhouse experiments were conducted to determine dose responses to imazethapyr for imidazolinone-tolerant canola (Brassica napus) Pioneer 45A71, conventional canola Oscar, and wild radish (Raphanus raphanistrum). Two weeks after treatment, foliar injury was rated and plants were harvested to determine plant dry weight. Plant responses to herbicide treatments were analyzed by nonlinear regression procedures using a modified Mitscherlich plant growth model for visual injury and the negative exponential growth function for plant dry weight. Pioneer 45A71 was tolerant of all rates of imazethapyr (0.055 to 0.60 g ai/liter). In contrast, wild radish and Oscar were sensitive to imazethapyr with significant injury and approximately 50% reduction in dry plant weight at rates of 0.275 g ai/liter and greater. For the model, increased injury from herbicide treatment resulted in significantly different asymptotic maximum (βo) injury for all plant types. The dry weight for the non-treated control was 1.3, 0.8, and 1.5 g/plant for wild radish, Pioneer 45A71, and Oscar, respectively. For the models, β1 parameters indicated significant differences in response to imazethapyr treatment between the Pioneer 45A71, wild radish, and Oscar dry weights. Accepted for publication 3 July 2006. Published 18 October 2006.

Weed Control in Sericea Lespedeza with Imazethapyr

Field studies were conducted to determine the feasibility of using imazethapyr applied preemergence (PRE) and postemergence (POST) for weed control in sericea lespedeza. In the POST experiment, imazethapyr was applied at 0, 71, 142, and 213 g ai/ha to mature, recently mowed stands of sericea lespedeza. Regardless of rate, yellow nutsedge and cutleaf groundcherry control at 2 mo after treatment, as determined by weed foliage biomass relative to the nontreated plants, was 90 and 80%, respectively. Sericea lespedeza forage yield (weeds removed) was not reduced by POST-applied imazethapyr even at 213 g/ha. The same imazethapyr rates were used with newly seeded sericea lespedeza in the PRE-applied experiment. Imazethapyr at 71 g/ha provided at least 78% control of large crabgrass, stinkgrass, yellow nutsedge, sicklepod, and cutleaf groundcherry as well as maximum sericea lespedeza performance, as indicated by seedling height, weight, and stand count. Results indicated that imazethapyr can be used for either PRE- or POST-applied weed control in sericea lespedeza. However, margin of safety is greater with imazethapyr applied POST to mature stands than with PRE applications to germinating seeds.

Weed Control in Pea with Reduced Rates of Imazethapyr Applied Preemergence and Postemergence1

Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when p...

Soybean response to plant growth regulator herbicides is affected by other postemergence herbicides

Two studies investigated off-target exposure of soybean to plant growth regulator (PGR) herbicides and determined if simultaneous exposure to PGR herbicides and labeled soybean herbicides increase PGR injury. The PGR herbicides, 2,4-D, clopyralid, and dicamba, as well as dicamba plus the auxin transport inhibitor diflufenzopyr, were applied to glyphosate-resistant soybean at the V3, V7, and R2 soybean growth stages. Two rates were chosen from previous and preliminary research to approximate threshold rates that would cause a yield reduction so as to distinguish differences in sensitivity between growth stages. All four PGR herbicides caused significant soybean injury, height reduction, and yield loss at one or more application rates and growth stages. Relative to other PGR herbicides, dicamba reduced soybean yield at the lowest rate (a potential rate from residues remaining in improperly cleaned application equipment), followed by clopyralid, with 2,4-D requiring the highest rate to reduce soybean yield (a potential rate from a high level of spray drift). Dicamba and dicamba plus diflufenzopyr were applied at equal fractions of labeled use rates for corn to compare them directly at equivalent levels of off-target movement. Dicamba plus diflufenzopyr caused less injury and yield loss than dicamba applied alone. In a second study, the highest labeled soybean use rates of glyphosate, imazethapyr, imazamox, and fomesafen were applied alone and in combination with the highest rate of dicamba used in the first study (1% of a labeled use rate for corn) at the V3 and V7 stages. Dicamba demonstrated synergistic interactions with imazamox, imazethapyr, and fomesafen (but not with glyphosate) to further reduce yield under some circumstances, especially when applied at the V7 stage. Several treatments that included dicamba reduced soybean seed weight when applied at either the V3 or V7 stage and reduced the number of seeds per pod at the V7 stage.

Use of Optical Remote Sensing for Detecting Herbicide Injury in Soybean

Experiments were conducted from 2000 to 2002 at two locations each year to determine if lactofen and imazethapyr injury to soybean could be detected using digital aerial imagery and ground-based optical remote sensing. Lactofen and imazethapyr were applied at base rates of 105 and 71 g/ha, respectively, and at 0, 2X, and 4X rates. Treated plots were evaluated between 7 and 21 d after treatment for crop injury using a ground-based radiometer and a system using computer analysis of digital aerial imagery. Both the ground-based radiometer and the digital aerial imagery were effective in detecting herbicide injury under most conditions. The digital aerial imagery system was found to be more sensitive in detecting herbicide injury than the ground-based radiometer system. Herbicide or herbicide rate had a significant effect on normalized differential vegetation indices (NDVI) derived from digital aerial imagery in four of four site-years. NDVI values derived from a multispectral ground-based radiometer were significant for herbicide or herbicide rate in four of six site-years. NDVI values from treated plots were subtracted from the NDVI value of the untreated check to generate a ΔNDVI. The resulting ΔNDVI values from the ground-based radiometer system were significant for herbicide or herbicide rate in six of six site-years. Neither optical remote-sensing system was effective at estimating actual application rates of lactofen and imazethapyr across a broad range of field and weather conditions due to temporal and spatial variability in crop response to the herbicides.

Grain Sorghum Response to Simulated Drift from Glufosinate, Glyphosate, Imazethapyr, and Sethoxydim1

Field experiments were conducted at four locations in Kansas in 1999 and 2000 to evaluate grain sorghum response to simulated drift rates of four herbicides. Imazethapyr, glufosinate, glyphosate, and sethoxydim were applied at 1/3, 1/10, 1/33, and 1/100 of the use rate when plants were 10 to 20 cm tall. Visible crop injury increased as rates of each herbicide increased. Glyphosate and imazethapyr caused the most injury and glufosinate the least. Data show that some plants that were significantly injured 2 wk after treatment (WAT) recovered 8 WAT. However, some plants that received the highest rate of imazethapyr or glyphosate died. Grain sorghum yields were reduced only when injury was severe. This research showed that the potential for sorghum injury from off-target herbicide drift is greater from imazethapyr and glyphosate than from sethoxydim or glufosinate. Nomenclature: Glufosinate; glyphosate; imazethapyr; sethoxydim; sorghum, Sorghum bicolor (L.) Moench. Additional index words: Crop injury, herbici...