A study was conducted in 2001 and 2002 in Texas to evaluate red rice control and crop response of imidazolinone-tolerant rice with imazethapyr on coarse-textured soils. Because imazethapyr was not registered for use on imidazolinone-tolerant rice on coarse-textured soils in Texas, crop response was evaluated to determine whether imidazolinone-tolerant rice yields would be reduced with sequential applications of imazethapyr on soils having greater than 50% sand content. The treatment factors consisted of preemergence (PRE) applications of imazethapyr at 50, 70, or 87 g ai/ ha followed by (fb) preflood (PREFLD) applications of 35 or 50 g/ha. Imazethapyr at 70 g/ha PRE fb 70 g/ha PREFLD was added as a seventh treatment. PRE applications were activated by rainfall or surface irrigation after application, and PREFLD applications were sprayed 1 to 2 d before application of the permanent flood. In both years, 100% red rice control was achieved with all rate combinations. Early-season visual rice injury ranged from 5 to 21% and did not result in yield losses, indicating that imazethapyr is safe on coarse-textured soils.

Field studies were conducted to assess two sulfur-containing additives for use with glyphosate applied postemergence to glyphosate-resistant cotton for the control of sicklepod and yellow nutsedge. Neither diammonium sulfate (AMS) nor ammonium thiosulfate (ATS), both applied at 2.24 kg/ha, increased control of either species. Effective control of both species was dependent on glyphosate (isopropylamine salt) rate alone, with optimum control at 1.26 kg ae/ha. Plant-mapping data further indicated that sulfur-containing additives generally had no effect on either cotton fruiting patterns or yield. However, applying glyphosate at any rate did increase seed cotton yield in 2 of 3 yr vs. no glyphosate. In addition, applying glyphosate at any rate resulted in an increase in the number of bolls vs. no glyphosate in the following plant-mapping responses: total number of bolls per plant, number of abcised bolls per plant, bolls at the top five sympodial nodes, and bolls at positions 1 and 2 on the sympodia. Glyphosate absorption and subsequent translocation, as influenced by the addition of the sulfur-containing additives, was evaluated using radiotracer techniques. Glyphosate absorption after 48 h was 86, 63, and 37% of amount applied in cotton, sicklepod, and yellow nutsedge, respectively. Absorption by sicklepod and yellow nutsedge was not affected by the addition of either of the additives. Absorption by cotton was reduced by ATS but was not affected by AMS. In yellow nutsedge and cotton, glyphosate concentration in the treated area and adjacent tissue was not affected by either additive. A greater portion of glyphosate was translocated away from the treated area in sicklepod with glyphosate plus AMS (32%) than with glyphosate plus ATS (21%). AMS and ATS may be used in glyphosate-resistant cotton without the risk of either crop injury or yield reduction. However, their use for increased control of annual weed species, such as sicklepod and yellow nutsedge, may not be warranted.

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

Field experiments were conducted on two North Carolina research stations in 1999, 2000, and 2001; on-farm in Lenoir, Wayne, and Wilson counties, NC, in 2002; and on-farm in Port Royal, VA, in 2000, 2001, and 2002 to evaluate possible gains from site-specific herbicide applications at these locations. Fields were scouted for weed populations using custom software on a handheld computer linked to a Global Positioning System. Scouts generated field-specific sampling grids and recorded weed density information for each grid cell. The decision aid HADSS™ (Herbicide Application Decision Support System) was used to estimate expected net return and yield loss remaining after treatment in each sample grid of every field under differing assumptions of weed size and soil moisture conditions, assuming the field was planted with either conventional or glyphosate-resistant (GR) soybean. The optimal whole-field treatment (that treatment with the highest expected net return summed across all grid cells within a field) resulted in average theoretical net returns of $79/ha (U.S. dollars) and $139/ha for conventional and GR soybean, respectively. When the most economical treatment for each grid cell was used in site-specific weed management, theoretical net returns increased by $13/ha (conventional) and $4.50/ha (GR), and expected yield loss after treatment was reduced by 10.5 and 4%, respectively, compared with the whole-field optimal treatment. When the most effective treatment for each grid cell was used in site-specific weed management, theoretical net returns decreased by $18/ha (conventional) and $4/ha (GR), and expected yield loss after treatment was reduced by 27 and 19%, respectively, compared with the whole-field optimal treatment. Site-specific herbicide applications could have reduced the volume of herbicides sprayed by as much as 70% in some situations but increased herbicide amounts in others. On average, the whole-field treatment was optimal in terms of net return for only 35% (conventional) and 57% (GR) of grid cells.

Seed production from weeds that are missed by herbicide application can affect future weed populations and management decisions. It may be possible to expand the utility of computerized weed management decision aids to include an estimate of weed seed production resulting from selected treatments based on crop yield potential. Field studies were conducted in soybean near Columbia, MO, to determine whether weed control recommendations based on crop yield potential from a computerized weed management decision aid influence weed seed production in two soybean row spacings. At approximately 28 d after planting, weed densities and heights were entered into WeedSOFT® to generate a list of treatments ranked by predicted crop yields. Treatments included: (1) highest predicted crop yield in a glyphosate-resistant system, (2) highest predicted crop yield in a nonglyphosate-resistant system, (3) a 10% yield reduction, (4) a 20% yield reduction, and (5) an untreated control. These treatments were applied to soybean grown in 38- and 76-cm rows. Treatments that provided 90% or higher control of an individual species at 22 d after treatment usually produced less seed than untreated checks. Weed seed production based on early-season herbicide efficacy showed a linear relationship and was relatively predictable (r2 ≥ 0.52) for the predominant weed species. For less dominant weed species, weed seed production was not strongly correlated (r2 ≤ 0.27) to early-season herbicide efficacy but apparently influenced by control of other weed species. Narrow row spacing reduced giant foxtail biomass both years but did not reduce common ragweed and ivyleaf morningglory biomass. Narrow rows did not decrease giant foxtail, common ragweed, and ivyleaf morningglory seed production.

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

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control.

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

Field studies were conducted in Arkansas in 1999, 2000, and 2001 to evaluate mesotrione applied preemergence (PRE) and postemergence (POST) for weed control in corn grown in the Mississippi Delta region of the United States. Mesotrione was applied PRE (140, 210, and 280 g/ha) alone and POST (70, 105, and 140 g/ha), alone or in tank mixtures with atrazine (280 g/ha). Standard treatments for comparison were S-metolachlor/atrazine PRE and S-metolachlor plus atrazine PRE followed by atrazine POST. All PRE treatments controlled velvetleaf, pitted morningglory, entireleaf morningglory, prickly sida, and broadleaf signalgrass 95% 2 wk after emergence (WAE). Mesotrione controlled velvetleaf 89% or more 4 and 6 WAE. Control of morningglory species by mesotrione POST averaged 92% 6 WAE. Prickly sida was controlled at least 90% by all treatments 4 WAE. Mesotrione applied alone PRE and POST controlled broadleaf signalgrass 83 to 91% 4 WAE. All treatments controlled broadleaf signalgrass less than 90% 6 WAE, except treatments that contained S-metolachlor, which gave 94% or greater control. Corn yield ranged from 10.5 to 12.4 Mg/ha and did not differ among treatments. Mesotrione PRE and POST provided excellent control of broadleaf weeds, but S-metolachlor was needed for broadleaf signalgrass control.

Uncontrolled kochia plants that regrow after small-grain harvest can produce substantial numbers of seeds. An average of 4,100 seeds per plant were produced between harvest (late July to mid August) and the first killing frost (late September) at three locations in Montana. Field experiments were conducted to determine the optimal timing of postharvest herbicide applications to prevent kochia from producing viable seeds. Herbicide treatments were applied at three timings from late August to mid September. The most effective treatments were glyphosate (631 g/ha) and paraquat (701 g/ha) applied at the second application timing (late August to early September). These treatments reduced kochia seed production by 92% or greater at each site. Kochia regrowth by this time had sufficient leaf area for herbicide absorption, but few viable seed had been produced. Herbicide treatments at the first and third application timings were generally less effective and more variable in reducing kochia seed production. Sulfentrazone (157 g/ha) and 2,4-D (561 g/ha) were not as effective at reducing seed production as other herbicide treatments.

Field studies were conducted near Knoxville, TN, during late March and early April 2002 and 2003, respectively, for star-of-Bethlehem control in dormant bermudagrass turf that was established over 25 yr ago. Halosulfuron, imazaquin, metsulfuron, 2,4-D plus dicamba plus mecoprop, and triclopyr plus clopyralid controlled star-of-Bethlehem 35% at most 35 d after treatment (DAT). Bromoxynil alone or mixed with halosulfuron, imazaquin, or metsulfuron controlled star-of-Bethlehem at least 80% at 35 DAT. Imazaquin and imazaquin plus bromoxynil injured bermudagrass 51% 35 DAT. This injury was characterized by decreased bermudagrass postdormancy transition and was transient.

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

Tropical soda apple samples were collected from 31 populations across the southeastern United States and from four populations in a portion of its native range in Brazil. The genetic relationships among these populations were examined by single primer amplification reactions (SPAR) and by sequencing a portion of the chloroplast genome. SPAR revealed no variation among the 132 individuals and only two chloroplast haplotypes were detected in the 50 individuals sequenced. The most common haplotype was present in all samples from the United States and most of the Brazilian samples, whereas the second haplotype was only found in one of the Brazilian populations. Within the limitations of these data, we conclude that Brazil is the best location to seek a potential biological control agent for tropical soda apple, and that, if identified, this agent should prove useful for populations throughout the United States.

Tropical spiderwort has recently become the most troublesome weed in Georgia cotton. Most of Georgia's cotton is glyphosate resistant (GR), and glyphosate is only marginally effective on tropical spiderwort. An experiment was conducted at four locations to determine tropical spiderwort control in GR cotton by 27 herbicide systems. Treatments consisted of three early-postemergence over-the-top (POT) herbicide options and nine late–postemergence-directed (LPD) options arranged factorially. Glyphosate POT controlled tropical spiderwort only 53% 21 d after treatment (DAT). Glyphosate plus pyrithiobac or S-metolachlor controlled tropical spiderwort 60 and 80%, respectively. Pyrithiobac improved control of emerged spiderwort, whereas S-metolachlor provided residual control. Pooled over POT treatments, glyphosate LPD controlled tropical spiderwort 70% 21 DAT. Dimethipin mixed with glyphosate did not improve control. Carfentrazone, diuron, or flumioxazin mixed with glyphosate LPD improved control 9 to 15%. MSMA and MSMA plus flumioxazin were 8 and 19% more effective than glyphosate LPD. At time of cotton harvest, systems without residual herbicides at LPD controlled tropical spiderwort 42 to 45% compared with 64 to 76% with LPD treatments that included diuron or flumioxazin.

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

Crop injury caused by drift of auxin-like herbicides has been a concern since their development. Research was conducted to describe a method of quantifying injury from auxin-like herbicides as a first step in determining crop damage. Reduced rates of 2,4-D, dicamba, and triclopyr were applied to cotton and soybean plants in the three- to six-leaf stage in field and greenhouse studies. Injury to leaves and stems were evaluated separately, and the values were combined so that one injury estimate was obtained for each individual plant rated. Injury symptoms were typical for auxin-type herbicides and ranged from slight bending of stems or petioles and wrinkled leaves to necrosis. Specific descriptions of leaf and stem injury levels were used to describe plant injury consistently. These descriptions were very detailed for the lower injury levels, but the characterizations became more general as the injury increased because of the prominence of factors such as necrosis. The injury evaluation method provided repeatable results for each herbicide and herbicide rate used. This injury evaluation method has many possible uses in auxin-like herbicide research and lays the foundation for forecasting the impact of early-season injury to cotton and soybean yield.

Brazilian pepper is a small evergreen tree that forms dense colonies. It was introduced for horticultural use in the United States in the early 1800s and was widely distributed in Florida in the late 1920s. Previous remote-sensing projects to detect Brazilian pepper achieved moderate success and warranted additional research using a hyperspectral sensor. Detection with remote sensing is desirable because complete access to ground survey crews is not practical. The western half of the Everglades National Park was imaged at a 5-m spatial resolution with a hyperspectral sensor by Earth Search Sciences Inc. of Kalispell, MT, on December 12, 2000, and January 10, 2001. The sensor has 128 channels and spectral resolution between 450 and 2,500 nm. The purpose of this research was to develop spectral reflectance curves for Brazilian pepper and establish the accuracy of classified images. Classified images showed that a hyperspectral sensor could detect a “pure” Brazilian pepper pixel representing the center of an infestation but not “mixed” Brazilian pepper pixels at the sparsely populated edges. To define the sparse populations, images were classified using a spatial buffer (15- to 100-m radius) based on a low–omissional error image. A 25-m buffer reduced the amount of commissional error for Brazilian pepper in mangrove-dominated forest to 8.2% and buttonwood-dominated forest to 0%. Wider buffers did not significantly improve image accuracy when compared with the 25-m buffer distance. Results indicate that removal crews using hyperspectral images will be able to reliably find the colonies of Brazilian pepper but will not be able to use the images to find isolated scattered trees.

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

Thirteen field trials were conducted in 1999 and 2000 to evaluate postemergence (POST) weed control with single applications of bromoxynil at 420 or 560 g ai/ha, glufosinate at 291 or 409 g ai/ha, glyphosate at 1,120 g ai/ha, pyrithiobac at 36 or 72 g ai/ha, or sulfosate at 1,120 g ai/ha. Additional treatments evaluated included two applications with glufosinate at both rates in all possible combinations, two applications of glyphosate, and two applications of sulfosate. Weeds were 2 to 5 cm or 8 to 10 cm tall for annual grass and broadleaf weeds whereas yellow nutsedge and glyphosate-resistant corn were 8 to 10 cm tall. All herbicide treatments controlled 2- to 5-cm common cocklebur, Florida beggarweed, jimsonweed, ladysthumb smartweed, Pennsylvania smartweed, pitted morningglory, prickly sida, redroot pigweed, smooth pigweed, and velvetleaf at least 90%. All herbicide treatments except pyrithiobac at either rate controlled 2- to 5-cm common lambsquarters, common ragweed, and tall morningglory at least 90%; pyrithiobac at the lower rate was the only treatment that failed to control entireleaf and ivyleaf morningglory at least 90%. Bromoxynil and pyrithiobac at either rate controlled 2- to 5-cm sicklepod 33 to 68% whereas glufosinate, glyphosate, and sulfostate controlled ≥99%. Glyphosate and sulfosate applied once or twice controlled hemp sesbania less than 70% and volunteer peanut less than 80%. Bromoxynil and pyrithiobac were the least effective treatments for control of annual grass species and bromoxynil controlled Palmer amaranth less than 80%. Glufosinate controlled broadleaf signalgrass, fall panicum, giant foxtail, green foxtail, large crabgrass, yellow foxtail, seedling johnsongrass, Texas panicum, and glyphosate-resistant corn at least 90% but controlled goosegrass less than 60%. Glyphosate and sulfosate controlled all grass species except glyphosate-resistant corn at least 90%. In greenhouse research, goosegrass could be controlled with glufosinate POST plus a late POST-directed treatment of prometryn plus monosodium salt of methylarsonic acid.

Volatility and drift are problems commonly associated with auxin-like herbicides. Field and greenhouse studies were conducted at Texas A & M University to develop a method of quantifying volatility and subsequent off-target movement of 2,4-D, dicamba, and triclopyr. Rate–response curves were established by applying reduced rates ranging from 4 × 10−1 to 1 × 10−5 times the normal use rates of the herbicides to cotton and soybean and recording injury for 14 d after treatment (DAT) using a rating scale designed to quantify auxin-like herbicide injury. Injury from herbicide volatility was then produced on additional cotton and soybean plants through exposure to vapors of the dimethylamine salt of 2,4-D, diglycolamine salt of dicamba, and butoxyethyl ester of triclopyr using air chambers inside a greenhouse and volatility plots in the field. Injury resulting from this exposure was evaluated for 14 d using the same injury-evaluation scale that was used to produce the rate–response curves. Volatility-injury data were then applied to the rate–response curves so that herbicide rates corresponding with observed injury could be calculated. Using this method, herbicide volatility rates estimated from greenhouse-cotton injury were determined to be 3.0 × 10−3, 1.0 × 10−3, and 4.9 × 10−2 times the use rates of 2,4-D, dicamba, and triclopyr, respectively. Greenhouse-grown soybean developed injury consistent with 1.4 × 10−2, 1.0 × 10−3, and 2.5 × 10−2 times the normal use rate of 2,4-D, dicamba, and triclopyr, respectively. Under field conditions, cotton developed injury symptoms that were consistent with 4.0 × 10−3, 2.0 × 10−3, and 1.25 × 10−1 times the recommended use rates of 2,4-D, dicamba, and triclopyr, respectively. Field soybean displayed injury symptomology concordant with 1.6 × 10−1, 1.0 × 10−2, and 1.1 × 10−1 times the normal use rates of 2,4-D, dicamba, and triclopyr, respectively. This procedure provided herbicide volatility rate estimates that were consistent with rates and injury from the rate–response injury curves. Additional research is needed to ascertain its usefulness in determining long-term effects of drift injury on crop variables such as yield.