Reduced Corn Yield Research Articles

Assessing corn seedbed conditions for emergence

Seedbed temperature and moisture conditions affect crop emergence rate and stand establishment. A 4 × 4 factorial experiment arranged in a split plot design with four replications was conducted for 3 yr at four sites to measure corn emergence rate and stand establishment while monitoring seedbed temperature and soil water content in situ. Four planting dates, beginning as early as the soil could be worked and every 10 d thereafter, were the main plots and four corn (Zea mays L.) hybrids the subplots. Volumetric soil water content in the top 0.10 m was measured a minimum of two times per week using time domain reflectometry (TDR) and estimated daily using a budget model. Measured and estimated soil water contents were similar (R2 = 0.73) and daily estimated values were used in the analysis. Stand establishment for most planting date-site-years ranged from 80 to 99%. Less than 15% of planting date-site-years had stands below 80%, and they were characterized by soil temperatures at or below 12.5°C combined with high soil water contents (>90% available water). Rate of emergence was not associated with stand establishment (P > 0.10) and could not be predicted from soil temperatures below 12.5°C. Results suggest that reduction in stand establishment under conditions of low (12.5°C) soil temperature and high (>field capacity) soil water content may be a factor in corn yield reductions associated with reduced or no tillage. Key words: Time domain reflectometry, soil water content, soil temperature, maize

Weed Control and Corn (Zea mays) Tolerance from Soil-Applied RPA 201772

Field experiments were conducted in 1996, 1997, and 1998 to evaluate weed control and corn tolerance from soil-applied RPA 201772. Treatments alone and in tank mixtures with other corn herbicides were applied preemergence (PRE) at two locations with conventional tillage and at early preplant (EPP) and PRE application timings in no-tillage corn. RPA 201772 was applied alone and in tank mixtures with one-half the typical field rates of other PRE corn herbicides. In conventional tillage experiments in 1996, 1997, and at one location in 1998, all treatments containing RPA 201772 provided > 90% control of common lambsquarters, redroot pigweed, common ragweed, and velvetleaf. In two no-tillage experiments, common lambsquarters and velvetleaf control was > 90%, regardless of application timing. However, control of redroot pigweed and common ragweed varied among years and application timings. Weed control was more variable from herbicide treatments applied EPP compared with the PRE application timing. Giant foxtail control in both tillage systems was rate, timing, and year dependent. RPA 201772 rates higher than 79 g/ha controlled giant foxtail > 85% at three of five locations. At one location, tank mixtures with RPA 201772 increased giant foxtail control. Corn injury occurred in one of two conventional tillage locations and at the no-tillage location in both 1996 and 1997. Injury was most commonly observed in coarse-textured soils with low clay and organic matter and was more severe with higher rates of RPA 201772. Increased corn injury was also observed when RPA 201772 was combined with acetochlor plus dicloramid or BAYFOE 5043 plus metribuzin. Corn injury from RPA 201772 occurred at application rates above the proposed rate for use on corn. In some cases, severe injury to corn reduced corn yield. Injury to corn from RPA 201772 was not unique to any tillage system and was site, year, and rate dependent.

Weed Population and Crop Yield Response to Recommendations from a Weed Control Decision Aid

AbstractSelecting among the diverse options available to manage weeds requires varied knowledge. This study field‐tested the performance of a decision aid model that integrates biological and economic factors to make weed control recommendations. The model was parameterized using data from the literature and subjected to sensitivity analysis. Tactics generated from the resulting model were compared with standard‐herbicide weed control in continuous corn (Zea mays L.) having a long‐term history of various tillage and herbicide application regimes. The model recommended preemergent and postemergent weed control based on weed seed and weed seedling densities, respectively. Using standard‐herbicide weed control resulted in fewer weed seeds in the soil each year compared with model‐based weed control. Variation among model‐based weed control treatments applied to plots with different management histories was eliminated over the course of the study as weed populations shifted in response to weed control practices. The result was a 98% relative abundance of foxtail (Setaria spp.) seedlings after 3 yr of model‐based treatments, compared with 70% in standard‐herbicide treatments. In 1994, the model reduced herbicide use and weed control treatment costs, but often reduced corn yields and net economic returns. In 1995, model‐based treatments maintained or increased corn yields and net returns. In 1996, however, model‐based treatments consistently reduced corn yields and net returns. Variability in control treatment effectiveness and weed‐crop interaction greatly affected the performance of the model. The use of decision‐aid models in weed management is still a developing technology. Interactions of the weed seed bank, weed emergence, treatment effectiveness, weed‐crop interference, and environmental conditions are very complex. The model could become a valuable tool for producers if consistency of weed control were improved by better understanding and modeling of threshold levels and accounting for weed seed production and by adding data on weed emergence, seed production, yield loss, and control efficacy.

Mechanisms of Corn Tolerance and Velvetleaf Suppressive Ability

AbstractCrops that better tolerate weed competition or preempt resources from weeds may reduce dependence on herbicides for weed control and benefit an integrated weed management program. Irrigated field experiments were conducted to identify morphological traits of corn (Zea mays L.) that enhance its tolerance and weed suppressive ability. Two old (circa 1940) and two modern corn hybrids were grown in mixture with five target densities of velvetleaf (Abutilon theophrasti Medik.) in two years. Corn height and leaf area index (LAI) were measured periodically throughout the growing season. Vertical leaf area distribution was measured at corn anthesis. Quantitative estimates of these traits were obtained for each experimental unit using linear and nonlinear regression analysis. Magnitude of the correlation between these trait estimates and corn yield reduction in mixture with velvetleaf or velvetleaf seed capsule production was used as an indicator of the importance of each trait to the enhancement of corn tolerance or velvetleaf suppressive ability. Canopy traits having highest correlation with corn relative yield in 1995 were maximum LAI (r= −0.38) and crop density (r = −0.24). Those with highest correlation in 1996 were crop density (r = ‐0.36), degree days accumulated between emergence and 50% maximum height (r = 0.34) and LAI (r = 0.19), and vertical leaf area distribution (0.49). Corn canopy traits were not correlated with velvetleaf seed production in 1995. However, vertical leaf area distribution (r = 0.60), maximum LAI (r = −0.32), and corn density (r = −0.26) were correlated with velvetleaf seed production in 1996. Results suggest that increasing maximum corn LAI, rate of canopy closure, or height at which leaf area occurs in the canopy can improve corn tolerance and velvetleaf suppressive ability. These traits can be modified by varying cultural practices such as row spacing and population density, or through breeding.

Medic Planting Date Effect on Dry Matter and Nitrogen Accumulation When Clear‐Seeded or Intercropped with Corn

AbstractIntercropping annual forage legumes with row crops has been proposed as a strategy to control erosion, suppress weeds, and contribute biological N to companion or subsequent crops. This experiment evaluated the effect of planting date of two annual medic species [burr and snail medic, Medicago polymorpha L. and M. scutellata (L.) Mill.] on yield and N accumulation of both medic and interseeded corn (Zea mays L.). Medics were either clear‐seeded (i.e., monocropped) or interseeded into corn at five planting dates from 7 May to 13 July in each of two years at East Lansing, MI, on a Capac loam (fine‐loamy, mixed, mesic Aerie Endoaqualf). Clear‐seeded medic produced up to 3 Mg ha−1 of dry matter at 60 d after planting. In the interseeding system, medic dry matter yields were only 50% of yield in a clearseeded system. Average aboveground medic N concentration was 50 and 20 kg ha−1 in clear‐seeded and interseeded systems, respectively. Interseeding at corn planting produced the greatest medic dry matter, but also was associated with the greatest reduction in corn yield. Corn yields were not reduced by interseeding medic 28 d after com planting. Interseeding medic into corn was associated with a positive yield response (3–25%) of subsequent corn grain. Medics reduced fertilizer needs of corn in the subsequent year by 37 kg N ha−1.

Weed Management ofAmaranthusspp. in Corn (Zea mays)

Field experiments were conducted from 1987 to 1990 to investigate the combination of cultural and chemical methods for control ofAmaranthusspp. in corn. The tolerance of corn hybrids to herbicides or herbicide combinations was dependent on application rate. The early season threshold level for a mixed population ofAmaranthusspp. occurred 3.5 wk after emergence. Density ofAmaranthusspp. from 155 to 495 plants/m2caused corn yield reduction of 50%. A quadratic model was derived relating percentage of yield reduction vs. duration of weed competition. The results emphasize the importance of using herbicides, cultural practices, and competition thresholds for an integrated weed control approach ofAmaranthusspp. in corn.

Establishment, Development and Yield of Forage Legumes and Grasses as Cover Crops in Grain Corn in Eastern Canada

AbstractInterseeded cover crops can minimize soil erosion, increase organic matter and nutrient levels and the yield of subsequent crops. However, their performance is very sensitive to local conditions. Field experiments were conducted at two Quebec locations in 1993 and 1994 in order to evaluate the potential use of forage legumes and grasses as interseeds in corn in eastern Canada. Twelve forage species were evaluated. Fall rye (Secale cereal L.), hairy vetch (Vicia villosa Roth), a mixture of red clover (Trifolium pratense L.) and ryegrass (Lolium multiflorum Lam), a mixture of white clover (Trifolium repens L.) and ryegrass, subterranean clover (Trifolium subterraneum L.), yellow sweet clover (Melilotus officinalis Lam.), black medic (Medicago lupulina L.), Persian clover (Trifolium resupinatum L.), strawberry clover (Trifolium fragiferum L.), crimson clover (Trifolium incarnatum L.), annual alfalfa (Medicago saliva L.) and berseem clover (Trifolium alexandrinum L.) were seeded at two planting dates (10 and 20 days after corn emergence). The control treatments were: hand weeding, chemical weeding and non‐weeded. Early seeded forages established better and had higher biomass accumulation than the late seeded ones. In the presence of larger weed populations, the interseeded forages did not develop well due to competition with the weeds. At Macdonald crimson clover provided good soil cover while Persian clover, fall rye and alfalfa provided relatively little cover. Strawberry clover and hairy vetch did not provide early ground cover due to their late development. Forage mixtures of red or white clover and rye grass established well and achieved high populations at the end of the growing season. Fall rye provided good early ground cover but senesced by the middle of the season. The better establishment and early germination of crimson clover caused a 19% reduction in corn grain yield in 1993. In 1994 none of the cover crops caused a reduction in corn yield.

Wheat residue management options for no-till corn

Corn (Zea mays L.) yield reduction following winter wheat (Triticum aestivum L.) in no-till systems prompted a study on the effects of tillage and residue management systems on corn growth and seedbed conditions. Four methods for managing wheat residue (all residue removed, straw baled after harvest, straw left on the soil surface, straw left on the soil surface plus application of 50 kg ha−1N in the fall) were evaluated at two tillage levels: fall moldboard plow (MP) and no-till (NT). No-till treatments required at least 2 more days to achieve 50% corn emergence and 50% silking, and had the lowest corn biomass at 5 and 7 wk after planting. Grain yield was similar among MP treatments and averaged 1.1 t ha−1 higher than NT treatments (P < 0.05). Completely removing all wheat residue from NT plots reduced the number of days required to achieve 50% corn emergence and increased grain yields by 0.43 and 0.61 t ha–1 over baling and not baling straw, respectively, but still resulted in 8% lower grain yields than MP treatments. Grain yield differences among MP treatments were insignificant regardless of the amount of wheat residue left on the surface or N application in the fall. Early in the growing season, the NT treatments where residue was not removed had lower soil growing degree days (soil GDD) compared with MP (baled) treatment, and higher soil moisture levels in the top 15 cm compared with all other treatments. The application of 50 kg N ha−1 in the fall to NT (not baled) plots influenced neither the amount of wheat residue on the soil surface, nor the soil NO3-N levels at planting. Our results suggest that corn response in NT systems after wheat mostly depends on residue level. Key words: Winter wheat, straw management, no-till, corn, soil temperature, soil moisture

Corn Yield is Equal in Conventional, Reduced, and No Tillage after 20 Years

AbstractReduced tillage has increased dramatically over the past several years and is expected to continue to increase in the future. Continuous no‐till may become a popular tillage system with growers to facilitate compliance with government programs to control soil erosion. The objective of this research was to evaluate the long‐term effects of four tillage systems and five fertilizer regimes on corn (Zea mays L.) yield. A 20‐yr continuous‐corn tillage ✕ fertility study was conducted from 1970 to 1990 on an Ebbert silt loam (fine‐silty, mixed, mesic Argiaquic Argialbolls), an imperfectly drained soil at the Belleville Research Center, Belleville, IL. Starter fertilizer did not increase corn height within a tillage system. Height was greater in no‐till compared with conventional till (moldboard plow), reduced till (chisel plow), or alternate till (2 yr no‐till, 1 yr moldboard plow) with or without a starter fertilizer. There was no difference in population among tillage systems due to fertilizer treatment. Corn population was lower in no‐till compared with conventional till regardless of fertilizer treatment. Starter fertilizer did not increase yield in any tillage system. Corn yield averaged 5 to 7% lower in no‐till compared with conventional till or reduced till where a starter fertilizer was applied. There was no difference in yield among tillage systems when NPK was broadcast. Corn yield was equal in conventional till, alternate till, reduced till, and no‐till with fertilizer applied broadcast on an imperfectly drained soil. Continuous no‐till with an imperfectly drained soil does not reduce corn yield.

Velvetleaf (Abutilon theophrasti) Effect on Corn (Zea mays) Growth and Yield in South Dakota

Studies were conducted at two sites in South Dakota in 1992 and at one site in 1993 to measure the effect of velvetleaf on corn growth and yield. Velvetleaf was overseeded in corn rows and thinned to densities of 0, 1.3, 4, 12, and 24 plants/m2. Velvetleaf leaf area index and total biomass were positively correlated with velvetleaf density. Biomass per velvetleaf plant and corn biomass were correlated negatively with velvetleaf density. The percent corn yield reduction was similar for locations and years in spite of large yield differences. Maximum yield loss estimated by a hyperbolic yield reduction model was 37.2% with a loss of 4.4% per unit velvetleaf density.

Effect of Nicosulfuron on Johnsongrass (Sorghum halepense) Control and Corn (Zea mays) Performance

Field experiments were conducted at two locations in North Carolina during the summer of 1992 to ascertain the reasons for stunted growth of corn noticed occasionally in fields treated POST with nicosulfuron to control dense infestations of johnsongrass. Treatments consisted of nicosulfuron at 35 g ai/ha sprayed POST, either over-top or post-directed only to johnsongrass in a single early application or in sequential applications of 17.5 g/ha. Checks included a hand-weeded, paraquat post-directed to johnsongrass, and non-weeded. Nicosulfuron provided satisfactory control of johnsongrass irrespective of whether applied once or sequentially. Corn yield in nicosulfuron-treated plots was as much as three times greater than in non-treated plots depending on hybrid and location. In the absence of johnsongrass interference, nicosulfuron caused a corn yield reduction of 6 to 9%. However, in the presence of johnsongrass interference, an additional 16 to 26% reduction in yield occurred with a POST application of nicosulfuron. Reductions in corn plant height and dry matter accumulation also were noticed for nicosulfuron treatments compared to post-directed application of paraquat and hand removal of johnsongrass.

Influence of Weed Density and Distribution on Corn (Zea mays) Yield

The impact of weed density and weed distribution on irrigated corn yield was investigated in Colorado. Weed densities examined were 0,33,50, or 100% of the indigenous weed population. A series of weed distribution treatments were achieved by varying the length of the weed-free and weedy zones within the corn row while maintaining a constant weed population of 33 or 50% of the indigenous weed level. Grain yield was affected by weed density, but not by weed distribution. Each additional weed reduced corn yield 8.5 and 2.3 kg ha−1in 1991 and 1992, respectively. When corn yields were estimated with a computer weed/corn management model, weed densities 5 to 8 wk after planting provided a better yield reduction estimate than weed densities immediately before harvest.

Velvetleaf (Abutilon theophrasti) Competition and Economic Thresholds in Conventional- and No-Tillage Corn (Zea mays)

Studies were conducted in conventional and no-tillage corn in 1990, 1991, and 1992 at Wooster, OH, to measure corn yield and velvetleaf seed production in response to density of early and late emerging velvetleaf, and to estimate economic thresholds. The percent reduction in corn yield fit a hyperbolic function over velvetleaf densities from 1 to 30 plants m2. The percent yield loss and velvetleaf seed production were higher in a warm, wet year (1990) than in a dry (1991) or cold, wet year (1992). The percent corn yield reduction was generally greater in no-tillage than in conventional tillage and from early rather than late emerging velvetleaf. Maximum velvetleaf seed production ranged from about 18,000 seeds m2for early emerging weeds in no-tillage in 1990 to 100 seeds m2for late emerging weeds in no-tillage in 1992. The single year economic threshold for early emerging velvetleaf ranged from 0.40 to 14.0 velvetleaf m2in conventional tillage and 0.13 to 3.13 in no-tillage. Economic thresholds that were predicted using yield goal information deviated from actual thresholds (using actual yields) for a given year by −43 to 30%. Single year economic thresholds were similar in both tillage treatments, but their value for management decisions is questionable due to variation among growing seasons and weed seed production from subthreshold populations.

Cover Crop and Nitrogen Fertility Effects on Southern Corn Rootworm (Coleoptera: Chrysomelidae) Damage in Corn

The effect of winter legume and grass cover crops, nitrogen fertility, and insecticide use on seedling injury by the southern corn rootworm, Diabrotica undecimpunctata howardi Barber, was investigated in no-tillage field corn, Zea mays L. Rootworm injury was most severe following hairy vetch, Vicia villosa Roth, and least severe following no cover crop (fallow). Injury after wheat, Triticum aestivum L.; rye, Secale cereale L.; or crimson clover, Trifolium incarnatum L., was intermediate compared with injury after vetch and fallow. Rootworm injury following vetch reduced corn stand by ≥50% compared with fallow in all years. Corn plant stand was not different between cover-crop treatments when terbufos insecticide was applied at planting, indicating that cover-crop treatments did not affect corn stand establishment directly. Despite reductions in plant population, remaining plants compensated by producing more ears and grain weight per plant, which resulted in little reduction in corn yield in all cover-crop treatments except after vetch. Nitrogen fertility did not affect stand loss and plant injury by the southern com rootworm, and corn yield response to nitrogen fertility was not affected by rootworm control with a soil insecticide. Use of legume cover crops, especially hairy vetch, to prevent soil erosion over the winter and provide a source of nitrogen may enhance the pest status of the southern com rootworm in no-tillage com production in the southeastern United States.

Interference of Redroot Pigweed (Amaranthus retroflexus) in Corn (Zea mays)

Redroot pigweed is a major weed in corn throughout Ontario. Field experiments were conducted at two locations in 1991 and 1992 to determine the influence of selected densities and emergence times of redroot pigweed on corn growth and grain yield. Redroot pigweed densities of 0.5, 1, 2, 4 and 8 plants per m of row were established within 12.5 cm on either side of the corn row. In both years, redroot pigweed seeds were planted concurrently and with corn at the 3- to 5-leaf stage of corn growth. A density of 0.5 redroot pigweed per m of row from the first (earlier) emergence date of pigweed (in most cases, up to the 4-leaf stage of corn) or four redroot pigweed per m of row from the second (later) emergence date of pigweed (in most cases, between the 4- and 7-leaf stage of corn) reduced corn yield by 5%. Redroot pigweed emerging after the 7-leaf stage of corn growth did not reduce yield. Redroot pigweed seed production was dependent upon its density and time of emergence. The time of redroot pigweed emergence, relative to corn, may be more important than its density in assessing the need for postemergence control.

Soil Insecticide and Placement Influence Corn (Zea mays) Tolerance to Nicosulfuron

Field experiments were conducted in 1991 and 1992 to evaluate corn tolerance to nicosulfuron following in-furrow or surface-band applications of seven soil-applied insecticides. The organophosphate insecticides evaluated included terbufos (15G and 20CR formulations), phorate, chlorpyrifos, fonofos, and DPX-43898, as well as the synthetic pyrethroid tefluthrin. Potential for a nicosulfuron/ insecticide interaction to injure corn was ranked as follows: terbufos 15G = phorate > terbufos 20CR > fonofos. Chlorpyrifos, DPX-43898, or tefluthrin followed by nicosulfuron caused no significant corn injury. Corn injury and yield reduction were greater in corn treated in-furrow compared with surface-band. Soil moisture at nicosulfuron application was more influential in causing corn injury and loss of yield than growth stage of corn at nicosulfuron application.

Soybean (Glycine max) and Rotational Crop Response to PPI Chlorimuron, Clomazone, Imazaquin, and Imazethapyr

Field studies were conducted from 1989 to 1992 to evaluate soybean and rotational crop tolerance to PPI applications of chlorimuron (23 to 140 g ai/ha), clomazone (560 to 3360 g/ha), imazaquin (70 to 420 g/ha), and imazethapyr (53 to 310 g/ha). Soybean injury was evident only in 1989. Soybean height reduction 45 d after application increased linearly with increasing rates of chlorimuron, imazaquin, and imazethapyr. Chlorimuron at 140 g/ha and imazaquin at 420 g/ha reduced soybean height 120 d after planting. None of the herbicides influenced soybean density. Chlorimuron and imazaquin reduced soybean seed yield linearly as rates increased. None of the herbicides reduced subsequent wheat yield. Corn height reduction increased as the rate of imazaquin and imazethapyr increased. Imazethapyr and imazaquin caused 2 to 40% and 1 to 12% height reduction at 30 d after planting, respectively. Imazethapyr at 310 g/ha applied the previous year reduced corn height at 120 d after planting. There were no differences in corn density. Imazaquin and imazethapyr at 420 and 310 g/ha, respectively, applied the previous year reduced corn yield.

Reduced-Herbicide Weed Management Systems for No-Tillage Corn (Zea mays) in a Hairy Vetch (Vicia villosa) Cover Crop

Weed management treatments with various degrees of herbicide inputs were applied with or without a hairy vetch cover crop to no-tillage corn in four field experiments at Beltsville, MD. A hairy vetch living mulch in the no-treatment control or a dead mulch in the mowed treatment improved weed control during the first 6 wk of the season but weed control deteriorated in these treatments thereafter. Competition from weeds and/or uncontrolled vetch in these treatments without herbicides reduced corn yield in three of four years by an average of 46% compared with a standard PRE herbicide treatment of 0.6 kg ai/ha of paraquat plus 1.1 kg ai/ha of atrazine plus 2.2 kg ai/ha of metolachlor. Reducing atrazine and metolachlor to one-fourth the rate of the standard treatment in the absence of cover crop reduced weed control in three of four years and corn yield in two of four years compared with the standard treatment. Hairy vetch had little influence on weed control or corn yield with any herbicide treatments.

Modeling the Influence of Postdirected Sethoxydim on Corn Yields

AbstractPostdirected sethoxydim 2‐[1‐(ethoxyimino)butyl]‐5‐[2‐(ethylthio) propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one, used to control monocot weeds, is known to reduce corn (Zea mays L.) yields. The objective was to develop an integrative model combining a growing plant with the effect of sethoxydim. CERES‐Maize (version 1.0) was modified to respond to herbicide‐induced grain yield reductions by incorporating a herbicide stress factor and the stress duration into calculation of the daily biomass production. Herbicide stress was defined as the difference in net photosynthesis between treated and nontreated plants. A seasonal herbicide stress factor (0–1) was determined from field measurements of treated and nontreated corn yields as a function of sethoxydim concentration (110 and 220 g a.i. ha−1) for all application dates. This factor was modified to reflect the period of the herbicide stress duration by scaling it to the fraction of time the sethoxydim was active. Field experiments were conducted using four corn hybrids (Pioneer 3475, 3379, 3377, and 3183). Data from 1988 field experiments were used to calibrate the genetic inputs for each hybrid and develop a herbicide stress relationship. The data collected in 1989 were used to validate the modifications made to CERES‐Maize. Overall, the model predicted that sethoxydim use would reduce corn yields, and this trend was consistent with independently measured field data. Based on the ratio of treated to nontreated yields for simulations and measurements, the model predictions underestimated the sethoxydim effect for the hybrids 3475, 3379, and 3183.

Soybean (Glycine max) Herbicide Carryover to Grain and Fiber Crops

Experiments were conducted in 1988, 1989, and 1990 at two locations in Missouri to study the influence of fall tillage on the soil persistence of several soybean herbicides and subsequent injury to the rotational crops winter wheat, corn, cotton, and grain sorghum. Chlorimuron, clomazone, imazaquin, imazethapyr, and metribuzin plus chlorimuron were applied at their label and double label rate (2X) in soybean. Fall chisel plowing did not influence the carryover potential of these herbicides on any of the crops, in any year, or at either location of the research. However, herbicides injured several of these rotational crops. The 2X-label rate of clomazone reduced winter wheat grain yield at both locations. None of the herbicide treatments at either location reduced corn yield. Imazaquin applied at the 2X rate caused greater than 30% visible injury to cotton in 1989; however, cotton yield was not affected. The 2X rate of chlorimuron caused a reduction of grain sorghum yield in 1989, but not in 1990 or 1991 at Novelty.