Field experiments were conducted at Wooster, OH, in 2010 and 2011 to evaluate the effect of simulated drift rates of 2,4-D, dicamba, and 2,4-D plus glyphosate on processing broccoli and bell pepper. Treatments were made in July of each year when bell pepper and broccoli were at the 10- and eight-leaf stage, respectively, and included five 2,4-D rates (1/50, 1/100, 1/150, 1/200, and 1/400 of the recommended field rate of 840 g ae ha−1), five dicamba rates (1/50, 1/100, 1/150, 1/200, and 1/400 of the recommended field rate of 560 g ae ha−1), and three rates of 2,4-D plus glyphosate (1/100, 1/200, and 1/400 of the recommended field rates). Crop injury was recorded at 7 and 28 d after treatment (DAT). Broccoli and bell pepper responded differently to simulated drift rates each year with higher initial injury ratings observed in 2010, and more persistent symptoms in 2011. 2,4-D at the 1/50 rate reduced broccoli yield by approximately 50% in 2010. Simulated drift rates of 2,4-D did not cause broccoli yield reduction in 2011, nor did simulated drift rates of dicamba, or 2,4-D plus glyphosate reduce yield either year. Although simulated drift treatments did not reduce total yield of bell pepper, the timing of fruit maturity was affected. Yield at first harvest was reduced by high simulated drift rates of each herbicide and by the herbicide tank mix. These results indicate that broccoli and bell pepper are sensitive to very low doses of 2,4-D and dicamba that are typical of those encountered in drift events. The impact of actual drift on delayed maturity and total yield of these crops is likely to be costly for the farmer.

Producers in the semiarid Great Plains are seeking management strategies to delay development of herbicide resistance. The objective of this study was to determine if cultural systems could control weeds in proso millet (Panicum miliaceum), thus eliminating the need for herbicides and removing selection pressure. Initially, we evaluated individual cultural practices for improving competitiveness of proso millet. Increasing seeding rate, banding N fertilizer with the seeds, growing a taller cultivar, and eliminating tillage favored proso millet over redroot pigweed (Amaranthus retroflexus). Combining several cultural practices with delayed planting in a cultural system reduced biomass and seed production of two pigweed species 85% or more in both tilled and no-till systems, subsequently eliminating proso millet yield loss. Density of the two pigweed species was sevenfold greater in the tilled system, yet the cultural system approach was still effective. Cultural system impact on seed production suggests that pigweed densities will not increase over time. With cultural systems, producers can minimize selection pressure, thus delaying development of herbicide resistance.

The selection of herbicide-resistant weeds in grain sorghum production has prompted researchers to explore alternative herbicides to prevent, delay, and manage herbicide-resistant weed biotypes. Greenhouse and field experiments were conducted to evaluate the differential response of sorghum hybrids to POST application of mesotrione. In a greenhouse experiment, 85 sorghum hybrids were treated with 0, 52, 105, 210, and 315 g ai/ha mesotrione when plants were at the three- to four-leaf collar stage. Sorghum response ranged from susceptible to tolerant sorghum hybrids. ‘Pioneer 84G62’, ‘Pioneer 85G01’, and ‘Triumph TR 438’ were the three most susceptible, whereas ‘Dekalb DKS35-70’, ‘Frontier F222E’, and ‘Asgrow Seneca’ were the three most tolerant hybrids. One week after treatment (WAT), the mesotrione rate causing 50% visible injury ranged from 121 to 184 and 64 to 91 g/ha in the most tolerant and susceptible hybrids, respectively. Mesotrione dose–response studies were conducted under field conditions on four sorghum hybrids. One WAT, injury symptoms were greater (up to 23%) in Pioneer 85G01 than in Asgrow Seneca (< 14%). However, all plants appeared normal by the end of the growing season. In addition, sorghum yields were not reduced by mesotrione treatments as verified by correlation coefficient analysis.

Yellow nutsedge can readily puncture the plastic mulch used in plasticulture tomato production, compromising the benefits of the mulch and hastening its deterioration. Our objective was to identify a PRE-applied (i.e., under the plastic) treatment to minimize yellow nutsedge puncturing. In a greenhouse study a series of halosulfuron rates were PRE-applied to soil planted with yellow nutsedge tubers. These rates were also applied to established plants but with selective spray contact. Nonlinear regression revealed that the concentration of halosulfuron required to reduce dry weights by 90% (GR90) for PRE-applied halosulfuron was 11.6 g/ha. The GR90 for POST-applied halosulfuron was 17.1, 28.1, and 11.6 g/ha for foliar-only, soil-only and foliar plus soil spray contact, respectively. Thus halosulfuron was more effective as a POST-applied, foliar-contacting treatment. However, soil activity was deemed likely sufficient to suppress plastic puncturing. In a noncrop field study, suppression of puncturing was influenced (P < 0.05) by the rate of both PRE-applied halosulfuron and S-metolachlor. A field study with tomato was conducted to evaluate six selective treatments using plastic mulch, PRE-applied S-metolachlor, and the combination of PRE or PRE/POST-split applications of halosulfuron. Plastic alone increased tomato yield threefold compared with bare ground. The addition of various herbicide programs neither increased nor reduced yield compared with plastic alone. Selected herbicide treatments did reduce mulch puncturing but not to the extent or duration that would allow sequential crops to receive the full benefit of nonpunctured plastic.

Purple loosestrife is an invasive, introduced plant that is usually associated with wetland, marshy, or riparian sites. It is found across the northern tier states and provinces in North America. Purple loosestrife affects the diversity of native wetland ecosystems. Infestations lead to severe wildlife habitat degradation, loss of species diversity, and displacement of wildlife-supporting native vegetation, such as cattails and bulrushes. The plant spreads effectively along waterways, and the thick, matted root system can rapidly clog irrigation ditches, resulting in decreased water flow and increased maintenance. Effective management of purple loosestrife along waterways and in riparian areas requires integrating management strategies to prevent further introductions, detecting and eradicating new infestations, and containing and controlling large-scale infestations. Management practices that aid in the control of purple loosestrife include herbicide, physical, and biological practices. Each infestation site should be individually evaluated to determine the appropriate control measure. Factors to be considered include the proximity and type of vegetation on the site, whether the water is flowing or still, and the utilization of the site and the water (domestic, irrigation, recreation, or scenic value).

Studies were conducted in 2010 and 2011 to determine the effect of herbicide-based Palmer amaranth management systems in ‘Covington' sweetpotato. Treatments consisted of three herbicide application times. Pretransplant applications were flumioxazin at 107 g ai ha−1, fomesafen at 280 g ai ha−1, flumioxazin at 70 g ha−1 plus pyroxasulfone at 89 g ai ha−1, or no herbicide. A second herbicide application was applied within 1 d after transplanting (DAP) and consisted of S-metolachlor at 800 g ai ha−1, clomazone at 630 g ai ha−1, or no herbicide. Two weeks after planting (WAP) plots received S-metolachlor at 800 g ha−1, metribuzin at 140 g ai ha−1, a tank mix of S-metolachlor at 800 g ha−1 plus metribuzin at 140 g ha−1, hand-weeding followed by (fb) S-metolachlor at 800 g ha−1, or no herbicide. Crop tolerance, Palmer amaranth control, and sweetpotato yield in systems containing fomesafen pretransplant were similar to flumioxazin-containing systems. Systems containing flumioxazin plus pyroxasulfone pretransplant resulted in increased crop stunting and decreased sweetpotato yield in 2010, compared with systems containing flumioxazin or fomesafen, but were similar to systems with flumioxazin or fomesafen in 2011. In 2010, systems containing S-metolachlor applied within 1 DAP resulted in increased sweetpotato injury, similar Palmer amaranth control, and reduced no. 1, jumbo, and total sweetpotato yield, compared with systems with clomazone. In 2011, systems containing clomazone were more injurious to sweetpotato than systems receiving S-metolachlor, but Palmer amaranth control and sweetpotato yield were similar. Systems containing metribuzin 2 WAP resulted in increased sweetpotato injury and Palmer amaranth control (in 2010) but similar no. 1 and total sweetpotato yields, compared with systems containing S-metolachlor at 2 WAP. Hand-weeding fb S-metolachlor provided greater Palmer amaranth control and no. 1 sweetpotato yield than did systems of S-metolachlor without a preceding hand-weeding event in 2010.

Experiments were conducted to determine the inheritance of resistance in crosses between imazethapyr-resistant rice and red rice. Past experiments on red rice control, using the Clearfield rice technology, resulted in outcrossing between Clearfield rice and Stuttgart strawhull red rice. The F2 generation of these spontaneous crosses were characterized with respect to inheritance of imazethapyr resistance, leaf color and leaf pubescence, and seed shattering, pubescence, color, and size. Agronomic traits of hybrids were also observed in relation to their parents. To determine the segregation of resistance among F2 phenotypes, the response of three- to four-leaf plants to imazethapyr was scored 3 wk after application as resistant (R, no imazethapyr symptoms), susceptible (S, death of plants), or intermediate (I, stunted plants). R, I, and S phenotypes segregated in a 1:2:1 ratio in the F2 generation. Two- or three-gene inheritance was documented for leaf and seed characteristics. A wide range in onset of flowering (70 to 130 d after planting) was observed in F2 families, although 6% of the plants did not flower during the growing season. F2 plants were taller and had more tillers than any of their parents. Resistance to imazethapyr is associated with a single, incompletely dominant allele.

Seven annual weed species were treated under greenhouse conditions with six rates of either nicosulfuron, rimsulfuron, or a 1:1 mixture (DPX-79406). Herbicide rates in g ai/ha producing 90% dry biomass reduction (GR90) were calculated for each weed species. Accordingly, weeds were classified as very susceptible when GR90 ≤ 9, susceptible when 9 < GR90 ≤ 18, moderately susceptible when 18 < GR90 ≤ 27, and tolerant when, GR90 > 27. Giant and green foxtails were very susceptible to the three herbicides. Proso millet was very susceptible to rimsulfuron and DPX-79406, and susceptible to nicosulfuron. Wild oat was susceptible to nicosulfuron and DPX-79406, and moderately susceptible to rimsulfuron. Redroot pigweed was very susceptible to nicosulfuron; whereas, it was susceptible to rimsulfuron and DPX-79406. Common ragweed and smooth crabgrass were tolerant to the three herbicides. In a second experiment, we used regression estimate analysis with an additive reference model to evaluate nicosulfuron and rimsulfuron interaction on corn, soybean, common ragweed, and smooth crabgrass. We found these herbicides synergistic on smooth crabgrass, antagonistic on soybean, less than additive on common ragweed, and additive on corn.

Dense populations of glyphosate-resistant (GR) Italian ryegrass are problematic for spring burndown herbicide programs and crop establishment in the midsouthern United States. Two field studies were conducted to evaluate fall-applied residual herbicides for control of GR Italian ryegrass and to identify the most effective application timing for these herbicides. Fall applications of clomazone at 0.84 and 1.12 kg ai ha−1, pyroxasulfone at 0.16 kg ai ha−1, and S-metolachlor at 1.79 kg ai ha−1 controlled GR Italian ryegrass ≥ 93% 180 d after application. Control from incorporated applications of pendimethalin at 1.59 kg ai ha−1 and trifluralin at 1.68 kg ai ha−1 and surface applications of S-metolachlor at 1.42 kg ha−1 provided control similar to the best treatments. Glyphosate-resistant Italian ryegrass control following clomazone, pyroxasulfone, S-metolachlor, or trifluralin applied in mid September, October, or November exceeded that from fall tillage by 19 to 56% at 90 and 140 d after the last treatment. Pyroxasulfone and S-metolachlor controlled more GR Italian ryegrass following October or November applications compared with those in September at both 90 and 140 d after the last application timing. However, the benefit of delaying clomazone application from October to November was not realized until the last evaluation (140 d after the last treatment). Clomazone, pyroxasulfone, and S-metolachlor offer growers the best opportunity for residual control of GR Italian ryegrass, and control is optimized when these herbicides are applied in November.

Rates and application timings of postemergence herbicides for wild oat control in spring wheat and barley were evaluated at Crookston, MN, from 1994 to 1996. Diclofop, imazamethabenz, and fenoxaprop plus MCPA plus thifensulfuron plus tribenuron were applied to one- to three-leaf wild oat; and difenzoquat, imazamethabenz, fenoxaprop plus MCPA plus thifensulfuron plus tribenuron, and fenoxaprop plus 2,4-D plus MCPA were applied to four- to five-leaf wild oat at 1/2 ×, 3/4 ×, and 1 × rates. Wild oat response to herbicide rate and timing was similar in wheat and barley. Wild oat control with 1/2 × rates generally was less than that with 3/4 × rates, which was lower than or similar to that with 1 × rates. Wild oat biomass was often reduced less with 1/2 × rates than 1 × rates. However, reducing herbicide rates generally did not influence grain yields or net economic return. Grain yields and net economic return were generally greater in herbicide-treated plots than in the nontreated control.

Widespread groundwater contamination has prompted studies on the fate and transport of solute through soil. Large quantities of atrazine and metribuzin are applied annually in the Humid Pampas of Argentina, creating the need to study the fate of these herbicides in soils of the region. The objective of this work was to study the vertical transport of atrazine and metribuzin in packed soil columns for three loam soils representative of the Humid Pampas of Argentina. Bromide was used as a nonreactive tracer. The convection dispersion equation was fitted to chemical breakthrough data to obtain a parameter characterizing chemical transport. Bromide breakthrough curves (BTCs) were similar among soils. BTCs for atrazine and metribuzin revealed significant interaction among soils and herbicides. The average values for the organic carbon (OC) partition coefficients (Koc) derived from column flow experiments were 119 and 48 ml/g for atrazine and metribuzin, respectively. Metribuzin in leachate was 97.3% of the total recovered, whereas atrazine was 3.5%. This behavior can be explained by their different affinities to OC. The OC contents of the Balcarce, Necochea, and Nueve de Julio soils were 4.1, 3.4, and 1.9%, respectively. The lowest leaching values of herbicides were found in the Balcarce soil, suggesting that OC content was the main factor in controlling herbicide transport in these soils.

Some herbicides applied to corn or soybean can carry over and injure vegetable crops grown the following year. Injury and yield effects on vegetable crops from carryover of nicosulfuron and flumetsulam 1 yr after application to corn and from carryover of imazethapyr and imazamox 1 yr after application to soybean were evaluated. Experiments were conducted at Oakes, ND, on sandy loam soils with pH 7.7 in 1994 and pH 7.3 in 1996. Nicosulfuron and flumetsulam were applied to corn, and imazethapyr was applied to soybean at a standard herbicide rate (1×) (35, 56, and 70 g ai/ha, respectively) or 2× rates in 1994 and at 1×, 2×, or 4× rates in 1996. Imazamox was also applied to soybean at 1× (35 g ai/ha), 2×, or 4× rates in 1996. Cabbage, carrot, potato, onion, acorn squash, and tomato were planted in 1995, 1997, and 1998. In 1995, residual imazethapyr delayed tomato maturity but did not reduce tomato yield. Other vegetable crops were not injured by herbicide residues. In 1997, flumetsulam carryover injured plants and reduced yields of cabbage and squash; nicosulfuron carryover injured cabbage and onion plants and reduced onion yield; and imazethapyr carryover injured cabbage, onion, and tomato plants and reduced tomato yield. Most crop injury occurred only at the 2× or 4× herbicide rates. Potato and carrot were not injured by herbicide carryover. Herbicides applied to corn or soybean in 1996 did not carry over to injure any vegetable planted in 1998. The low rate of injury to vegetable crops in this study was mostly due to adequate soil moisture and warm summer soil temperatures, which enhanced microbial degradation of these herbicides and hastened their dissipation. Low clay and moderately low soil organic matter, and slightly alkaline soil pH, also promoted dissipation of some herbicides.

Field studies were conducted from 1988 to 1990 on a Sharkey clay to evaluate residual weed control in rice with quinclorac applied PPI, PRE to dry soil, and PRE to moist soil. Quinclorac applied at 0.4 or 0.6 kg ai ha−1 PPI or PRE to dry or moist soil controlled more than 80% of barnyardgrass, pitted morningglory, and hemp sesbania without rice injury. Quinclorac applied at 0.3 kg ha−1 controlled these three weed species substantially but inconsistently. No rice injury was observed from any quinclorac treatment. Except for one of three years when irrigation was delayed for 7 d after PRE application to dry soil, application timing did not consistently affect weed control or rice yield.

The efficacy of reduced rates of fomesafen, bentazon plus acifluorfen, and chlorimuron, in combination with sethoxydim was investigated in New Jersey from 1989 to 1991. Herbicides applied at sequential 0.25x rates controlled common lambsquarters, common ragweed, and stinkgrass. Chlorimuron plus sethoxydim did not control common lambsquarters at any rate. Generally, herbicides applied at 0.5x rates were not as effective as the full or sequential 0.25x rates. Yields of plots treated with reduced rates were equal to or greater than those treated with full rates.

Giant ragweed is one of the most competitive annual broadleaf weeds in soybean production fields in the midwestern United States and eastern Canada because of its early emergence, rapid growth rate, high plasticity, and resistance to glyphosate and acetolactate synthase inhibitors. Therefore, early-season management of giant ragweed is critical to avoid yield loss. The objectives of this study were to evaluate control of glyphosate-resistant giant ragweed through the integration of preplant tillage or 2,4-D; PRE or early POST (EPOST) followed by (fb) late POST (LPOST) herbicide programs with or without preplant tillage or 2,4-D; and their effect on soybean injury and yield. A field study was conducted in 2013 and 2014 in David City, NE in a field infested with glyphosate-resistant giant ragweed. Preplant tillage or 2,4-D application provided > 90% control of glyphosate-resistant giant ragweed 14 d after preplant treatment. Giant ragweed control and biomass reduction were consistently > 90% with preplant tillage or 2,4-D fb sulfentrazone plus cloransulam PRE or glyphosate plus cloransulam EPOST fb glyphosate plus fomesafen or lactofen LPOST compared with ≤ 86% control with same treatments without preplant tillage or 2,4-D. PRE or EPOST fb LPOST herbicide programs preceded by preplant treatments resulted in giant ragweed density < 2 plants m−2 and soybean yield > 2,400 kg ha−1 compared with the density of ≥ 2 plants m−2 and soybean yield < 1,800 kg ha−1 under PRE or EPOST fb LPOST herbicide programs. The contrast analysis also indicated that preplant tillage or 2,4-D fb a PRE or POST program was more effective for giant ragweed management compared with PRE fb POST herbicide programs. Integration of preplant tillage would provide an alternative method for early-season control of giant ragweed; however, a follow up application of herbicides is needed for season-long control in soybean.

There is little information on the tolerance of leguminous crops to saflufenacil. A field study was conducted three times over a 2-yr period (2006, 2007) in Ontario, Canada, to determine the tolerance of adzuki bean, cranberry bean, lima bean, processing pea, snap bean, soybean, and white (navy) bean to saflufenacil applied PRE at 100 and 200 g ai/ha. Saflufenacil caused 51 to 99% injury, reduced height 25 to 93%, reduced shoot dry weight 92 to 99%, and reduced seed yield 56 to 99% in adzuki bean, cranberry bean, lima bean, snap bean, and white bean. Injury was lower in soybean and processing pea. Saflufenacil caused 1 to 25% injury, reduced height 3 to 13%, reduced shoot dry weight 5 to 30%, and reduced seed yield 0 to 4% in soybean and processing pea. Cranberry bean, snap bean, white bean, and lima bean were the most sensitive crops to saflufenacil followed by adzuki bean. Soybean and processing pea were the most tolerant to saflufenacil. Based on these results, saflufenacil applied PRE can be safely used in specific cultivars of pea and soybean at the proposed rate of 100 g/ha. However, there is not an acceptable margin of crop safety for saflufenacil PRE at 100 or 200 g/ha in adzuki, cranberry, lima, snap, and white bean.

Broomrapes (Orobanche spp.) are root holoparasitic plants that cause severe damage to economically important crops, especially in Mediterranean countries. Egyptian broomrape is the most troublesome weed on tomatoes grown for processing in Israel. In the present study, we tested the efficacy and selectivity of four sulfonylurea herbicides in controlling Egyptian broomrape on tomatoes grown in pots under greenhouse conditions. MON 37500, rimsulfuron, HOE 404 and SL-160 were applied postemergence (POST) and preplant incorporated (PPI) followed by POST applications. MON 37500 and rimsulfuron were more selective to tomato and controlled the parasite more effectively than HOE 404 and SL-160. MON 37500 and rimsulfuron at 50 and 100 g ai/ha and at 100, 150, and 200 g ai/ha, respectively, applied on tomato foliage 14, 28, and 42 d after planting (DAP) and followed by sprinkler irrigation to field capacity, resulted in complete control of the parasite. However, a significant reduction in control efficacy was observed when the experiment was repeated with charcoal-topped pots, suggesting that the herbicides act mainly through the soil. Except for rimsulfuron, the PPI followed by two POST treatments was more phytotoxic to tomato plants than the POST treatments. The PPI plus POST applications controlled Egyptian broomrape effectively, but tomato plants were injured by HOE 404 at all PPI application rates and by MON 37500 at the high rate at 150 g/ha. The present study determined that three POST applications or a PPI application followed by two POST applications of MON 37500 at 50 or 100 g/ha, or rimsulfuron at 100, 150, or 200 g/ha were effective and selective in controlling Egyptian broomrape on tomato, under greenhouse conditions.

Glyphosate-resistant (GR) weeds have been a prime challenge to the sustainability of GR cotton-based production systems of the midsouthern United States. Barnyardgrass is known to be a high-risk species for evolving herbicide resistance, and a simulation model was developed for understanding the likelihood of glyphosate resistance evolution in this species in cotton-based systems. Under a worst-case scenario of five glyphosate applications in monoculture GR cotton, the model predicts resistance evolution in about 9 yr of continuous glyphosate use, with about 47% risk by year 15. A unique insight from this model is that management in response to GR Palmer amaranth in this system (a reactive response) provided a proactive means to greatly reduce the risks of glyphosate resistance evolution in barnyardgrass. Subsequent model analysis revealed that the risk of resistance is high in fields characterized by high barnyardgrass seedbank levels, seedling emergence, and seed production per square meter, whereas the risk is low in fields with high levels of postdispersal seed loss and annual seedbank loss. The initial frequency of resistance alleles was a high determinant of resistance evolution (e.g., 47% risk at year 15 at an initial frequency of 5e−8 vs. 4% risk at 5e−10). Monte Carlo simulations were performed to understand the influence of various glyphosate use patterns and production practices in reducing the rate and risk of glyphosate resistance evolution in barnyardgrass. Early planting and interrow cultivation are useful tools. Crop rotation is effective, but the diversity of weed management options practiced in the rotational crop is more important. Diversifying weed management options is the key, yet application timing and the choice of management option is critical. Model analyses illustrate the relative effectiveness of a number of diversified glyphosate use strategies in preventing resistance evolution and preserving the long-term utility of glyphosate in midsouthern U.S. cotton-based production systems.

Field studies were conducted in the spring of 1997 and 1998 to quantify the effect of season-long yellow nutsedge interference on watermelon yield. The competitive ability of watermelon with yellow nutsedge was compared in two establishment methods (watermelon transplanted and direct seeded). Critical yellow nutsedge densities and the biological threshold (BT) were used to characterize the competitive ability of watermelon. The critical density in both direct-seeded and transplanted watermelons was 2 yellow nutsedge plants/m2. The BT of yellow nutsedge in seeded watermelons was 37 yellow nutsedge plants/m2, whereas the BT in transplanted watermelons was 25 plants/m2. Transplanting watermelons did not improve their competitive ability with yellow nutsedge. Percent yield loss was similar for both establishment methods at the respective yellow nutsedge densities. Over 40% yield loss was incurred with 12 yellow nutsedge plants/m2 for both establishment methods. Furthermore, it was concluded that watermelons are poor competitors with yellow nutsedge.

Field studies were conducted at three locations during both 2002 and 2003 to evaluate weed control and response of glyphosate-resistant (GR) corn to glyphosate or nicosulfuron plus atrazine applied POST at three application timings with and without alachlor plus atrazine applied PRE. The POST herbicides were applied timely (5- to 9-cm weeds) or applications were delayed 1 or 2 wk. All treatments, except the weedy check, were followed by glyphosate postemergence-directed (PDIR) 4 wk after the timely POST application. Common lambsquarters, common ragweed, Palmer amaranth, prickly sida, and smooth pigweed were controlled at least 94% regardless of PRE or POST treatments. Large crabgrass and fall panicum were controlled at least 96% by glyphosate regardless of PRE herbicide or POST application timing. In contrast, control by nicosulfuron plus atrazine POST in the absence of PRE herbicide decreased as application was delayed. Sicklepod was controlled at least 94% when POST herbicides were applied timely, but control by both POST herbicide treatments decreased with delayed application regardless of PRE herbicide. Tall morningglory was controlled 93% or greater by POST herbicides applied timely. Control by both POST herbicide treatments decreased as application was delayed, with glyphosate being affected more by timing than nicosulfuron plus atrazine. Corn grain yield was similar with glyphosate and nicosulfuron plus atrazine. Yield was unaffected by POST application timing when PRE herbicides were included. Without PRE herbicide, grain yield decreased as POST herbicide application was delayed.