Few herbicides are available for use in lettuce and hand weeding is required for commercially acceptable weed control. More effective herbicides are needed. Here field evaluations of pendimethalin and S-metolachlor for weed control in transplanted lettuce are reported. Pendimethalin was evaluated PRE at rates between 0.6 and 6.7 kg ai ha−1, and POST at 1.1 and 2.2 kg ha−1. Both pendimethalin PRE and POST applications were safe to transplanted lettuce and provided similar weed control. Pendimethalin PRE at rates of 1.1 kg ha−1 and higher provided better weed control than the industry standard, pronamide at 1.3 kg ha−1. S-Metolachlor PRE was evaluated at rates between 0.6 and 5.6 kg ha−1. S-Metolachlor at rates up to 2.8 kg ha−1 caused little or no crop injury or yield reduction in transplanted lettuce, and S-metolachlor at rates of 1.4 kg ha−1 and higher improved weed control compared with pronamide at 1.3 kg ha−1. Pendimethalin and S-metolachlor are not labeled for transplanted lettuce, but we suggest that labeling be pursued at rates of 1.1 and 0.7 kg ha−1, respectively. Pendimethalin at 1.1 kg ha−1 applied PRE or POST improved weed control by 57 and 42%, respectively compared with pronamide. S-Metolachlor PRE at 0.7 kg ha−1 was less effective on weeds than pendimethalin, but maintained weed control level similar to pronamide. Pendimethalin and S-metolachlor have potential for use in transplanted lettuce production and provide alternatives to current transplanted lettuce herbicides.

A study was conducted to quantify the magnitude and sources of variation in common waterhemp temporal patterns of emergence over 1 yr. In 2008 and 2010, emergence patterns in the absence of soil disturbance were determined for replicated samples of maternal families (progeny from one individual) separately harvested during the previous year from four plants within each of four agricultural fields (16 maternal families yr−1) at a university research farm near Urbana, IL. Combining data across years, variance partitioning indicated that seed sample within maternal family explained 48% of total variation in the percentage of viable, buried seeds that produced seedlings. Differences within, rather than among, maternal families also accounted for large fractions (60 to 99%) of total variation in cumulative percentage emergence at specific points during the growing season. Within years, seed samples characterized by delayed or accelerated emergence patterns did not originate from specific maternal plants. These results indicate that common waterhemp seed populations are without strong maternal plant effects that limit emergence to narrow intervals within the overall emergence period. Thus, results of this study support the use of contemporary approaches for modeling herbicide resistance evolution in common waterhemp, which assume seedling cohorts contain offspring from all individuals occurring within the maternal population.

Field studies were initiated in the 2013-14 and 2014-15 growing seasons to evaluate the potential of soil solarization (SS) treatments for their efficacy on weed control and crop yields and to compare SS to 1,3-dichloropropene (1,3-D)+chloropicrin (Pic) fumigation. Each replicate was a bed with dimension 10.6 m long by 0.8 m wide on top. The center 4.6 m length of each bed, referred to as plots, was used for strawberry plug transplanting and data collection. Treatments included: i) 1,3-D+Pic (39% 1,3-dichloropropene+59.6% chloropicrin) that was shank-fumigated in beds at 157 kg ha−1 and covered with VIF on August 30 in both seasons; ii) SS for a 6 wk duration initiated on August 15, 2013 and August 21, 2014 by covering the bed with 1 mil clear polyethylene tarp; iii) SS for a 4wk duration initiated on September 6, 2013 and September 3, 2014; iv) SS 4 wk treatment initiated September 6, 2013 and September 3, 2014 and replaced with black VIF on October 4, 2013 and October 1, 2014 and v) a nontreated control covered with black VIF on October 4, 2013 and October 1, 2014. In both seasons, following completion of the preplant treatments, ‘Chandler’ strawberry was planted in two rows at a 36 cm in-row spacing in plots during the first wk of October. Over both seasons, the 6 wk SS treatment consistently lowered the weed density compared to the nontreated control. Weed density in the 6wk SS treatment was not statistically different from the 4wk SS treatments in the 2013-14 growing season. In both seasons, crop yield in the 4 wk SS was significantly lower than other treatments.

Aminocyclopyrachlor (AMCP) is a herbicide with an auxin-mimic mode of action. AMCP is registered for use in the United States on right-of-way and other noncropland sites, causing concern for potential off-target spray drift. The objectives of this study were to evaluate cantaloupe and eggplant response to simulated AMCP spray drift in the field and cotton response in the greenhouse. Cantaloupe and eggplant responded with little to no injury from drift rates up to 10 g AMCP ha−1, roughly 3.2% of the maximum labeled use rate for right-of-way weed control. Slight yield reductions occurred but were not consistent between 2008 and 2009. Therefore, eggplant and cantaloupe injury and yield-reduction potential from AMCP spray drift is low. Cotton response to AMCP drift was compared to similar spray drift rates of 2,4-D and aminopyralid. Cotton responded with injury and reductions in height and dry mass from all three herbicides. Responses were greatest from AMCP, indicating AMCP is potentially more damaging to cotton than 2,4-D or aminopyralid if spray drift occurs, when comparing percentages of labeled rates.

Understanding the persistence of PRE-applied pendimethalin is important in determining timing of subsequent weed management programs in sugarcane on organic soils in the Everglades Agricultural Area (EAA). Dissipation of oil- and water-based pendimethalin formulations applied PRE at 2, 4, and 8 kg ai ha−1 were compared in 2011 and 2012 on organic soils in the EAA. The rate of dissipation of both formulations was very similar. Both formulations had an initial rapid rate of dissipation followed by a slower rate of dissipation. However, the initial amount of pendimethalin in the soil was higher with the water-based compared to the oil-based formulation, most likely because of the lower volatility of the water-based formulation. The half-lives (DT50s) of the oil-based formulation were 32, 18, and 10 d and 8, 8, and 12 d at 2, 4, and 8 kg ha−1, respectively, in 2011 and 2012, respectively. The DT50s of the water-based formulation were 20, 13, and 10 d and 12, 12, and 14 d at 2, 4, and 8 kg ha−1, respectively in 2011 and 2012, respectively. These DT50 values were attributed to low soil water content as well as the absence of incorporation following application. Our results suggest that dissipation of pendimethalin is rapid on organic soils irrespective of the formulation when applied under dry soil conditions with no incorporation into the soil.

Use of PRE herbicides for control of annual grassy weeds during commercial sod production has been limited. Research was conducted from 2010 to 2013 evaluating the effects of pendimethalin (3.36 kg ai ha−1), dithiopyr (0.56 kg ai ha−1), prodiamine (0.6 kg ai ha−1), oxadiazon (3.36 kg ai ha−1), prodiamine + sulfentrazone (0.84 + 0.41 kg ai ha−1), dimethenamid-P (1.68 kg ai ha−1), and indaziflam (0.03 and 0.05 kg ai ha−1) applications at sprigging on the establishment rate and tensile strength of ‘Tifway' hybrid bermudagrass sod at harvest (377 d after sprigging). All herbicides increased the days required to reach 50% hybrid bermudagrass cover compared with the nontreated control. Days required to reach 50% hybrid bermudagrass cover were lowest for oxadiazon and prodiamine (39 to 44 d), greatest for both rates of indaziflam (65 to 141 d), with dimethenamid-P, prodiamine plus sulfentrazone, pendimethalin, and dithiopyr ranking intermediate (45 to 63 d). Both rates of indaziflam reduced sod tensile strength at harvest compared with the nontreated control during a single year of the study; no other differences in sod strength due to herbicide treatment were detected at any time.

Purple nutsedge is difficult to control in vegetable plasticulture due to its ability to penetrate the plastic mulch. Experiments were conducted in Spring 2011 and 2012 at the Plant Science Research and Education Center in Citra, Florida, and in Spring and Fall 2013 at the Gulf Coast Research and Education Center in Balm, Florida. The objective was to determine tomato (cv. Amelia, Charger, and Florida 47) tolerance and purple nutsedge response to herbicides and herbicide tank-mixes applied POST-directed to base of tomato. Chlorimuron-ethyl, flazasulfuron, fomesafen, halosulfuron, imazosulfuron, rimsulfuron, nicosulfuron, and trifloxysulfuron applied POST-directed to the base of the crop did not cause crop damage. Halosulfuron or tank-mixes that contained halosulfuron tended to provide the greatest nutsedge suppression in all experiments. Halosulfuron or nicosulfuron+rimsulfuron applications when tomato (cv. Charger) were flowering reduced marketable yields by 22-28% compared to the nontreated control. No yield reductions occurred with Florida 47 or Amelia cultivars. Flazasulfuron provided similar purple nutsedge suppression to halosulfuron and did not damage tomato. Tank-mixes that contained halosulfuron tended not to provide any added benefit over halosulfuron alone. This research identified herbicides that are safe for use as a POST-directed application in tomato. Additional research is needed to evaluate efficacy of these herbicides on broadleaf weeds.

Effective POST herbicides and herbicide mixtures are key components of integrated weed management in corn; however, herbicides vary in their efficacy based on application timing. Six field experiments were conducted over 2 yr (2017–2018) in southwestern Ontario, Canada, to determine the effects of herbicide application timing and rate on the efficacy of tolpyralate, a new 4-hydroxyphenyl pyruvate dioxygenase inhibitor. Tolpyralate at 15, 30, or 40 g ai ha−1 in combination with atrazine at 500 or 1,000 g ai ha−1 was applied PRE, early POST, mid-POST, or late POST. Tolpyralate + atrazine at rates ≥30 + 1,000 g ha−1 provided equivalent control of common lambsquarters and Powell amaranth applied PRE or POST, whereas no rate applied PRE controlled common ragweed, velvetleaf, barnyardgrass, or green foxtail. Common ragweed, common lambsquarters, velvetleaf, and Powell amaranth were controlled equally regardless of POST timing. In contrast, control of barnyardgrass and green foxtail declined when herbicide application was delayed to the late-POST timing, irrespective of herbicide rate. Similarly, corn grain yield declined within each tolpyralate + atrazine rate when herbicide applications were delayed to late-POST timing. Overall, the results of this study indicate that several monocot and dicot weed species can be controlled with tolpyralate + atrazine with an early to mid-POST herbicide application timing, before weeds reach 30 cm in height, and Powell amaranth and common lambsquarters can also be controlled PRE. Additionally, this study provides further evidence highlighting the importance of effective, early-season weed control in corn.

Experiments were conducted in North Carolina during 2005, 2006, and 2007 to determine peanut and weed response when peanut was planted in strip tillage after desiccation of cereal rye, Italian ryegrass, oats, triticale, wheat, and native vegetation by glyphosate and paraquat before planting with three in-season herbicide programs. Control of common ragweed and yellow nutsedge did not differ among cover crop treatments when compared within a specific herbicide program. Applying dimethenamid or S-metolachlor plus diclosulam PRE followed by imazapic POST was more effective than a chloroacetamide herbicide PRE followed by acifluorfen, bentazon, and paraquat POST. Incidence of spotted wilt in peanut (caused by a Tospovirus) did not differ when comparing cover crop treatments, regardless of herbicide program. Peanut yield increased in all 3 yr when herbicides were applied POST, compared with clethodim only. Peanut yield was not affected by cover crop treatment. Response to cover crop treatments was comparable, suggesting that growers can select cereal rye, Italian ryegrass, oats, or triticale as an alternative to wheat as a cover crop in peanut systems without experiencing differences associated with in-season weed management.

Understanding the critical time of weed removal (CTWR) is necessary for designing effective weed management programs in popcorn production that do not result in yield reduction. The objective of this study was to determine the CTWR in popcorn with and without a premix of atrazine and S-metolachlor applied PRE. Field experiments were conducted at the University of Nebraska–Lincoln, South Central Agricultural Laboratory near Clay Center, NE in 2017 and 2018. The experiment was laid out in a split-plot design with PRE herbicide as the main plot and weed removal timing as the subplot. Main plots included no herbicide or atrazine/S-metolachlor applied PRE. Subplot treatments included a weed-free control, a non-treated control, and weed removal timing at V3, V6, V9, V15, and R1 popcorn growth stages and then kept weed free throughout the season. A four-parameter log-logistic function was fitted to percentage popcorn yield loss and growing degree days separately to each main plot. The number of growing degree days, when 5% yield loss was achieved, was extracted from the model and compared between main plots. The CTWR was from the V4 to V5 popcorn growth stage in absence of PRE herbicide. With atrazine/S-metolachlor applied PRE, the CTWR was delayed until V10 to V15. It is concluded that, to avoid yield loss, weeds must be controlled before the V4 popcorn growth stage when no PRE herbicide is applied, and PRE herbicide, such as atrazine/S-metolachlor in this study, can delay the CTWR until the V10 growth stage.

Volunteer corn can affect dry bean by reducing yields; expanding the life cycle of insects, mites, and pathogens; interfering with harvest; and contaminating bean seed. Field studies were conducted at Lingle, WY, and Scottsbluff, NE, to determine the relationship between volunteer corn density and dry bean yield, establish the proper time of volunteer corn removal, and determine whether dry bean yield was affected by the method used to remove volunteer corn. Volunteer corn reduced dry bean yields, as recorded in other crops. Growing conditions for each location were different, as indicated by the accumulated growing degree days (GDD): Lingle 2008 (990), Lingle 2009 (780), and Scottsbluff 2009 (957). No difference in dry bean yields was observed between hand removal of volunteer corn and herbicide application. Dry bean yield loss increased with longer periods of volunteer corn competition and ranged from 1.2 to 1.8% yield loss for every 100 GDD that control was delayed. Control measures should be implemented 15 to 20 d after planting when volunteer corn densities are close to 1 plant m−2. Dry bean yield losses also increased as volunteer corn densities increased, with losses from 6.5 to 19.3% for 1 volunteer corn plant m−2. Based on 2015 prices, the cost of controlling volunteer corn would be the equivalent of 102 kg ha−1 of dry bean, and potential losses above 4% would justify control and should not be delayed beyond 15 to 20 d after planting.

Late summer goosegrass control is difficult in turfgrass as POST herbicide efficacy is reduced on mature plants. Field experiments were conducted to evaluate single and sequential nicosulfuron applications tank-mixed with foramsulfuron or sulfentrazone for late summer goosegrass control and safety to bermudagrass and seashore paspalum. All single-treatment applications controlled goosegrass < 62%, whereas sequential sulfentrazone, nicosulfuron, and nicosulfuron + sulfentrazone applications controlled goosegrass 52, 73, and 84%, respectively. Sequential foramsulfuron applications controlled goosegrass < 55% but nicosulfuron tank-mixtures did not improve control. Bermudagrass was injured < 20% by 1 and 3 wk after all single and sequential treatments. Sequential treatments of nicosulfuron alone or tank-mixed with sulfentrazone caused unacceptable seashore paspalum injury (> 20%) 1 and 3 wk after the second application, whereas foramsulfuron or sulfentrazone alone applied sequentially caused < 17% injury. Seashore paspalum seedhead control at 9 wk after intial treatment was poor (< 70%) from all single-application treatments and sequential sulfentrazone applications, but control was good (80 to 89%) to excellent (> 90%) from all other treatments. Overall, sequential treatments of nicosulfuron alone or tank-mixed with sulfentrazone appear to have potential for POST control of mature goosegrass in bermudagrass, but seashore paspalum injury was unacceptable.

In 1994, herbicide efficacy and competitive index databases were adjusted in the soybean herbicide recommendation program HERB to best reflect data for Mississippi. Field experiments were conducted to compare efficacy and economics of postemergence herbicides recommended by HERB and MSU-HERB. The study was conducted utilizing four locations over 2 yr, which provided different soil types, weed spectra, and environmental conditions with which to evaluate weed control from herbicides recommended by these programs. HERB and MSU-HERB agreed on an herbicide recommendation in 62% of the modeling runs. Herbicides recommended by both software versions were generally effective for controlling the predominant weed species at each location. In instances where there was a significant difference in herbicide efficacy between herbicides recommended by HERB and MSU-HERB, improved weed control resulted from herbicides recommended by MSU-HERB. In 1994, excellent moisture conditions enabled soybean to gain a significant competitive advantage over weeds and, as a result, yield loss predictions after treatment were overestimated in most instances. Conversely, 1995 environmental conditions better represented average Mississippi growing conditions, and yield loss predictions after treatment were more accurate. Yield loss prediction accuracy of HERB versions was related to the length of interference between soybean and weeds. Thus, prediction accuracy of HERB and MSU-HERB was similar. Soybean yield increase and net economic gain following MSU-HERB recommendations was as high or higher than following HERB recommendations.

A new, prepackaged mixture of saflufenacil + dimethenamid-P has been introduced for PRE control of grass and broadleaf weeds in corn. Field experiments with this new herbicide combination were conducted in 2008 and 2009 at four locations in southern Ontario, Canada. The objective of this study was to determine the dose of saflufenacil + dimethenamid-P required for overall weed control and species-specific weed control, as well as the dose required for early season weed control when followed with glyphosate at the six- to eight-leaf corn stage. Based on weed dry weight, the GR95 across locations ranged from 126 to 675 g ha−1. The 95% growth reduction (GR95) for common ragweed, common lambsquarters, pigweed, and wild mustard were 933, 325, 186, and 115 g ha−1, respectively. Highest corn yields were achieved with saflufenacil + dimethenamid-P applied alone at doses ranging from 368 to 1470 g ha−1. When followed by glyphosate, the dose range of saflufenacil + dimethenamid-P required to achieve the greatest corn yields was 46 to 1,470 g ha−1. A minimum dose of 184 g ha−1 of saflufenacil + dimethenamid-P followed by glyphosate was required for the yield to exceed that of the single treatment of glyphosate applied alone.

During 1990, injury to tomatoes grown on the narrow land between the Albufera Lake (Spain) and the Mediterranean Sea was attributed to use of irrigation water coming from adjacent rice fields containing bensulfuron and quinclorac. A tomato root bioassay was developed to detect the herbicides in 10 ml of water. The assay was more sensitive to bensulfuron (0.5 ng ml−1) than quinclorac (100 ng ml−1). Only 30 ml of the affected water are necessary to conduct the test. Albufera water, sampled at three sites during 1991 and one during 1992 in the irrigation network canals caused different tomato main root length responses.

Mefluidide, Mon 4620, paclobutrazol plus mefluidide, and flurprimidol plus mefluidide temporarily injured and discolored tall fescue without reducing shoot density. Mefluidide at 0.43 kg ai/ha and Mon 4620 at 2.8 kg ai/ha suppressed vegetative growth of mowed grass 4 weeks while unmowed grass was suppressed for 8 weeks. Mefluidide at 0.14 kg/ha with either flurprimidol at 1.1 kg ai/ha or paclobutrazol at 1.1 kg ai/ha suppressed vegetative growth of mowed tall fescue for 5 and 6 weeks, respectively. Combination treatments also suppressed the growth of nonmowed tall fescue 8 to 10 weeks. Mowing effectively suppressed seedheads for 12 weeks when the grass was mowed at 3 and 6 weeks, while mowing only once at 4 weeks did not. Seedhead suppression was not improved with weekly mowing compared with two mowings. Mowing influenced the performance of plant growth regulators on vegetative growth and seedhead control but not plant injury, quality, or shoot density.

Studies were conducted at three locations in North Carolina in 2004 to evaluate density-dependent effects of glyphosate-resistant (GR) corn on GR cotton growth and lint yield. GR corn was taller than GR cotton as early as 25 d after planting, depending on location. A GR corn density of 5.25 plant/m of crop row reduced late season cotton height by 49, 24, and 28% at Clayton, Lewiston–Woodville, and Rocky Mount, respectively, compared to weed-free cotton height. At Clayton, GR corn dry biomass per m crop row and GR corn seed biomass per m of crop row decreased linearly with increasing corn density. The relationship between GR corn and GR cotton yield loss was described by the rectangular hyperbola model with the asymptote (a) constrained to 100% maximum yield loss. The estimated coefficient i (yield loss per unit density as density approaches zero) was 9, 5, and 5 at Clayton, Lewiston–Woodville, and Rocky Mount, respectively. The examined GR corn densities had a significant effect on cotton yield, but not as significant as many other problematic grass and broadleaf weeds.

Infestations of Italian ryegrass are difficult to control and decrease marketability of cool-season sod. Tests were conducted at three locations in Virginia in 2002 and 2003 to determine herbicide control options for Italian ryegrass in 90:10 tall fescue: Kentucky bluegrass turfgrass seeded the previous fall. Chlorsulfuron, diclofop, fluazifop plus fenoxaprop, and metsulfuron controlled 5- to 30-tiller Italian ryegrass less than 50% 10 wk after initial treatment (WAIT). Nicosulfuron at 53 g ai/ha controlled Italian ryegrass 69 to 95% and injured turf no greater than 10% at all locations 10 WAIT. Primisulfuron at 53 g ai/ha controlled Italian ryegrass less than 30% in 2002 and 59 to 63% at two locations in 2003 10 WAIT and injured turf less than 5% at all locations. Results indicate nicosulfuron can be used for Italian ryegrass control in tall fescue or tall fescue and Kentucky bluegrass turf if temporary injury is acceptable.

Experiments were conducted in the greenhouse and the field to determine the influence of various oil adjuvants on small grain and grass weed susceptibility to foliarly applied BAS-514 OO H (BAS-514). Barnyardgrass, green foxtail, and yellow foxtail were more susceptible to BAS-514 at 0.56 kg ai ha-1 applied with than without an oil adjuvant. Shoot fresh weight reductions of barnyardgrass, green foxtail, and yellow foxtail were greater when BAS-514 at 0.56 kg ha-1 was applied with a methylated seed oil than with a petroleum oil adjuvant in the greenhouse. Differences in the effectiveness among oil adjuvants in enhancing BAS-514 phytotoxicity were more evident in greenhouse than in field experiments. Oil adjuvant enhancement of BAS-514 varied with plant species. Oats, hard red spring wheat, and winter wheat tolerated BAS-514 at 1.1 kg ha-1 foliarly applied with or without an oil adjuvant in the greenhouse. BAS-514 at 0.56 kg ha-1 applied with oil adjuvants caused less than 5% injury to wheat in the field.

Canada thistle is one of the most troublesome and difficult weed species to control in established alfalfa grown for seed production. Current tools available for control are limited because of cultural management strategies associated with seed production. Alfalfa seed losses due to Canada thistle interference include both reduced yields from competition and increased seed loss during seed cleaning operations. Additional tools are needed to alleviate these losses. Field experiments were conducted in 1998, 1999, and 2000 at two locations in Park County, WY, to evaluate Canada thistle control and alfalfa tolerance to several postemergence herbicides. Bentazon, imazamox, imazethapyr, and MCPB were applied, alone or in combination, at different Canada thistle growth stages. Methylated seed oil (MSO) was added at 1.5% v/v to the treatments containing imazamox or imazethapyr. MCPB applied alone when Canada thistle was 7.5- or 15-cm tall caused severe alfalfa injury (28 to 40%) and resulted in less Canada thistle control (23 to 27%). Imazamox or imazethapyr applied alone when Canada thistle was 15-cm tall did not cause any significant alfalfa injury but resulted in unsatisfactory Canada thistle control (29 to 35%). Bentazon was the only treatment containing a single herbicide that provided more than 50% Canada thistle control. The treatments providing the best balance between Canada thistle control (>80%) and alfalfa injury (<13%) were a single application of bentazon combined with either imazamox or imazethapyr. These two treatments also yielded the highest, more than 800 kg/ha. Split applications of bentazon combined with imazamox or imazethapyr were similar to single applications.