Glyphosate resistance in weed species has presented immense challenges for farmers in Ontario. The co-application of burndown plus residual herbicides provides control of glyphosate-resistant (GR) horseweed in soybean. Pyraflufen-ethyl/2,4-D is a premixed herbicide formulation sold under the tradename Blackhawk®. Five field experiments were conducted over a 2-yr period (2019, 2020) in fields in southwestern Ontario to ascertain the biologically effective dose of pyraflufen-ethyl/2,4-D, applied alone, or mixed with metribuzin, for GR horseweed control when applied preplant to soybean. Soybean visible injury for all treatments was <15%. At 8 wk after application (WAA), the calculated doses of pyraflufen-ethyl/2,4-D for 50%, 80%, and 95% control of GR horseweed were 390, 1,148, and >2,108 g ha−1, respectively. The addition of metribuzin to pyraflufen-ethyl/2,4-D reduced the doses of pyraflufen-ethyl/2,4-D for 50%, 80%, and 95% control of GR horseweed to 19, 46, and 201 g ha−1, respectively. Pyraflufen-ethyl/2,4-D + metribuzin controlled GR horseweed by 97%, which is comparable to the current industry standards. Based on these results, pyraflufen-ethyl/2,4-D + metribuzin (527 + 400 g ha−1) applied preplant can be used for GR horseweed control in soybean.

We conducted research to evaluate various herbicides for POST false-green kyllinga control in cool-season turfgrass (primarily creeping bentgrass). In a preliminary evaluation, single and sequential applications of halosulfuron-methyl (70 g ai ha−1), mesotrione (175 g ai ha−1), and sulfentrazone (140 g ai ha−1), as well as a single application of imazosulfuron (740 g ai ha−1), were evaluated in New Jersey. Imazosulfuron and sequential applications of halosulfuron-methyl controlled false-green kyllinga >93% at 9 and 18 wk after initial treatment (WAIT). Sulfentrazone and mesotrione controlled false-green kyllinga <50%. Additional experiments were conducted to evaluate single and sequential applications of halosulfuron-methyl (70 g ha−1), imazosulfuron (420 and 740 g ha−1), and sulfentrazone (140 g ha−1) in New Jersey and Indiana at two locations in each state. At 12 WAIT, imazosulfuron generally controlled false-green kyllinga more effectively than other treatments at all locations. Sequential applications of imazosulfuron controlled false-green kyllinga 100% at 12 WAIT. Halosulfuron-methyl was less effective in Indiana than in New Jersey. Sulfentrazone controlled false-green kyllinga <40% at 12 WAIT. This research demonstrates that imazosulfuron is more effective than halosulfuron-methyl and sulfentrazone for POST false-green kyllinga control in cool-season turf.

Resistant plants of Sumatran fleabane with unusual rapid necrosis (RN) symptoms after application of 2,4-D were characterized in previous studies. Field observations indicated variability in the occurrence of the RN caused by 2,4-D, but the causes of the variation are unknown. This study aimed to investigate the effect of environmental conditions, plant growth stage, and simultaneous and sequential herbicide mixtures with other auxin mimics on the occurrence of RN caused by 2,4-D. Application at temperature of 12 C delayed the symptoms and decreased the intensity of the RN but still resulted in plant survival to 2,4-D. The absence of light after herbicide application caused a slight delay in the symptoms, but the production of hydrogen peroxide and the size of the necrosed area were not affected by the light treatments before and after 2,4-D application. Changes in plant photosynthesis through inhibiting photosystem II do not prevent the occurrence of RN symptoms. The auxinic herbicides dicamba, triclopyr, and halauxifen-methyl do not cause RN symptoms and are effective at controlling the resistant biotype when applied without 2,4-D, but the effectiveness of these herbicides was reduced when sprayed on the resistant biotype either together, 4 h, or 24 h after 2,4-D. The RN phenotype does not occur for dicamba and triclopyr, even in advanced plant growth stages and high doses on the resistant biotype. The herbicides dicamba and triclopyr effectively controlled resistant plants, especially when sprayed at the initial growth stages. The results of this study identify environmental effects, plant development effects, and herbicide interactions that interfere with the occurrence of RN symptoms caused by 2,4-D in Sumatran fleabane. These data provide insights about the mechanisms behind the RN symptoms caused by 2,4-D and are important for identifying the causes of variability of the herbicide symptomology and performance under experimental and field conditions.

Desmedipham applied at 0.5 kg ai/ha at the 4-leaf stage of common buckwheat controlled wild mustard over 90%. Desmedipham at 1.0 kg/ha at the 2- and 6-leaf stages also controlled wild mustard approximately 90%, at least in 1985, but significantly injured the crop. Fluorochloridone controlled wild mustard over 90% when applied preplant incorporated at 1.0 kg ai/ha or preemergence at 0.28 to 0.56 kg/ha. Fluorochloridone applied postemergence at 0.10 to 0.20 kg/ha also controlled wild mustard over 90% but injured common buckwheat by 41 to 57%.

Dry bean cultivars were evaluated for suppression of late-season weed emergence near Scottsbluff, NE in 1993 and 1994. The 12 cultivars differed in plant canopy architecture and the amount of light intercepted. In 1993, the vine growth habit of Pinto ‘D-84354’ provided a more dense canopy and more yellow foxtail suppression than Pinto ‘RS-101’ that had an upright growth habit. Growing season also influenced plant canopy and late season weed emergence. Cooler temperatures in 1993 resulted in a less dense Navy ‘Mayflower’ canopy which provided less redroot pigweed suppression than warmer conditions in 1994 that resulted in a more dense crop canopy. No difference in weed suppression was observed among cultivars for common lambsquarters, common purslane, and hairy nightshade.

Field studies were conducted in 2006 and 2007 to evaluate the tolerance of autumn-planted cabbage and turnip green to halosulfuron applied the previous spring to cantaloupe. Main plots were three levels of soil pH: maintained at a natural pH level, pH raised with Ca(OH)2, and pH lowered with Al2(SO4)3. Subplots were a factorial arrangement of two halosulfuron application methods and three halosulfuron rates. Halosulfuron application methods were PPI or POST after transplanting to the edges of mulch-covered seedbeds. Halosulfuron rates were 35 and 70 g ai/ha, along with a nontreated control. Cantaloupe were transplanted, maintained weed-free, and evaluated for yield response. After cantaloupe harvest, direct-seeded turnip green and transplanted cabbage were established in September of each year and evaluated for crop tolerance and yield. Data indicated nonsignificant main effects of soil pH and halosulfuron application method on cantaloupe yield. However, in 2007 cantaloupe yields were significantly reduced, by 16 and 20% for halosulfuron applied at 35 and 70 g/ha, respectively. For all turnip green and cabbage response parameters, interactions were nonsignificant between application method and rate, soil pH and rate, and soil pH and application method, along with the three-way interaction. After 6 mo, there was no evidence of stunting from halosulfuron carryover in 2006 to direct-seeded turnip green and in both years to transplanted cabbage. Visual estimates of stunting to direct-seeded turnip green ranged from 9 to 16% for halosulfuron at 35 and 70 g/ha, respectively, in 2007, but all stunting was transient and turnip green yield was not affected.

Goatsrue response to eight herbicide treatments was evaluated in greenhouse and field trials. Herbicides tested on goatsrue grown from seed in the greenhouse included 2,4-D amine, dicamba, chlorsulfuron, picloram, imazapyr, imazamox, aminopyralid, and triclopyr. Each herbicide was applied at rates of 0.125×, 0.25×, 0.5×, 1.0×, and 2.0×, where X is equal to the labeled rate. Goatsrue was most sensitive to the acetolactate synthase inhibitors chlorsulfuron and imazapyr, with 50% inhibition values of 0.07× (3.7g ai ha−1) and 0.16× (90 g ai ha−1) respectively. Goatsrue did not respond to increasing 2,4-D and imazamox rates. Herbicides evaluated in the greenhouse were also tested at two field sites (Smithfield and Amalga, UT), except imazamox, which was replaced by metsulfuron. Field studies gave some varying results, but overall showed that chlorsulfuron, metsulfuron, aminopyralid, and picloram gave at least 93% control at Smithfield, and 89% control at Amalga 24 mo after treatment (MAT). Treatments of chlorsulfuron, metsulfuron, aminopyralid, and picloram were also effective at increasing perennial grass cover at Smithfield 24 MAT. All treatments at Smithfield decreased seedling goatsrue cover, whereas only aminopyralid and picloram decreased seedling cover at Amlaga 11 MAT.

The presence of row crops, such as field corn, improves herbicidal control of weeds, but the impact of crop row position on herbicide dose–response relationships for weeds is unknown. At midseason at three site-years in Missouri, total weed cover (WC) was reduced by increasing soil residual herbicide rate in a dose-dependent response and was as much as 20% lower in-row (IR) than between-row (BR). Preemergence atrazine + S-metolachlor + clopyralid + flumetsulam at different rates (0×, 0.25×, 0.5×, 0.75×, and 1×, where 1× rate was 2,240 + 1,750 + 210 + 67 g ai/ha, respectively) were applied at planting in field corn to control giant foxtail, the chief weed present, and annual broadleaf weeds, largely common waterhemp. Lower herbicide rates were required to reduce IR WC to the same extent as BR WC, but these rates varied between site-years. At all three site-years, a least squares regression equation adequately described data variability relating corn yield to IR or BR WC (or both) (i.e., Y = a + bBR2, where Y is corn yield in kg/ha, BR is BR WC [%], and a and b are coefficients).

The primary aim of seed companies is to provide products that the customer wants to buy, and to sell them at a profit. Future demands for improved cultivars of major field crops will continue to be primarily for those with reliably high yield and desirable quality. Herbicide tolerance will not be a primary determinant in cultivar choice for most customers. Therefore, seed companies probably will move with caution in development of herbicide-tolerant cultivars.

Field trials were conducted in Virginia during 2000 and 2001 to evaluate long-term trumpetcreeper control in corn with dicamba, BAS 654 plus dicamba, 2,4-D, CGA 152005 plus primisulfuron, halosulfuron, primisulfuron, and mesotrione. Each of these herbicides was applied alone as a single postemergence (POST) treatment or as a component of a POST herbicide combination. Trumpetcreeper suppression ratings 3 mo after treatment (MAT) revealed a general trend toward higher levels of suppression with combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with any of the sulfonylurea herbicides and lower levels of suppression with applications of any of the sulfonylurea herbicides alone. Combinations of dicamba, BAS 654 plus dicamba, or 2,4-D with mesotrione also provided some of the highest levels of trumpetcreeper suppression 3 MAT in both years. At 1 yr after treatment (YAT), 2,4-D alone, BAS 654 plus dicamba, CGA 152005 plus primisulfuron plus 280 g ai/ha dicamba, primisulfuron plus 280 g/ha dicamba, primisulfuron plus 2,4-D, mesotrione plus BAS 654 plus dicamba, and mesotrione plus 2,4-D reduced trumpetcreeper stem density by at least 52% when compared with that of the nontreated control. These herbicide treatments were the only ones that provided reductions in trumpetcreeper stem density 1 YAT when compared with that of the nontreated control. In 2000 and 2001, there were few differences in corn yield among the treatments evaluated in these trials, and no treatment resulted in corn yields that were lower than the nontreated control. Acceptable trumpetcreeper suppression may be achieved during the season of treatment with any of these herbicide combinations, but only a few treatments will provide long-term trumpetcreeper control.

Soil cultivation (3 to 5 times/yr) and herbicide management (oxadiazon, 3.92 kg ai/ha), agricultural standards for reducing weed competition, were compared to three alternative nursery field management systems regarding weed suppression: ‘Norcen’ bird's-foot trefoil companion crop, ‘Wheeler’ winter rye cover crop/mulch, and grass sod (80% ‘Eton’ perennial ryegrass and 20% ‘Ruby’ red fescue). Field management treatment had a significant effect on observed weed populations. Weed densities were also subject to yearly variations caused by climate and endogenous weed life cycles. Herbicide management (oxadiazon) consistently provided the best control of undesired vegetation (0.3 weeds/m2) followed by the grass sod (0.7 weeds/m2), Wheeler rye cover crop/mulch (1.7 weeds/m2), Norcen bird's-foot trefoil companion crop (8.6 weeds/m2), and cultivated (55.7 weeds/m2) treatments, respectively. Although the grass sod treatment provided excellent control of undesired vegetation, as an alternative to cultivation and herbicide use, it proved to be excessively competitive with the nursery crop. The bird's-foot trefoil treatment quickly became infested with broadleaf weeds the eradication of which proved difficult. The Wheeler winter rye cover crop/mulch field management system provided acceptable weed control combined with other beneficial effects on the plant/soil environment. Results support the effectiveness of Wheeler winter rye and perhaps other allelopathic cover crop/mulch systems in controlling undesired vegetation in horticultural field production systems.

The tolerance of 10 broccoli cultivars to preemergence (PRE) applications of oxyfluorfen was evaluated in greenhouse and field experiments. Differences in tolerance among cultivars were expressed as differences in seedling injury ratings and growth and stand reduction. The cultivars ‘Pinnacle’ and ‘Mercedes’ were most tolerant, ‘Embassy’ and ‘Early Dawn’ were least tolerant, and other cultivars were intermediate in tolerance. Broccoli seedling weights and stand counts averaged across 10 cultivars and oxyfluorfen application rates of 0.125, 0.25, and 0.5 kg/ha were 70 and 81% of control, respectively, for the two fall-planted experiments and 39 and 50% of control, respectively, for the spring-planted experiment. Differences in tolerance among cultivars were less distinct in the cooler spring than in the warmer fall season. Oxyfluorfen application that caused stand and early growth reduction did not always affect broccoli head weight or quality or delay harvest.

Premergence (PRE) herbicides were applied to a bermudagrass golf green overseeded with ‘Laser’ roughstalk bluegrass during 1995 and 1996 to determine their effects on roughstalk bluegrass injury and on the transition from a mixed cool- and warm-season grass back to the permanent bermudagrass. Roughstalk bluegrass tolerated single March applications of trifluralin plus benefin at 2.2 kg/ha, pendimethalin at 3.4 kg/ha, dithiopyr at 0.6 kg/ha, prodiamine at 0.8 kg/ha, bensulide plus oxadiazon at 8.4 kg/ha, and bensulide at 11.2 kg/ha. A single March application of oxadiazon plus benefin at 3.4 kg/ha severely injured (35%) the overseeded turf in 1 yr, but not when 1.7 kg/ha was applied in March and repeated in May. One-half recommended rates of oxadiazon and bensulide plus oxadiazon applied in March did not cause any undesirable injury, but when repeated in May, moderate to severe injury (28 to 33%) occurred in June. Oryzalin at ≥ 1.1 kg/ha, benefin plus oryzalin at ≥ 1.1 kg/ha, and oxyfluorfen plus oryzalin at ≥ 1.7 kg/ha severely injured (≥ 35%) roughstalk bluegrass. The rate of transition of mixed roughstalk bluegrass and bermudagrass back to permanent bermudagrass was not affected by any of the PRE herbicides except when oryzalin was applied alone or in combination with benefin or oxyfluorfen.

Virginia creeper and wild grape are troublesome perennial vines that often infest Christmas tree plantations. Field studies were conducted to evaluate Fraser fir injury and Virginia creeper and wild grape control with directed applications of triclopyr (1,680 g ai/ha) alone and in combination with 2,4-D (1,120 g ai/ha), clopyralid (280 g ai/ha), and halosulfuron (36 g ai/ha). Additional treatments included 2,4-D, clopyralid, glyphosate (1,120 g ai/ha), halosulfuron, hexazinone (560 g ai/ha), mesotrione (105 g ai/ha), and sulfometuron (71 g ai/ha) applied alone; and a mixture of hexazinone plus mesotrione. In the triclopyr-containing treatments, Fraser fir injury ranged from 6 to 13% at 1 mo after treatment (MAT) and was 4 to 8% at 11 MAT. Leader growth was not impacted by the herbicide treatments. At 11 MAT, all triclopyr-containing treatments controlled Virginia creeper 93 to 98% and wild grape 98 to 100%, which was greater than the control observed with glyphosate at 63 and 59%, respectively. Virginia creeper and wild grape control with 2,4-D was 88 to 90%. Clopyralid, halosulfuron, hexazinone, hexazinone plus mesotrione, mesotrione, and sulfometuron provided less than 66% control of both perennial vines. Directed applications of triclopyr-containing treatments or 2,4-D were effective management tools for selective removal of wild grape and Virginia creeper from Fraser fir Christmas tree plantations. Additional research is needed on the potential sensitivity of other commonly grown Christmas tree species to triclopyr-containing treatments.

Experiments were conducted from 1989 through 1991 to determine the effect of MSMA on efficacy of fluometuron, cyanazine, oxyfluorfen, lactofen, methazole, diuron, and linuron applied POST to entireleaf morningglory. In one set of experiments, applications were made at the cotyledon to three-leaf and four- to six-leaf stages of weed growth. In another set of experiments, applications were made at only one growth stage. Cyanazine, MSMA, or cyanazine plus MSMA were the most efficacious treatments, especially when application was delayed until the four- to six-leaf stage. Adding MSMA to all of the herbicides increased control of entireleaf morningglory, with the magnitude of improvement increasing as the application timing was delayed.

Studies were conducted to evaluate absorption and translocation of 14C-glyphosate in glyphosate-resistant (GR) cotton. Both commercial GR cotton events [glyphosate-resistant event 1, marketed as Roundup Ready®, released 1997 (GRE1), and glyphosate-resistant event 2, marketed as Roundup Ready Flex®, released 2006 (GRE2)] were evaluated at the four-leaf and eight-leaf growth stages. Plants were harvested at 1, 3, 5, and 7 d after treatment (DAT). Glyphosate absorption, as a percentage of applied, increased over time with 29 and 36% absorption at 7 DAT in four-leaf GRE1 and GRE2 cotton, respectively. In eight-leaf cotton, glyphosate absorption (33% at 7 DAT) was not different between events. Glyphosate translocation patterns were not different between events or harvest timings and exhibited a source–sink relation. Observed translocation differences between cotton growth stages were probably due to reduced glyphosate export from the treated leaf of eight-leaf cotton. An additional study compared absorption and translocation of 14C-glyphosate and 14C-sucrose in 5- and 10-leaf GRE2 cotton. Averaged over trials, 14C compounds, and growth stages, cotton absorbed 28% of the applied dose at 14 DAT. On the basis of the percentage of 14C exported out of the treated leaf, glyphosate and sucrose translocation patterns were similar, indicating that glyphosate may be used as a photoassimilate model in GRE2 cotton.

Picloram was applied broadcast on kleingrass pastures in the spring either as sprays or as pellets containing 2, 5, or 10% ae. The carrier in 5 and 10% pellets was inert clay, but 2% pellets were formulated with sufficient ammonium sulfate to contain 14.4% N. Dry formulations of picloram (10% ae), dicamba (5% ae), and tebuthiuron (20% ai) were compared to sprays at equal rates in a coastal bermudagrass pasture. Picloram was more effective as a spray than as pellets in two of five experiments. Few differences in weed control were observed with 2, 5, and 10% picloram pellets. Picloram applied up to 3 kg ae/ha as 2% pellets did not reduce kleingrass standing crop and up to 29 kg/ha of N as ammonium sulfate applied with or without picloram did not increase kleingrass production. None of the herbicides controlled weeds during the year following application.

Midwest growers rely heavily on agrichemical retailers and crop consultants for making pest management decisions. A survey was mailed to 793 fertilizer and agricultural chemical dealers in Illinois to help understand their basis for pesticide recommendations, sources of information, and water quality concerns. Survey response rate was approximately 55%, and results indicated that agrichemical retailers use several sources of information, including manufacturers, universities, and company training programs. Newsletters and fact sheets were recognized as the most useful types of university resources, whereas videos were deemed the least useful. Product effectiveness was identified by 85% of the respondents as being the most important factor affecting pesticide selection. Soil erosion was listed as the greatest threat to water quality. Filter strips and best management practices were suggested as being the most likely to succeed in protecting water quality.

In strip-tillage peanut production, situations occur when dinitroaniline herbicides are not applied in a timely manner. In these cases, dinitroaniline herbicides would be applied days or weeks after seeding. However, there is no information that documents the effects of delayed applications on weed control. Trials were conducted in 2004, 2005, and 2007 in Georgia to determine the weed control efficacy of delayed applications of pendimethalin in strip-tillage peanut production. Treatments included seven timings of pendimethalin application and three pendimethalin-containing herbicide combinations. Timings of application were immediately after seeding (PRE), vegetative emergence of peanut (VE), 1 wk after VE (VE+1wk), VE+2wk, VE+3wk, VE+4wk, and a nontreated control. Pendimethalin containing herbicide programs included pendimethalin plus paraquat, pendimethalin plus imazapic, and pendimethalin alone. Among the possible treatment combinations was a current producer standard timing for nonpendimethalin weed control programs in peanut, which was either imazapic or paraquat alone applied VE+3wk. Pendimethalin alone did not effectively control Texas millet regardless of time of application (69 to 77%), whereas southern crabgrass was controlled by pendimethalin alone PRE (87%). Delayed applications of pendimethalin controlled Texas millet and southern crabgrass when combined with either paraquat or imazapic, with imazapic being the preferred combination due to better efficacy on southern crabgrass than paraquat at most delayed applications. Peanut yield was improved when any of the herbicide combinations were applied PRE compared to later applications. Across all times of application, pendimethalin plus imazapic effectively maximized peanut yield with interference from annual grasses.

Diclofop and dithiopyr were applied in April and early May during 1992 and 1993, to a ‘Tifway’ bermudagrass golf green overseeded with perennial ryegrass, to determine the effects of rates and dates on perennial ryegrass injury and on transition from a mixed cool- and warm-season grass to bermudagrass turf. Diclofop applied as a single application at 0.6 kg/ha or two applications at 0.3 kg/ha during April and/or early May gradually reduced perennial ryegrass during June and July when compared with untreated turf. During this period, both grasses treated with diclofop maintained 94% or greater cover. However, perennial ryegrass was moderately to severely injured from the treatments. Maximum injury from the 0.6 kg/ha rate ranged from 40 to 55% during 1992 and 29 to 33% during 1993. The injury was pronounced over a period of one to three weeks. Maximum injury from 0.3 kg/ha applied on April 3 and repeated at the same rate on April 17 was 28% in 1992 and 37% in 1993. Perennial ryegrass injury from split applications was lower than from the single 0.6 kg/ha rate in 1992. The optimum time and rate for effective spring transition with least amount of perennial ryegrass injury was 0.3 kg/ha applied on April 5 and repeated at the same rate on April 17. Dithiopyr did not affect the spring transition of overseeded perennial ryegrass to bermudagrass, regardless of rate and application date.