The tolerance of cereal rye to eight herbicides registered for use in wheat, at two rates, was evaluated for potential labeling in cereal rye to expand limited chemical weed control options. Across five site-years, halauxifen-methyl + florasulam, pyroxsulam, and thifensulfuron-methyl + tribenuron-methyl applied at a 2X rate to cereal rye at Zadoks (Z) 13 caused less than 15% injury and had no impact on cereal rye density. These herbicides at the 2X rate reduced cereal rye heights 11% at 10 days after treatment (DAT), with rye recovering by 31 DAT; cereal rye heights were not reduced with these herbicides at their 1X rate. In contrast, significant injury was observed with the 1X rate of mesosulfuron-methyl (45%), pinoxaden (27%), and pinoxaden + fenoxaprop-P-ethyl (30%) applied postemergence; early-season height was reduced 19% to 26%. Residual herbicide pyroxasulfone applied as a delayed preemergence at Z 10 and flumioxazin + pyroxasulfone applied at Z 11 caused 27% to 28% and 16% to 47% injury, respectively, when the 1X rate was activated by rainfall within 2 d of application. These residual herbicides reduced cereal rye height and density up to 35% and 40%, respectively. Cereal rye grain yield was not influenced by herbicide or rate applied.

POST weed control atop the bed during strawberry production is limited to hand weeding, clopyralid, and acetyl CoA carboxylase inhibitors. Identification of additional modes of action is desirable to increase available options for producers and alleviate herbicide resistance concerns. The study objective was to screen sulfonylurea herbicides for safety of strawberry coordinated with efficacy against Carolina geranium. Herbicide treatments included metsulfuron-methyl, flazasulfuron, foramsulfuron, thifensulfuron-methyl, trifloxysulfuron-sodium, and rimsulfuron. Strawberry plants were heavily damaged by all herbicides apart from foramsulfuron. Although the strawberry plant was dramatically affected by the evaluated herbicides, demonstrating strong epinasty, there were no differences in resultant biomass at 31 d after treatment (DAT) compared to controls. Carolina geranium was severely injured by metsulfuron-methyl, flazasulfuron, and thifensulfuron-methyl, and moderately injured by foramsulfuron. There were consistent reductions in biomass by 31 DAT by metsulfuron-methyl and flazasulfuron. Overall, metsulfuron-methyl and flazasulfuron are suitable candidates for Carolina geranium control in row-middles. Foramsulfuron is a suitable candidate for additional field-based screening for utility in POST use in strawberry production atop the bed. Consideration toward doses, surfactants, timings, and cultivar tolerance may be necessary to minimize injury as observed in the greenhouse (15% to 20%).

Field studies were conducted at the Pontotoc Ridge–Flatwoods Branch Experiment Station in Pontotoc, MS, in 2016 and 2017 to determine sweetpotato crop response to saflufenacil and rimsulfuron/thifensulfuron-methyl. Saflufenacil treatments consisted of a factorial of two rates (25 or 50 g ai ha–1) by three application timings [0, 3, or 6 wk before transplanting (WBP)]. Rimsulfuron/thifensulfuron-methyl treatments consisted of a factorial of two rates (18/18 or 35/35 g ai ha–1) by two application timings (3 or 6 WBP). A nontreated check was included for comparison. Saflufenacil resulted in as much as 20% stunting injury in 2016, but ≤4% crop injury in 2017. Compared to the nontreated check, saflufenacil did not reduce yield of any sweetpotato grade regardless of application rate or timing. Findings from this trial indicate that saflufenacil applied in pre-transplanting burndown and field preparation procedures did not have a negative impact on the subsequent sweetpotato crop and that the current plant-back interval (4 to 5 mo) may be excessive. Applications of rimsulfuron/thifensulfuron-methyl at 35/35 g ha–1 made 3 WBP resulted in significant crop injury but did not reduce yield of any sweetpotato grade. Findings from this trial suggest that rimsulfuron/thifensulfuron-methyl applications up to 35/35 g ha–1 applied at least 6 WBP and 18/18 g ha–1 applied at least 3 WBP had little impact on sweetpotato crop growth and may be a safe preplant burndown option.

Control of broadleaf weeds in caladium is difficult due in part to a lack of selective POST herbicides. Cultivation is not an option due to the dense canopy and potential for tuber injury. As a result, growers currently rely on preemergence (PRE) herbicide and hand-weeding. The objective of this research was to evaluate the control of four common broadleaf weeds of field grown caladium with POST applications of halosulfuron, thifensulfuron-methyl, and trifloxysulfuron, and determine the tolerance of caladium cultivars ‘Florida Fantasy’ and ‘Florida cardinal’ to POST applications of halosulfuron. At 4 weeks after treatment (WAT), thifensufluron-methyl at 28 g ai ha−1 and trifloxysulfuron at 84 g ai ha−1 provided approximately 90 and 70% common purslane control, respectively, while halosulfuron at 210 g ai ha−1 provided 55% suppression. Trifloxysulfuron controlled ≥90% spotted spurge at 42 g ha−1, whereas the highest rate of halosulfuron and thifensulfuron-methyl only achieved 60% suppression. In field experiments, the evaluated sulfonylurea (SU) herbicides were less efficacious on hairy indigo and sharppod morningglory as control never exceeded 65 and 50%, respectively. In greenhouse experiments, the evaluated halosulfuron rates ranging from 26 to 420 g ha−1 did not significantly reduce caladium tuber weight from the nontreated control. Averaged over halosulfuron rates, ‘Florida Fantasy’ damage was 5 and 6% at 2 and 4 WAT, respectively, while ‘Florida Cardinal’ damage was 11%. We conclude that none of the herbicide treatments effectively controlled all species evaluated. Sequential treatments, higher rates, or tank-mixtures may be necessary to adequately control these species. We also conclude that caladium cultivars ‘Florida Fantasy’ and ‘Florida Cardinal’ have acceptable tolerance to POST applications of halosulfuron. Further research is needed to evaluate caladium tolerance to other SU herbicides.

Glyphosate-resistant giant ragweed is one of the most competitive weeds of agronomic crops in the United States. Early emergence and rapid growth rate makes giant ragweed a competitive weed early in the season and reduces crop yields. Therefore, early spring control of giant ragweed using a preplant herbicide is critical. Glufosinate is an alternative POST herbicide for weed control in glufosinate-resistant soybean. Field experiments were conducted at David City, NE, in 2012 and 2013 to evaluate the efficacy of preplant herbicides followed by glufosinate applied alone or in tank mixes for control of glyphosate-resistant giant ragweed in glufosinate-resistant soybean. Preplant treatments containing 2,4-D, flumioxazin, glufosinate, paraquat, saflufenacil, and sulfentrazone provided 79 to 99% control of giant ragweed 21 d after treatment (DAT), and subsequent application of glufosinate alone or in tank mixes resulted in 90 to 99% control at 21 DAT. Preplant application of S-metolachlor plus metribuzin or chlorimuron, flumioxazin plus thifensulfuron followed by glufosinate resulted in < 40% control of giant ragweed, and soybean yields were < 870 kg ha−1. Although statistically comparable to several other treatments, preplant application of 2,4-D or saflufenacil tank mixes followed by glufosinate resulted in the highest level of control (> 97%) and soybean yield (2,624 to 3,378 kg ha−1). This study confirms that preplant herbicide options are available for control of glyphosate-resistant giant ragweed, and a follow-up application of glufosinate will provide season-long control in glufosinate-resistant soybean.

Field experiments were conducted in 2001 and 2002 to evaluate the efficacy of herbicides on protoporphyrinogen oxidase (protox, EC 1.3.3.4) inhibitor–resistant common waterhemp in corn and soybean. All corn herbicides tested gave greater than 90% common waterhemp control by 8 wk after postemergence herbicide treatment (WAPT). In soybean, common waterhemp control was less than 40% by 8 WAPT with postemergence protox-inhibiting herbicides lactofen and acifluorfen. However, preemergence protox-inhibiting herbicides sulfentrazone and flumioxazin gave greater than 85% common waterhemp control in both years. The greatest common waterhemp control in soybean was with glyphosate alone, alachlor + metribuzin, alachlor followed by (fb) glyphosate, and S-metolachlor + metribuzin fb glyphosate.

Field studies were conducted in 1995 and 1996 to investigate postemergence (POST) applications of rimsulfuron (12 g ai/ha) plus thifensulfuron-methyl (6 g ai/ha) in tank-mixtures with various acetolactate synthase (ALS)- and non–ALS-inhibitor herbicides for weed control in corn. Rimsulfuron plus thifensulfuron-methyl controlled giant foxtail and common lambsquarters at least 95% but did not control common ragweed. Rimsulfuron plus thifensulfuron-methyl tank-mixed with 20 g ai/ha primisulfuron-methyl, 17 g ai/ha CGA-152005 plus 18 g ai/ha primisulfuron, 18 or 36 g ai/ha halosulfuron-methyl, 18 g ai/ha nicosulfuron, or 280 g ai/ha dicamba controlled giant foxtail at least 89%, common lambsquarters at least 96% and, with the exception of the nicosulfuron combination, controlled common ragweed at least 88%. Rimsulfuron plus thifensulfuron-methyl tank-mixed with flumetsulam (26 g ai/ha) plus clopyralid (69 g ai/ha) plus 2,4-D (140 g ai/ha), atrazine (560 g ai/ha), 2,4-D (280 g/ha), or dicamba (308 g/ha) plus atrazine (588 g/ha) reduced the control of giant foxtail to less than 78% 26 d after treatment (DAT). Corn injury was less than 12% from rimsulfuron plus thifensulfuron-methyl and from mixtures of rimsulfuron plus thifensulfuron-methyl with other herbicides except when rimsulfuron plus thifensulfuron-methyl was mixed with flumetsulam plus clopyralid plus 2,4-D. This combination injured corn 26%. In these studies the appropriate tank-mix partners for rimsulfuron plus thifensulfuron-methyl were primisulfuron, CGA-152005 plus primisulfuron, and halosufluron-methyl.

Limited information exists on the tolerance of processing tomato to postemergence (POST) application of thifensulfuron-methyl. The tolerance of 13 processing tomato varieties, ‘CC337’, ‘H9144’, ‘H9314’, ‘H9478’, ‘H9492’, ‘H9553’, ‘H9909’, ‘N1069’, ‘N1082’, ‘N1480E’, ‘N1480L’, ‘N1522’, and ‘PETO696’, to POST applications of thifensulfuron-methyl at the maximum use rate (6 g ai/ha) and twice the maximum use rate (12 g/ha) for soybean was evaluated at two Ontario locations in 2001 and 2002. At 7 days after treatment (DAT), thifensulfuron applied POST caused 0.2 to 1% visible injury to CC337, H9144, N1082, N1522, and PETO696 at the high rate. H9553, H9909, N1069, and N1480E were the most sensitive to POST thifensulfuron-methyl, with visible injury ranging from 1 to 6% at the high rate. There was no visible injury to H9314, H9478, H9492, or N1480L at either application rate of thifensulfuron-methyl. By 28 DAT, no visible injury was noted to any variety, except for H9909, N1069, and N1480L, which showed minimal (<2%) visible injury. There were no adverse effects on shoot dry weight and marketable yield for any variety at either rate. Although thifensulfuron-methyl applied POST caused minimal and transient injury to the varieties tested, more tolerance trials with other fresh and processing tomato varieties are required to confirm these initial results.

Greenhouse and field studies were conducted to evaluate bell pepper tolerance to the sulfonylurea herbicides imazosulfuron and thifensulfuron-methyl. Imazosulfuron was applied at 56, 112, 224, 336, or 448 g ai ha−1. Thifensulfuron-methyl was applied at 2.6, 5.3, 10.5, 21.0, or 31.6 g ai ha−1. In the greenhouse over 2 yr, bell pepper injury due to imazosulfuron POST ranged from 12 to 27%. Reductions in plant height and numbers of nodes, buds, flowers, and fruits were generally minor or not observed. Injury from thifensulfuron-methyl POST ranged from 40 to 60% in the greenhouse. Similar trends were observed for leaf chlorosis and distortion. Thifensulfuron-methyl tended to decrease numbers of buds, flowers, and fruits in the greenhouse. In the field at three sites, bell pepper injury due to imazosulfuron applied POST-directed (POST-DIR) was less than 10% at all rating times, and height and yield were not affected. Total and marketable yield averaged 40,300 and 35,810 kg ha−1, respectively, across environments and years. Bell pepper injury from thifensulfuron-methyl applied POST-DIR in the field was less than 20% with all rates and less than 10% when rates less than 10.6 g ai ha−1 thifensulfuron-methyl were applied. Bell pepper stand (plants ha−1) or height was not affected by thifensulfuron-methyl. Thifensulfuron-methyl did not affect total bell pepper yield (39,310 kg ha−1 averaged across environments); however, reductions in Fancy grade yield were observed. No. 1 and cull yield grades tended to increase with increasing thifensulfuron-methyl rate, apparently compensating for lost Fancy yield.

Resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was identified in a population of common waterhemp that had been treated with acifluorfen for several years. The protox-resistant biotype of common waterhemp was approximately 34, 82, 8, and 4 times more resistant than a susceptible common waterhemp biotype to acifluorfen, lactofen, fomesafen, and sulfentrazone, respectively. The resistant biotype also showed a high level of resistance to acetolactate synthase–inhibiting herbicides thifensulfuron and imazethapyr but not to glyphosate or paraquat. An organophosphate insecticide was applied with acifluorfen or lactofen to determine if metabolism could be the mechanism of resistance. No differences were observed between resistant plants treated with an organophosphate plus a protox-inhibiting herbicide and plants treated with a protox-inhibiting herbicide alone.

Field studies were conducted to evaluate POST herbicides with adjuvants for the control of three-cornered jack in winter wheat. The herbicides evaluated were fluroxypyr 9.7% w/w + MCPA 38.8% w/w (formulated mixture [450 g ai ha−1]), carfentrazone-ethyl (20 g ai ha−1), bromoxynil 26.8% w/w + MCPA 40.0% w/w (formulated mixture [450 g ai ha−1]), thifensulfuron-methyl (75 g ai ha−1), and tribenuron-methyl (75 g ai ha−1), applied alone or tank mixed with the adjuvants alkyl ether sulfate sodium salt (625 mL ha−1) or fatty alcohol ethoxylate (375 mL ha−1). The addition of adjuvants to carfentrazone-ethyl resulted in > 94% control of three-cornered jack. Both adjuvants enhanced the efficacy of all herbicides for control of three-cornered jack, except thifensulfuron-methyl. However, a maximum increase in phytotoxicity on three-cornered jack was achieved with the addition of either adjuvant to tribenuron-methyl compared with herbicides used alone. Bromoxynil + MCPA and carfentrazone-ethyl gave maximum wheat yield and yield components.

Field experiments were conducted at the Ohio Agricultural Research and Development Center in Wooster, OH, in 2005, 2006, and 2007 to evaluate the tolerance of eight tomato varieties to thifensulfuron-methyl and POST control of broadleaf weeds. Herbicide treatments included thifensulfuron-methyl at 0, 6, and 12 g ai ha−1. In 2005, significant injury was observed in variety TR122244 at 1 and 3 wk after treatment (WAT). The highest crop injury in 2005 was 38% at 1 WAT for variety TR122244. However, this variety experienced a conflicting effect on crop marketable yield when treated with the low and high rates of thifensulfuron-methyl in 2005. Variety TR122244 had the highest crop injury, yet produced the highest marketable yield when treated with either rate of thifensulfuron-methyl. At 3 WAT in 2005, significant injury occurred in variety 11111120, with 13% injury recorded for both the high and low rates of thifensulfuron-methyl. No significant injury resulted from either rate of thifensulfuron-methyl at 1, 3, or 6 WAT in 2006 or 2007. However, in 2006 a significant marketable yield reduction was observed for variety 97045116 when treated with the high rate of thifensulfuron-methyl. No varieties experienced significant marketable yield effects or injury when treated with either rate of thifensulfuron-methyl in 2007. Registration of thifensulfuron-methyl herbicide is not recommended at this time because of the potential for crop stunting and yield reduction in certain tomato varieties.

Deciding on the most efficacious PRE and POST herbicide options and their ideal application timing can be challenging for soybean producers. Climatic events during the 14 d before and after herbicide application can further complicate decisions because of their influence on herbicide effectiveness. Nine field trials were conducted at three locations in southwestern Ontario from 2003 to 2006, to determine the most effective PRE and POST soybean herbicides for control of common lambsquarters, common ragweed, green foxtail, and redroot pigweed. When precipitation was low at least 7 d before and after herbicide application weed control was reduced in treatments that included imazethapyr (PRE or POST) or flumetsulam/S-metolachlor (a premix formulation) (PRE). Cumulative precipitation during the 12 d after PRE application that exceeded the monthly average by at least 60% reduced common lambsquarters control when metribuzin was applied and green foxtail control when imazethapyr was applied. Delaying application of imazethapyr + bentazon to a later soybean growth stage decreased control of common lambsquarters and green foxtail; however, environmental conditions appeared to influence these results. Precipitation on the day of application decreased control of common ragweed and redroot pigweed more with quizalofop-p-ethyl + thifensulfuron-methyl + bentazon compared with imazethapyr + bentazon. Soybean yield varied among POST herbicide treatments because of reduced weed control. This research confirms that environmental conditions pre- and postapplication, as well as application timing, influence herbicide efficacy and should be considered by growers when selecting an herbicide program.

Glyphosate-resistant common waterhemp is a difficult-to-control annual broadleaf weed that has become a serious management challenge for growers in Nebraska and other states in the United States. The objectives of this study were to confirm glyphosate-resistant common waterhemp in Nebraska by quantifying level of resistance in a dose-response study, and to determine the sensitivity and efficacy of POST soybean herbicides for controlling suspected glyphosate-resistant common waterhemp biotypes. Seeds of suspected glyphosate-resistant common waterhemp biotypes were collected from seven eastern Nebraska counties. Greenhouse dose-response experiments were conducted to evaluate the response of common waterhemp biotypes to nine rates of glyphosate (0 to 16×). Common waterhemp biotypes were 3- to 39-fold resistant to glyphosate depending on the biotype being investigated and the susceptible biotype used for comparison. Results of the POST soybean herbicides efficacy experiment suggested that glyphosate-resistant biotypes, except a biotype from Pawnee County, had reduced sensitivity to acetolactate synthase (ALS)–inhibiting herbicides (chlorimuron-ethyl, imazamox, imazaquin, imazethapyr, and thifensulfuron-methyl). Glufosinate and protoporphyrinogen oxidase (PPO)–inhibiting herbicides (acifluorfen, fluthiacet-methyl, fomesafen, and lactofen) provided ≥ 80% control of glyphosate-resistant common waterhemp at 21 d after treatment (DAT). This study confirmed the first occurrence of glyphosate-resistant common waterhemp in Nebraska, and also revealed reduced sensitivity to ALS-inhibiting herbicides in most of the biotypes tested in this study.

The evolution of glyphosate and acetolactate synthase (ALS) inhibitor-resistant common waterhemp in the Midwestern United States has reduced the number of effective POST herbicide options for management of this problem weed in glyphosate-resistant soybean. Moreover, common waterhemp emerges throughout the crop growing season, justifying the need to evaluate herbicide programs that provide season-long control. The objectives of this study were to compare POST-only and PRE followed by (fb) POST herbicide programs for control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean. Field experiments were conducted in 2013 and 2014 in Dodge County, NE, in a field infested with glyphosate-resistant common waterhemp. Programs containing PRE herbicides resulted in ≥83% control of common waterhemp and densities of ≤35 plantsm–2 at 21 d after PRE (DAPRE). Post-only herbicide programs resulted in <70% control and densities of 107 to 215 plants m–2 at 14 d after early-POST (DAEPOST) treatment. PRE fb POST herbicide programs, including saflufenacil plus imazethapyr plus dimethenamid-P, sulfentrazone plus cloransulam, or S-metolachlor plus metribuzin, fb fomesafen plus glyphosate; S-metolachlor plus fomesafen fb acifluorfen plus glyphosate resulted in >90% control of glyphosate-resistant common waterhemp throughout the growing season, reduced density to ≤7plantsm–2, ≥92% biomass reduction, and soybean yield >2,200kg ha–1. Averaged across herbicide programs, common waterhemp control was 84%, and density was 15 plants m–2 with PRE fb POST herbicide programs compared with 42% control, and density of 101 plants m–2 with POST-only herbicide programs at harvest. Results of this study indicated that PRE fb POST herbicide programs with effective modes of action exist for season-long control of glyphosate-resistant common waterhemp in glyphosate-resistant soybean.

In a repeated multi-year study, mother potato plants were exposed to herbicides at rates that simulated off-target application, such as through tank contamination. Following exposure of mother plants to herbicides, seed from mother plants was planted in the following growing season and crop growth, yield and tuber quality were quantified. Visual injury from herbicides was observed both in the mother plant and daughter tuber growing seasons and occasional impacts on tuber yield were noted. However, an inconsistent relationship was observed for herbicide related injury and tuber yield reductions of mother potato plants with daughter tuber growth and yield. The lack of consistency in the relationship between visual potato injury in the mother plant production and adverse daughter tuber growth and yield in the following year challenges traditional crop scouting as a tool to predict off-target herbicide risk near seed potato production.