A 4-yr field study was conducted near Grassrange, MT to determine the effects of single and repetitive picloram treatments for leafy spurge control in a native pasture. Single applications of picloram at 0.28, 0.56, 0.84, and 1.12 kg ae ha–1 averaged 0, 5, 22, and 61% leafy spurge shoot control 3 yr after treatment. Only the single applications of picloram at 1.68 and 2.24 kg ha–1 maintained leafy spurge control above 80%. A retreatment with 0.56 kg ha–1 picloram was required to maintain effective control for 3 yr when less than 1.68 kg ha–1 was applied. Leafy spurge canopy cover in the 1.68 and 2.24 kg ha–1 treatments averaged 14 and 6% 3 yr after treatment; however, all other single applications required retreatment.

Field studies were conducted over four years to determine sugarcane response to clomazone applied POST at 1.1 and 2.2 kg ai/ha. Sugarcane leaves present when clomazone was applied were chlorotic 2 WAT. Injury 4 WAT ranged from 0 to 38% following single applications in March and April. Chlorosis 4 wk after the May application of a March plus May sequential treatment was only greater than for the single March application in 1992. The number of harvestable sugarcane stalks following treatments with clomazone was intermediate between those produced with standard applications of either metribuzin at 2.6 kg ai/ha (least injurious) or terbacil as a single treatment at 1.8 kg ai/ha in March and April or as a 1.8 plus 0.9 kg/ha March plus May sequential treatment. Sugar recovery as an average of all herbicide treatments was lower for the sequential applications than for the single applications. Averaged over single and sequential treatments, theoretically recoverable sugar levels with clomazone at both rates was intermediate between the recoveries obtained with standard applications of metribuzin (highest) and terbacil. Gross cane and sugar yields following all applications of clomazone at 1.1 kg/ha and following single applications of clomazone at 2.2 kg/ha in March and April were similar to the metribuzin standard. Sugar yields following the sequential treatment of clomazone at 2.2 kg/ha, although lower than the metribuzin standard, were similar to the standard terbacil sequential treatment.

Sweet corn tolerance to nicosulfuron as affected by interactions between nicosulfuron applied postemergence (POST), sweet corn hybrid, and rootworm insecticide applied at planting was determined in 1992 and 1993 field experiments. Sweet corn vigor was reduced as nicosulfuron rate increased from 35 to 140 g ai/ha. Sweet corn vigor was reduced 4% more by nicosulfuron with oil emulsifier mixture than nicosulfuron with non-ionic surfactant one week after treatment (WAT). Adjuvant selection did not influence nicosulfuron injury to sweet corn 2 WAT. Nicosulfuron applied postemergence directed (PDIR) caused less sweet corn injury than nicosulfuron applied broadcast POST. ‘Jubilee’ sweet corn was more sensitive to nicosulfuron and insecticide treatments than ‘Excellency’ or ‘Green Giant 40.’ Nicosulfuron reduced sweet corn vigor twice as much when terbufos was applied at planting compared to no insecticide at planting. Neither chlorpyrifos or chlorethoxyfos at planting increased sweet corn injury due to nicosulfuron compared to no insecticide. Excellency and Green Giant 40 yields were not reduced by any treatment. Yields were reduced only when nicosulfuron was applied to Jubilee treated with terbufos. Jubilee yield reduction from nicosulfuron and terbufos was prevented by applying nicosulfuron PDIR.

Field studies were conducted for 3 yr to evaluate the persistence of metolachlor and alachlor applied to ‘Centennial’ soybean and to determine their residual effect on ‘Mars' rice. At labeled use rates of metolachlor at 2.8 kg ai/ha and alachlor at 3.9 kg ai/ha, soil residue levels in the fall 5 months after application on Crowley and Midland silt loam soils averaged 0.04 and 0.05 ppmw, respectively. Metolachlor fall soil residues averaged 3.5 times higher when applied at 5.6 and 11.2 kg/ha compared to 2.8 kg/ha, but residues for labeled and double rates of alachlor were similar. In the spring 9 months after herbicide application, soil residues averaged over years did not exceed 0.06 ppmw. The 3-yr rice yields were not affected by residual metolachlor or alachlor.

Preplant control of mannagrass was greater than 90% with clethodim, glyphosate, sethoxydim, and sulfosate. Glyphosate at 0.5 to 1.0 kg ai/ha controlled mannagrass greater than 97%, and was not increased with any adjuvant. Fenoxaprop applied POST controlled mannagrass 97% but injured rice 33%. Except for fenoxaprop-ethyl, all POST treatments increased rice yields at least 1560 kg/ha more than the non-treated check. Southern watergrass was controlled 79 and 89% with 1.0 kg ai/ha glyphosate and 4.5 kg ai/ha sulfosate, respectively, while control was less than 55% with other herbicides.

Greenhouse and growth chamber experiments were conducted to evaluate primisulfuron phytotoxicity to downy brome (Bromus tectorum) and Kentucky bluegrass (Poa pratensis) as a function of herbicide placement, adjuvants, and environmental conditions. Primisulfuron rates needed to produce GR50 (50% growth reduction) values were 0.97 ± 0.57 and 8.07 ± 1.85 g/ha for downy brome and Kentucky bluegrass, respectively. Primisulfuron was applied to downy brome and Kentucky bluegrass at three placement sites: foliar, soil, and foliar plus soil. Foliar or foliar plus soil applications were more effective at reducing downy brome dry weights than the soil application of primisulfuron, whereas Kentucky bluegrass was injured more from the soil or foliar plus soil applications than from the foliar application of primisulfuron. Primisulfuron at 5 g/ha applied alone reduced downy brome dry weights by 5%, whereas when an adjuvant was added, dry weights were reduced by 52 to 83%. Primisulfuron was more phytotoxic to downy brome at alternating temperatures of 8 to 16 C and 16 to 24 C than at 0 to 8 C. Phytotoxicity of primisulfuron was less when downy brome plants were stressed for soil moisture after herbicide treatments than when the plants were not stressed or only stressed before treatment.

A field experiment was conducted over a 2-yr period to determine the effects of reduced PRE herbicide rates on large crabgrass infestation in six tall fescue cultivars. With the exception of oryzalin and benefin plus oryzalin in 1993, there was no cultivar by herbicide interaction for large crabgrass infestation when final ratings were made in 1993 and 1994. This interaction was caused by moderate to severe turfgrass injury that thinned the turf. When cultivars were disregarded, prodiamine was the only herbicide applied at one-third recommended rate in 1993 that effectively suppressed large crabgrass for the full season. Prodiamine and dithiopyr were the only PRE herbicides applied at one-third recommended rates for two consecutive years that effectively suppressed large crabgrass in 1994. Two-thirds recommended rate was needed for two consecutive years for oxadiazon, pendimethalin, oryzalin, benefin plus oryzalin, and benefin plus trifluralin to maintain optimum large crabgrass suppression in 1994.

Glyphosate effectively kills duncecap and tall larkspur on mountain rangelands but it is nonselective and kills all other vegetation it contacts. Two selective application methods to treat individual plants were compared to demonstrate their efficacy in controlling larkspur and their effect on associated plant species: (1) spot spray with glyphosate concentration at 2% product solution (0.8% ai); (2) hand held wiper applicator with glyphosate concentration at 33% production solution (13.5% ai). The two methods were equally effective in killing most of the larkspur plants, but the sprayer applicator was more rapid and easier to apply. Neither method adversely affected foliar cover of associated perennial species. Glyphosate must be applied to the entire plant to ensure its mortality.

Field studies were conducted in Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, and Tennessee during 2010 and 2011 to determine the effect of glufosinate application rate on LibertyLink and WideStrike cotton. Glufosinate was applied in a single application (three-leaf cotton) or sequential application (three-leaf followed by eight-leaf cotton) at 0.6, 1.2, 1.8, and 2.4 kg ai ha−1. Glufosinate application rate did not affect visual injury or growth parameters measured in LibertyLink cotton. No differences in LibertyLink cotton yield were observed because of glufosinate application rate; however, LibertyLink cotton treated with glufosinate yielded slightly more cotton than the nontreated check. Visual estimates of injury to WideStrike cotton increased with each increase in glufosinate application rate. However, the injury was transient, and by 28 d after the eight-leaf application, no differences in injury were observed. WideStrike cotton growth was adversely affected during the growing season following glufosinate application at rates of 1.2 kg ha−1 and greater; however, cotton height and total nodes were unaffected by glufosinate application rate at the end of the season. WideStrike cotton maturity was delayed, and yields were reduced following glufosinate application at rates of 1.2 kg ha−1 and above. Fiber quality of LibertyLink and WideStrike cotton was unaffected by glufosinate application rate. These data indicate that glufosinate may be applied to WideStrike cotton at rates of 0.6 kg ha−1 without inhibiting cotton growth, development, or yield. Given the lack of injury or yield reduction following glufosinate application to LibertyLink cotton, these cultivars possess robust resistance to glufosinate. Growers are urged to be cautious when increasing glufosinate application rates to increase control of glyphosate-resistant Palmer amaranth in WideStrike cotton. However, glufosinate application rates may be increased to maximum labeled rates when making applications to LibertyLink cotton without fear of reducing cotton growth, development, or yield.

Silvery threadmoss naturally reproduces through spore and bulbil production, both of which have potential to be controlled prior to establishment. Studies have not evaluated effects of turf protection products on moss protonema or gametophyte growth from spores or bulbils; consequently, most moss is controlled POST on putting greens. Initial studies were performed to determine the optimal growth temperature for spores and bulbils in sterile culture. Protonemata from spores grew optimally at 29.5 C and gametophytes from bulbils grew optimally at 22.5 C. Three subsequent in vitro studies were conducted to evaluate effects of turf protection products on moss development from spores or bulbils in axenic culture at a constant 24 C. Carfentrazone, which effectively controls mature silvery threadmoss gametophytes POST, also reduced green cover of moss protonemata and gametophyte production from spores and bulbils. All combinations with carfentrazone reduced area under the progress curve (AUPC) for green cover of moss for both spores and bulbils by 80% or more by 3 wk after treatment. Sulfentrazone, oxyfluorfen, oxadiazon, saflufenacil, flumioxazin, and pyraflufen-ethyl reduced AUPC of moss equivalent to carfentrazone for both propagule types. The two fosetyl-Al products, phosphite, and mineral oil caused an increase in silvery threadmoss cover between 22 and 113% of the nontreated for spores; however, only methiozolin positively influenced AUPC (90.2%) compared to the nontreated for bulbils. Though silvery threadmoss is typically targeted POST on putting greens, there are products that can provide PRE control, including the industry standard of carfentrazone. These data suggest that differences may occur between turf protection products in their ability to suppress silvery threadmoss establishment from spores or bulbils.

Aminocyclopyrachlor (AMCP) is a newly developed synthetic auxin herbicide for broadleaf weed control in turfgrass systems. AMCP has been observed to undergo rapid photodecomposition in shallow water when exposed to sunlight. Most herbicide applications on golf courses occur during the morning when dew is still present on the turfgrass canopy. These conditions could result in efficacy loss if photolysis occurred while AMCP is suspended in dew droplets. Research was conducted to determine the effect of ambient moisture on AMCP efficacy. AMCP (79 and 105 g ae ha−1), aminopyralid (280 g ae ha −1), and two AMCP granular formulations (84 g ha−1) were applied to dew-covered (WET) and dew-excluded (DRY) ‘Tifway' bermudagrass plots. Herbicide treatments applied to WET plots had greater visually rated bermudagrass injury than respective treatments applied to DRY plots at 7 and 21 d after treatment (DAT), with the exception of aminopyralid at 21 DAT. Normalized difference vegetative index on turfgrass quality complemented visual ratings, indicating greater turfgrass quality reductions when applied to WET vs. DRY plots. These results indicate that AMCP applications made to dew-covered turfgrass can increase herbicidal efficacy, and no significant losses due to photodegradation were observed.

Horseweed is a competitive summer or winter annual weed that produces up to 230,000 small seeds per plant that are capable of traveling more than 500 km via wind. Giant ragweed is a tall, highly competitive summer annual weed. Glyphosate-resistant (GR) horseweed and GR giant ragweed pose significant challenges for producers in the United States and Ontario, Canada. It is thought that an integrated weed management (IWM) system involving herbicide rotation is required to control GR biotypes. Halauxifen-methyl is a new selective broadleaf POST herbicide registered for use in cereal crops; there is limited information on its efficacy on horseweed and giant ragweed. The purpose of this research was to determine the efficacy of halauxifen-methyl applied POST, alone and in a tank mix, for the control of GR horseweed and GR giant ragweed in wheat across southwestern Ontario. For each weed species, an efficacy study consisting of six field experiments was conducted over a 2-yr period (2018, 2019). At 8 wk after application (WAA), halauxifen-methyl, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, 2,4-D ester, clopyralid, and pyrasulfotole/bromoxynil + ammonium sulfate controlled GR horseweed >95%. Fluroxypyr and MCPA provided only 86% and 37% control of GR horseweed, respectively. At 8 WAA, fluroxypyr, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, fluroxypyr/halauxifen-methyl + MCPA EHE + pyroxsulam, 2,4-D ester, clopyralid, and thifensulfuron/tribenuron + fluroxypyr + MCPA ester controlled GR giant ragweed 87%, 88%, 90%, 94%, 96%, 96%, 98%, and 93%, respectively. Halauxifen-methyl and pyroxsulam provided only 45% and 28% control of GR giant ragweed, respectively. Halauxifen-methyl applied alone POST in the spring controlled GR horseweed but not GR giant ragweed in winter wheat.

Weeds are difficult to control in potted tropical ornamentals, especially when plants are kept for extended time periods at a nursery. Management is complicated by the lack of tolerance data for many tropical species. Experiments were conducted in 2015, 2016, and 2017 at the Gulf Coast Research and Education Center in Balm, FL, to evaluate tolerance of stromanthe, croton, philodendron, arbicola, cordyline, ixora, plumbago, allamanda, bird-of-paradise, firebush, and hibiscus to granular applications of indaziflam, flumioxazin, pendimethalin + oxyfluorfen, pendimethalin + dimethenamid-P, trifluralin + oxyfluorfen + isoxaben, and trifluralin + isoxaben, and liquid applications of prodiamine + isoxaben and dimethenamid-P. Indaziflam, pendimethalin + oxyfluorfen, and trifluralin + oxyfluorfen + isoxabin were safe for use on all evaluated ornamentals except stromanthe. Dimethenamid-P and pendimethalin + oxyfluorfen were safe on all evaluated ornamentals except allamanda. Flumioxazin damaged philodendron and bird-of-paradise but was safe on all other ornamentals tested. Trifluralin + isoxaben and prodiamine + isoxaben were safe on hibiscus, firebush, and bird-of-paradise, but prodiamine + isoxaben damaged allamanda. We have identified multiple PRE herbicides that can safely be used on multiple tropical ornamentals grown in containers.

Residual herbicides are routinely applied to control troublesome weeds in pumpkin production. Fluridone and acetochlor, Groups 12 and 15 herbicides, respectively, provide broad-spectrum PRE weed control. Field research was conducted in Virginia and New Jersey to evaluate pumpkin tolerance and weed control to PRE herbicides. Treatments consisted of fomesafen at two rates, ethalfluralin, clomazone, halosulfuron, fluridone, S-metolachlor, acetochlor emulsifiable concentrate (EC), acetochlor microencapsulated (ME), and no herbicide. At one site, fluridone, acetochlor EC, acetochlor ME, and halosulfuron injured pumpkin 81%, 39%, 34%, and 35%, respectively, at 14 d after planting (DAP); crop injury at the second site was 40%, 8%, 19%, and 33%, respectively. Differences in injury between the two sites may have been due to the amount and timing of rainfall after herbicides were applied. Fluridone provided 91% control of ivyleaf morningglory and 100% control of common ragweed at 28 DAP. Acetochlor EC controlled redroot pigweed 100%. Pumpkin treated with S-metolachlor produced the most yield (10,764 fruits ha–1) despite broadcasting over the planted row; labeling requires a directed application to row-middles. A separate study specifically evaluated fluridone applied PRE at 42, 84, 126, 168, 252, 336, and 672 g ai ha–1. Fluridone resulted in pumpkin injury ≥95% when applied at rates of ≥168 g ai ha–1; significant yield loss was noted when the herbicide was applied at rates >42 g ai ha–1. We concluded that fluridone and acetochlor formulations are unacceptable candidates for pumpkin production.

Since the release of dicamba-tolerant cotton in 2016, preplant and POST applications of dicamba to control glyphosate-resistant Palmer amaranth have increased. With the increase in area treated with dicamba, the risk of off-target movement to nontarget crops has increased. A field study was conducted at the Texas Tech University New Deal Research Farm equipped with subsurface drip irrigation in 2017 and 2018 to evaluate non-dicamba tolerant cotton response to dicamba when applied at four crop growth stages [first square (FS) + 2 wk, first bloom (FB), FB + 2 wk, and FB + 5 wk]. Dicamba at 0.56 (1×), 0.056 (1/10×), 0.0112 (1/50×), 0.0056 (1/100×), and 0.00112 (1/500×) kg ae ha−1 was applied to ‘FM 1830GLT’ cotton. When applications were made at FS + 2 wk, a shift in boll nodal position was apparent following dicamba at the 1/50× rate in 2017 and at 1/10× in 2018 compared to the nontreated control (NTC). A shift in boll distribution from the 1/50× rate of dicamba was apparent at FB in 2017, but not in 2018. Dicamba applied at the 1× rate at FB + 2 wk resulted in reduced boll numbers. No change in boll number or boll position was apparent following any dicamba rate when applied at FB + 5 wk in both years. Dicamba applied at 1/500×, 1/100×, and 1/50× rates at all timings did not affect yield relative to the NTC. When dicamba was applied at the 1/10× rate, the greatest yield loss was observed at FS + 2 wk followed by FB and FB + 2 wk. Micronaire increased following dicamba applied at 1/10× at FS + 2 wk, FB, and FB + 2 wk in 2017. In 2018, micronaire decreased following dicamba applied at 1/10× at FB + 5 wk.

Glyphosate-resistant (GR) horseweed is a problematic weed for Michigan soybean growers. Additionally, rosette- and upright-horseweed growth types have been observed co-emerging during mid- to late summer in several Michigan fields. In the greenhouse, shade levels from 35% to 92% reduced rosette- and upright-horseweed biomass 31% to 99% compared with the upright growth type grown under 0% shade. Greater reductions in biomass occurred under 69% and 92% shade. Thus, increased shading by planting in narrow rows and/or planting green into cereal rye may improve horseweed suppression. A field experiment conducted over 3 site-years compared the effect of fall-planted cereal rye terminated with glyphosate 1 wk after planting (WAP; planting green) with a preemergence residual herbicide program (glyphosate + 2,4-D + flumioxazin + metribuzin) on horseweed control in soybean planted in three row widths (19, 38, and 76 cm). Planting green or applying a residual herbicide program across all row widths reduced horseweed biomass 86% to 91% and 95% to 99%, respectively, compared with soybean planted with no cover in 76-cm rows, 4 to 6 WAP. At soybean harvest, when a noneffective postemergence herbicide (glyphosate) was applied, horseweed biomass was 42% and 81% lower by planting green or applying a residual-herbicide program compared with no cover, respectively. Similarly, planting soybean in 19-cm rows reduced horseweed biomass compared with 38- and 76-cm rows. When an effective postemergence program was applied, similar horseweed biomass reductions were observed by planting green or applying a residual herbicide across all row widths. Additionally, soybean yield and economic returns were similar between planting green and applying a residual herbicide in 1 of 2 site-years. Integrating planting green and an effective postemergence herbicide program offers an alternative horseweed management strategy to applying a residual preemergence herbicide program.

Junglerice has become a major weed in Tennessee cotton and soybean fields. Glyphosate has been relied on to control these accessions over the past two decades, but in recent years cotton and soybean producers have reported junglerice escapes after glyphosate + dicamba and/or clethodim applications. In the growing seasons of 2018 and 2019, a survey was conducted of weed escapes in dicamba-resistant (DR) crops. Junglerice was the most prevalent weed escape in these DR (Roundup Ready Xtend®) cotton and soybean fields in both years of the study. In 2018 and 2019, junglerice was found 76% and 64% of the time in DR cotton and soybean fields, respectively. Progeny from junglerice seeds collected during this survey was screened for glyphosate and clethodim resistance. Seventy percent of the junglerice accessions tested had an effective relative resistance factor to glyphosate of 3.1 to 8.5. In all, 13% of the junglerice accessions could no longer be effectively controlled with glyphosate. This research also showed that all sampled accessions could still be controlled with clethodim in a greenhouse environment, but less control was observed in the field. These data also suggest that another cause for the poor junglerice control is dicamba antagonism of glyphosate and clethodim activity.

Two field studies were conducted in Louisiana to determine the impact of Nealley’s sprangletop on rough rice yield under multiple environments in 2014, 2015, and 2016. The first study evaluated optimal timings of Nealley’s sprangletop removal for optimizing rough rice yields. The second study evaluated the impact of Nealley’s sprangletop densities on rough rice yield. Nealley’s sprangletop was removed with applications of fenoxaprop at 122 g ai ha–1 at 7, 14, 21, 28, 35, and 42 d after emergence (DAE). Nealley’s sprangletop removal at 7 and 14 DAE resulted in higher rough rice yields of 7,880 and 6,960 kg ha–1, respectively, when compared with the rice from the season-long Nealley’s sprangletop competition with a 6,040 kg ha-1 yield. Delaying herbicide application from 7 DAE to 42 DAE resulted in a yield loss of 1,740 kg ha–1. Over the 35-d delay in application, rough rice yield loss from Nealley’s sprangletop interference was equivalent to 50 kg ha–1 d–1. Nealley’s sprangletop densities were established at 1, 3, 7, 13, and 26 plants m–2 by transplanting Nealley’s sprangletop when rice reached the one- to two-leaf stage. At Nealley’s sprangletop densities of 1 to 26 plants m–2, rough rice yields were reduced 10 to 270 kg ha–1, compared with the rice from weed-free plots. Based on regression analysis, Nealley’s sprangletop densities of 1, 35, 70, and 450 plants m–2 reduced rough rice yield 0.14%, 5%, 10%, and 50%, respectively.

Research using the critical period for weed control (CPWC) has shown that high-yielding cotton crops are very sensitive to competition from grasses and large broadleaf weeds, but the CPWC has not been defined for smaller broadleaf weeds in Australian cotton. Field studies were conducted over five seasons from 2003 to 2015 to determine the CPWC for smaller broadleaf weeds, using mungbean as a mimic weed. Mungbean was planted at densities of 1, 3, 6, 15, 30, and 60 plants m−2 with or after cotton emergence and added and removed at approximately 0, 150, 300, 450, 600, 750, and 900 degree days of crop growth (GDD). Mungbean competed strongly with cotton, with season-long interference; 60 mungbean plants m−2 resulted in an 84% reduction in cotton yield. A dynamic CPWC function was developed for densities of 1 to 60 mungbean plants m−2 using extended Gompertz and exponential curves including weed density as a covariate. Using a 1% yield-loss threshold, the CPWC defined by these curves extended for the full growing season of the crop at all weed densities. The minimum yield loss from a single weed control input was 35% at the highest weed density of 60 mungbean plants m−2. The relationship for the critical time of weed removal was further improved by substituting weed biomass for weed density in the relationship.

Sugarbeet, grown for biofuel, is being considered as an alternate cool-season crop in the southeastern U.S. coastal plain. Typically, the crop would be seeded in the autumn, then grow through the winter and be harvested the following spring. Labels for herbicides registered for use on sugarbeet grown in the traditional sugarbeet production regions do not list any of the cool-season weeds common in the southeastern United States. Field trials were initiated near Ty Ty, GA, to evaluate all possible combinations of ethofumesate applied PRE, phenmedipham+desmedipham applied POST, clopyralid POST, and triflusulfuron POST for cool-season weed control in sugarbeet. Phenmedipham+desmedipham alone and in combination with clopyralid and/or triflusulfuron effectively controlled cutleaf eveningprimrose, lesser swinecress, henbit, and corn spurry when applied to seedling weeds. Ethofumesate PRE alone was not as effective in controlling cool-season weeds compared to treatments containing phenmedipham+desmedipham POST. However, ethofumesate PRE applied sequentially with phenmedipham+desmedipham POST improved weed control consistency. Clopyralid and/or triflusulfuron alone did not adequately control cutleaf eveningprimrose. Triflusulfuron alone effectively controlled wild radish. In the 2013–2014 and 2014–2015 seasons, December-applied POST herbicides did not injure sugarbeet. However, in the 2015–2016 season POST herbicides were applied in late October. On the day of treatment, the maximum temperature was 25.4 C, which exceeded the established upper temperature limit of 22 C for safe application of phenmedipham+desmedipham, and sugarbeet plants were severely injured. In the southeastern United States, temperatures frequently exceed 22 C in early autumn, which may limit phenmedipham+desmedipham use for controlling troublesome cool-season weeds of sugarbeet in the region. Weed control options need to be expanded to compensate for this limitation.