Currently, a limited number of herbicides is available to treat water-seeded rice in California, with widespread resistance to most of those herbicides. Because no resistant grasses showed resistance to pendimethalin, a series of studies were conducted to evaluate water-seeded rice response to pendimethalin. In a field study conducted at the Rice Experiment Station at Biggs, California, in 2020 and 2021, three pendimethalin formulations, a granule (GR), emulsifiable concentrate (EC), and capsule suspension (CS), were applied at 1.1, 2.3, and 3.4 kg ai ha−1 rates, and at 5, 10, and 15 d after seeding onto water-seeded rice. In addition, a greenhouse study was conducted to examine the response of five common California rice cultivars to GR and CS formulation applications. Echinochloa control levels were reduced at 15 d after seeding after use of EC and CS formulations compared with earlier timings. In both years, rice grain yields were increased by 3,014 kg ha−1 after application of pendimethalin at 3.4 kg ai ha−1 when applied at 15 d after seeding compared with 5 and 10 d after seeding, and similar to 1.1 kg ai ha−1 applications. The GR and CS were safer formulations based on a reduction in injury and an increase in grain yields compared to the EC formulation. Differences in seedling vigor across cultivars appeared to incur an advantage after a pendimethalin application. However, most cultivars evaluated for stand reduction and dry biomass demonstrated tolerance to GR and CS formulation applications only after rice reached the 3-leaf stage. In contrast, an application at 1-leaf stage rice reduced stand up to 68%. Application rate, timing, and formulation are important factors to consider if the use of pendimethalin in water-seeded rice is to be pursued.

Understanding control of glyphosate-resistant (GR) Palmer amaranth with multiple herbicide sites of action, including synthetic auxins, is crucial for growers to minimize GR Palmer amaranth interference with crops. Field studies in 2013 and 2014 and a greenhouse study in 2014 were conducted in Stoneville, MS, to evaluate POST control of GR Palmer amaranth with 2,4-D alone and in mixtures with glyphosate and/or glufosinate. In the greenhouse study, control of 5- and 10-cm GR Palmer amaranth was 87% with 2,4-D at 0.84 kg ae ha−1. Dry weight reduction of GR Palmer amaranth was ≥81% with 2,4-D at 0.84 kg ha−1. In field studies, mixtures of glufosinate at 0.59 kg ai ha−1 and 2,4-D at 0.56 or 1.12 kg ae ha−1 controlled 5- to 10-cm GR Palmer amaranth 87% at 28 d after treatment (DAT). Averaged across glyphosate treatments, glufosinate applied alone applied to 5- to 10-cm GR Palmer amaranth reduced dry weight at 28 DAT to 20 g m−2 from 82 g m−2 and was comparable with that following 2,4-D applied alone at 1.12 kg ae ha−1 and mixtures of glufosinate plus 2,4-D at 0.56 and 1.12 kg ae ha−1. Mixtures of 2,4-D plus glufosinate provided ≥92% control of 15- to 20-cm GR Palmer amaranth at 28 DAT. When applied to 15- to 20-cm plants, mixtures of 2,4-D plus glufosinate reduced GR Palmer amaranth density to ≤5 plants m−2 compared with 65 plants m−2 where no 2,4-D or glufosinate was applied. Glufosinate and 2,4-D are viable control options for 5- to 10-cm or 15- to 20-cm GR Palmer amaranth. However, 2,4-D did not improve GR Palmer amaranth control when added to any herbicide mixture except glyphosate and glufosinate applied to 15- to 20-cm plants at the 28 DAT evaluation.

Six experiments were conducted in three rice fields near Harrisburg, AR in Poinsett County in 1991 and 1992 to confirm barnyardgrass resistance to propanil and to compare herbicide treatments for control of propanil-resistant barnyardgrass. In all experiments, standard treatments of thiobencarb applied delayed PRE or tank mixtures of propanil + thiobencarb applied POST controlled propanil-resistant barnyardgrass. In five of six experiments, propanil failed to control barnyardgrass at 6 to 8 kg ai/ha (three times use rates) and in three experiments it provided inconsistent control at 11 kg/ha. Emulsifiable propanil at 11 kg/ha frequently controlled resistant barnyardgrass better than the dry flowable formulation. Treatments that consistently controlled propanil-resistant barnyardgrass included propanil tank-mixed with pendimethalin or quinclorac applied POST to two-leaf grass; quinclorac applied alone delayed PRE or POST or applied POST tank-mixed with thiobencarb, pendimethalin, or a formulated mixture of molinate and propanil; a formulated mixture of propanil and molinate applied POST in tank mixtures with thiobencarb or pendimethalin; and fenoxaprop or fenoxaprop-P alone applied POST to four-leaf grass prior to flood establishment. Herbicide treatments that failed to control resistant barnyardgrass included POST applications of a formulated mixture of propanil and molinate alone and propanil in tank mixtures with bromoxynil or triclopyr. These studies confirm that barnyardgrass from several farms in Arkansas have resistance to propanil and identified treatments that control propanil-resistant barnyardgrass.

The effects of herbicide–adjuvant combinations and times of application on weed density and corn yield were determined in a 3-yr field study. At a given rate and time of application of bentazon/atrazine, Assist and Merge were equally effective adjuvants. Assist would be the adjuvant of choice for bentazon/atrazine rather than Merge because of its currently lower cost. Weed density depended on the rate and time of application of bentazon/atrazine. In general, bentazon/atrazine applied at early stages (7 d after emergence) of the development of corn seedlings or at high or intermediate rate (1.6 or 0.8 kg ai/ha) maintained low weed densities, with a relatively small range of variation over years. Delay in time (14 or 21 d after emergence) or reduction in herbicide rate (0.4 kg ai/ha) increased the risk of high weed pressure, although it was not always associated with yield loss. The best time for the application of postemergence herbicide appears to be a few days prior to the onset of the critical period of weed control.

Greenhouse and growth chamber experiments were conducted to determine the reasons for stunted growth and yield suppression of corn noticed sometimes in nicosulfuron-treated corn fields infested with heavy population of johnsongrass. Results indicated that in the absence of johnsongrass, nicosulfuron applied broadcast POST at 35 g ai ha−1 had no effect on corn. However, growth reduction of corn occurred when nicosulfuron-treated johnsongrass and corn were allowed to share the same rooting medium with their root systems intermingled. The reduction in growth was even greater when corn foliage or the soil surface were also treated with johnsongrass. The extent of growth reduction of corn growing with nicosulfuron-killed johnsongrass depended on weed density and herbicide application rate. Greater growth reductions occurred at four johnsongrass plants per pot compared to two and at a higher application rate of 100 μg nicosulfuron per plant. In general, johnsongrass killed by nicosulfuron appeared to be more phytotoxic to corn than plants killed by paraquat. Nicosulfuron provided excellent control of johnsongrass and improved corn growth by two to three times that of not controlling johnsongrass, but it could not elevate corn growth to the level obtained when johnsongrass was controlled by paraquat or in the absence of interference from johnsongrass.

A commercial fertilizer (40-0-0, N-P-K) was screened into seven particle size fractions (23, 58, 165, 465, 1,310, 3,728, or 10,606 particles/g) and coated with dithiopyr (0.345%, wt/wt), prodiamine (0.689%), oryzalin (3.28%), or oxadiazon (2.76%). Dithiopyr and oryzalin provided best southern crabgrass control with a fertilizer size of 465 particles/g or greater, whereas prodiamine controlled southern crabgrass greatest using a size fraction at least 165 particles/g. Southern crabgrass control with oxadiazon was not as dependent on particle size, with all fraction sizes of 58 or 165 particles/g or greater controlling southern crabgrass equally in 1995 or 1996, respectively.

Field studies were conducted in 2014 and 2015 at Pontotoc, MS to evaluate combinations of metam-potassium and S-metolachlor for yellow nutsedge control and sweetpotato crop response. Treatments consisted of a factorial of five metam-potassium rates (0, 149, 261, 372, and 484 kgha−1) by three S-metolachlor rates (0, 0.80, and 1.34 kgha−1). Additionally, a hand-weeded check was included for comparison. Crop injury was limited to ≤4% at 4 weeks after transplanting (WAP) and was transient. At 2 WAP yellow nutsedge control was 58, 74, and 76% in plots treated with S-metolachlor at 0, 0.80, and 1.34 kgha−1, respectively. Nutsedge control in all treatments decreased from 2 to 15 WAP. At 15 WAP, S-metolachlor at 0, 0.80, and 1.34 kg ha−1 provided 35, 68, and 70% yellow nutsedge control, respectively. Metam-potassium rate did not influence yellow nutsedge control after transplanting. Sweetpotato yields in the hand-weeded check were 4,640; 22,180; 7,180; 34,000; and 1,360 kgha−1 for jumbo, no. 1, canner, marketable, and cull grades, respectively. S-metolachlor applied at either 0.80 or 1.34 kgha−1 provided jumbo, no. 1, and marketable sweetpotato yields equivalent to the hand-weeded check. Canner and cull yields were not influenced by S-metolachlor rate. Metam-potassium rates used in the present study resulted in yields equal to or greater than the hand-weeded check.

Studies were conducted in 2008 and 2009 to determine the effect of S-metolachlor rate and application time on sweetpotato cultivar injury and storage root shape under conditions of excessive moisture at the time of application. S-metolachlor at 1.1, 2.2, or 3.4 kg ai ha−1 was applied immediately after transplanting or 2 wk after transplanting (WATP) to ‘Beauregard’, ‘Covington’, ‘DM02-180’, ‘Hatteras’, and ‘Murasaki-29’ sweetpotato. One and three d after S-metolachlor application plots received 1.9 cm rainfall or irrigation. S-metolachlor applied immediately after transplanting resulted in increased sweetpotato stunting 4 and 12 WATP, decreased no. 1 and marketable sweetpotato yields, and decreased storage root length to width ratio compared with the nontreated check. Sweetpotato stunting, no. 1 and marketable yields, and storage root length to width ratio in treatments receiving S-metolachlor 2 WATP were similar to the nontreated check. In 2008, Covington and Hattaras stunting 12 WATP was greater at 2.2 and 3.4 kg ha−1 (11 to 16%) than 1.1 kg ha−1 (1 to 2%). In 2009, S-metolachlor at 3.4 kg ha−1 was more injurious 4 WATP than 2.2 kg ha−1 and 1.1 kg ha−1. While cultivar by treatment interactions did exist, injury, yield, and storage root length to width ratio trends were similar among all cultivars used in this study.

Greenhouse studies were conducted in Raleigh, NC to determine Carolina redroot control by selected PRE and POST herbicides labeled for blueberries. Paraquat, glufosinate, glyphosate, and flumioxazin provided some Carolina redroot shoot control 7 d after POST application (DAPOST) ranging from 48 to 74%. Control 25 DAPOST was greatest for hexazinone at 2.2 kg ai ha−1 (90%) followed by glufosinate with 56% control and paraquat and terbacil each with 53% control. Control for most treatments declined between 25 and 63 DAPOST with the exception of glyphosate, which increased to 64%. Carolina redroot shoots per pot were reduced by terbacil, hexazinone at 2.2 kg ha−1, and glyphosate compared with the nontreated check 63 DAPOST. Control of Carolina redroot roots and rhizomes 63 DAPOST ranged from 7 to 68%, with the greatest control provided by terbacil (68%) and hexazinone at 2.2 kg ha−1 (64%). Terbacil and hexazinone at 2.2 kg ha−1 were the only treatments that reduced both shoot and root/rhizome dry weight compared with the nontreated check.

Field trials were conducted to evaluate imazosulfuron applied POST at 0.1, 0.2, 0.3, and 0.4 kg/ha to watermelon at the two- to four-leaf stage or to vines 30.5 cm long. At 7 d after treatment (DAT), crop injury to watermelon increased linearly for both growth stages as rate increased. The least injury to watermelon observed 7 DAT was 19 and 15%, respectively, for the two- to four-leaf and 30.5-cm growth stages treated with 0.01 kg/ha imazosulfuron. The 0.4 kg/ha imazosulfuron treatment caused the greatest watermelon injury (approximately 30%) at both application timings. Yield of watermelon treated with 0.1 and 0.2 kg/ha imazosulfuron applied at the two- to four-leaf and 30.5-cm stages were similar to the nontreated check (all plots were maintained weed-free). For both application timings, yield decreased linearly as imazosulfuron rate increased. The application of imazosulfuron to watermelon at the 30.5-cm stage averaged across rates resulted in less injury at 15 DAT (16%) and greater yield (92,869 kg/ha) than watermelon treated at two- to four-leaf stage averaged across rates (29%, 83,560 kg/ha). Internal fruit quality was not affected by imazosulfuron.

Conventional grain sorghum is highly susceptible to POST grass control herbicides. Development of aryloxyphenoxypropionate-resistant grain sorghum could provide additional opportunities for POST herbicide grass control in grain sorghum. Field experiments were conducted at Hays and Manhattan, KS, to determine the effect of quizalofop rate and crop growth stage on injury and yield of aryloxyphenoxypropionate-resistant grain sorghum. Quizalofop was applied at 62, 124, 186, and 248 g ai ha−1 at sorghum heights of 8 to 10, 15 to 25, and 30 to 38 cm, which corresponded to early POST (EPOST), mid-POST (MPOST), and late POST (LPOST) application timings, respectively. Grain sorghum injury ranged from 0 to 68% at 1 wk after treatment (WAT); by 4 WAT, plants generally recovered from injury. The EPOST and MPOST applications caused 9 to 68% and 2 to 48% injury, respectively, whereas injury from LPOST was 0 to 16%, depending on rate. Crop injury from quizalofop was more prominent at rates higher than the proposed use rate in grain sorghum of 62 g ha−1. Grain yields were similar in treated and nontreated plots; applications of quizalofop at different timings did not reduce yield except when applied MPOST at the Manhattan site.

Experiments were conducted to determine the efficacy, absorption, and translocation of glyphosate, glufosinate, and imazethapyr with selected weed species. In the greenhouse glyphosate, glufosinate, and imazethapyr were applied at 0.25, 0.5, and 1 times their label rates of 1,121, 410, and 70 g ha−1, respectively, on 10- to 15-cm black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, ivyleaf morningglory, prairie cupgrass, velvetleaf, and yellow nutsedge. Glyphosate applied at the 1-time rate caused injury greater than or similar to injury from the 1-time rate of glufosinate or imazethapyr on black nightshade, common waterhemp, eastern black nightshade, field bindweed, giant ragweed, prairie cupgrass, and velvetleaf. The 1-time rate of glufosinate injured ivyleaf morningglory and yellow nutsedge more than did the 1-time rate of glyphosate or imazethapyr. Under field conditions glyphosate caused the greatest injury to common waterhemp, prairie cupgrass, and velvetleaf across plant growth stages. Giant ragweed and ivyleaf morningglory injury was more dependent on growth stage, with the 15- and 30-cm growth stages more susceptible to glyphosate than to glufosinate or imazethapyr. Differential response of these weed species may be caused by differences in herbicide translocation. Glyphosate was translocated more in both giant ragweed and ivyleaf morningglory, and these species were injured more by glyphosate than by glufosinate or imazethapyr at the larger growth stages.

Experiments were conducted during 2000 and 2001 at a total of 13 locations throughout Alabama, Georgia, Florida, North Carolina, and Texas to evaluate efficacy of herbicides at or below the manufacturer's suggested use rate. Herbicide applications included diclosulam and flumioxazin applied PRE alone or followed by imazapic applied early postemergence (EPOST). All possible combinations of diclosulam at 0, 13.5, or 27 g ai/ha and flumioxazin at 0, 53, or 105 g ai/ha applied PRE were included. Imazapic was applied at 35 g ai/ha. Ivyleaf morningglory was controlled more than 87% when imazapic was applied EPOST regardless of PRE herbicide. Pitted morningglory control > 67% was observed with applications of diclosulam (27 g/ha) followed by imazapic, diclosulam (13.5 g/ha) plus flumioxazin (53 g/ha), diclosulam (13.5 g/ha) plus flumioxazin (105 g/ha), and diclosulam (27 g/ha) plus flumioxazin (105 g/ha). Sicklepod was controlled more than 74% with flumioxazin (53 g/ha) followed by imazapic and diclosulam (27 g/ha) plus flumioxazin (105 g/ha) followed by imazapic. Florida beggarweed was controlled more than 84% by all PRE herbicide combinations except flumioxazin (53 g/ha) alone or diclosulam (27 g/ha) alone or with imazapic. Yellow nutsedge was controlled at least 90% with diclosulam at either rate followed by imazapic and by diclosulam plus flumioxazin followed by imazapic regardless of rate. Pod yield was generally higher when herbicides were applied regardless of herbicide combination or rate. Peanut yield was maximized with the lowest rates of flumioxazin or diclosulam PRE followed by imazapic EPOST.

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

Field studies were conducted in 2011 and 2012 at the Horticultural Crops Research Station near Clinton, NC, to determine ‘Covington' sweetpotato tolerance to S-metolachlor rate and application timing. Treatments were a factorial arrangement of four S-metolachlor rates (0, 1.1, 2.2, or 3.4 kg ai ha−1) and six application timings (0, 2, 5, 7, 9, or 14 d after transplanting [DAP]). Immediately following application, 1.9 cm of irrigation was applied to individual plots. Sweetpotato injury was minimal for all treatments (≤ 10%). No. 1 grade sweetpotato yield displayed a negative linear response to S-metolachlor rate, and decreased from 25,110 to 20,100 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Conversely, no. 1 sweetpotato yield displayed a positive linear response to S-metolachlor application timing and increased from 19,670 to 27,090 kg ha−1 as timing progressed from 0 to 14 DAP. Total marketable sweetpotato yield displayed a quadratic response to both S-metolachlor application rate and timing. Total marketable yield decreased from 44,950 to 30,690 kg ha−1 as S-metolachlor rate increased from 0 to 3.4 kg ha−1. Total marketable yield increased from 37,800 to 45,780 kg ha−1 as application timing was delayed from 0 to 14 DAP. At 1.1 kg ha−1S-metolachlor, sweetpotato storage root length to width ratio displayed a quadratic relationship to application timing and increased from 1.87 to 2.23 for applications made 0 to 14 DAP. At 2.2 kg ha−1 of S-metolachlor, sweetpotato length to width ratio displayed a quadratic response to application timing, increased from 1.57 to 2.09 for 0 to 10 DAP, and decreased slightly from 2.09 to 2.03 for 10 to 14 DAP. Application timing did not influence length to width ratio of sweetpotato storage roots for those plots treated with S-metolachlor at either 0 or 3.4 kg ha−1.

Field studies were conducted in 2013 at Houlka, MS and in 2014 at Houston, MS to evaluate herbicide programs for yellow nutsedge control and sweetpotato crop response. Treatments consisted of halosulfuron-methyl at 13, 26, and 34 g ai ha−1 2 wk after transplanting (WAP) followed by (fb) S-metolachlor at 856 g ai ha−1 4 WAP; a sequential application of 13 g ha−1 halosulfuron-methyl at 2 and 4 WAP; and halosulfuron-methyl at 13 g ha−1 plus either S-metolachlor or 1,123 g ai ha−1 alachlor 2 WAP. Crop injury in treated plots ranged from 29 to 44% at 3 WAP. Injury from the sequential application increased slightly between 3 and 5 WAP (29 to 38%), but decreased between 5 WAP and harvest (19%). Injury with all other treatments was unchanged from 5 WAP through harvest. The sequential application of halosulfuron-methyl provided the greatest control of yellow nutsedge throughout the duration of the study with ≥ 83% control from 5 WAP through harvest. Control from all other treatments ranged from 38 to 78% from 5 WAP through harvest. No. 1, canner, and marketable sweetpotato yields of the hand-weeded check were 19,900; 7,140; and 27,590 kg ha−1, respectively. No. 1, canner, and marketable yields of the weedy check were only 15, 51, and 25% of the hand-weeded check, respectively. With the exception of halosulfuron-methyl at 13 g ha−1 fb S-metolachlor, which was similar to the weedy check, no. 1 and marketable yields with all treatments were greater than the weedy check, but less than the weed-free check. A sequential application of halosulfuron-methyl and a tank mix of halosulfuron-methyl plus S-metolachlor would fit well into an overall yellow nutsedge management program in sweetpotato. However, as halosulfuron-methyl is not registered for use in sweetpotato, growers must continue to manage yellow nutsedge primarily with crop rotation and sanitation.

Field experiments from 1997 to 1999 examined cotton cv. ‘Coker 312’ that was genetically transformed to tolerate glufosinate. None of the glufosinate treatments caused visible injury to the glufosinate-tolerant cotton, but treatments were lethal to nontransformed or nonexpressing cotton. No glufosinate treatment adversely affected plant height at maturity, total number of nodes, bolls per plant, or boll positions. Glufosinate applications of 0.6 kg ha−1 made at eight stages of growth, ranging from cotyledon stage to 50% open boll, did not adversely affect yield or fiber quality as measured by micronaire or fiber length and strength. Sequential glufosinate applications up to four stages of growth from the zero- to one-leaf stage to the 14- to 15-leaf stage or individual glufosinate applications at 3.3 kg ha−1 made at the two- to three-leaf stage of growth also did not adversely affect yield or fiber quality. Overall yields in these studies were low relative to normal Texas Southern High Plains cotton yield because these studies were conducted using a Coker 312 parental line, which is generally a poor performer in this region. This research indicated that the transformation events for glufosinate tolerance in cotton were successful and the glufosinate-tolerance gene was expressed throughout the growing season. Transformation and field testing of other cotton varieties are needed to improve varietal performance on the Texas Southern High Plains.