Herbicide carrier water hardness and pH can be variable depending on the source and geographic location. Herbicide efficacy can be affected by the pH and hardness of water used for spray solution. Field and greenhouse studies were conducted to evaluate the effect of carrier water pH and hardness on premixed dicamba and glyphosate efficacy. Treatments were combinations of water pH at 4, 6.5, or 9; and water hardness at 0 (deionized water), 400, or 800 mg L−1 of CaCO3 equivalent. In the field study, dicamba and glyphosate were applied at 0.55 and 1.11 kg ae ha−1, respectively, and half of these rates were applied in the greenhouse study. There was no interaction between carrier water pH and hardness on dicamba and glyphosate efficacy; however, the main effects of carrier water pH and hardness were significant. Herbicide efficacy was reduced with carrier water at pH 9 compared with pH 4. In the field study, common lambsquarters, common ragweed, horseweed, or Palmer amaranth control was improved 6% or more at carrier water at pH 4 compared with pH 9. Similar results were observed with water pH for giant ragweed, Palmer amaranth, or pitted morningglory control in the greenhouse study. Carrier water hardness at 400 or 800 mg L−1 reduced common ragweed, giant ragweed, or horseweed control compared with 0 mg L−1. Similarly, common lambsquarters, Palmer amaranth, or pitted morningglory control was reduced at least 10% with carrier water hardness at 800 mg L−1 compared with 0 mg L−1. These results indicate carrier water at acidic pH and of no hardness is critical for dicamba and glyphosate application, and spray solution needs to be amended appropriately for an optimum efficacy.

Greenhouse studies were conducted to investigate the absorption, translocation, and metabolism of foliar-applied [14C]halosulfuron-methyl in cucumber, summer squash, pitted morningglory, and velvetleaf. Cucumber and summer squash were treated at the 4-leaf stage, whereas velvetleaf and pitted morningglory were treated at 10 cm. All plants were collected at 4, 24, 48, and 72 h after treatment (HAT) for absorption and translocation studies and an additional 96-HAT interval was included in the metabolism study. Absorption did not exceed 45% in summer squash, whereas it plateaued around 60% in velvetleaf and cucumber and reached 80% in pitted morningglory 72 HAT. None of the four species translocated more than 23% of absorbed halosulfuron out of the treated leaf. Translocation in cucumber and summer squash was predominantly basipetal, while acropetal movement prevailed in velvetleaf. No significant direction of movement was observed for pitted morningglory. Negligible translocation occurred toward the roots, regardless of plant species. Of the total amount of [14C]halosulfuron-methyl absorbed into the plants at 96 HAT, more than 80% remained in the form of the parent compound in velvetleaf, summer squash, and pitted morningglory, whereas less than 20% was detected in cucumber. Rapid and high herbicide metabolism may explain cucumber tolerance to halosulfuron-methyl, while lack of metabolism contributes to summer squash and velvetleaf susceptibility. Pitted morningglory tolerance may be due to limited translocation associated with some level of metabolism, but further research would be needed to investigate other potential causes.

Thiazopyr at 0.14, 0.28, and 0.42 kg ai/ha and pendimethalin at 1.1 kg ai/ha applied preemergence (PRE) were compared as components in weed management systems for no-till cotton. Mid- and late-season control of mixtures of large crabgrass, goosegrass, and fall panicum by thiazopyr at 0.28 kg/ha was 89 to 97% and 11 to 50%, respectively, compared with 11 to 38% midseason and 0 to 5% late-season control by pendimethalin. Thiazopyr at 0.42 kg/ha and pendimethalin controlled broadleaf signalgrass 44 and 0%, respectively, late in the season. Adding fluometuron PRE at 1.7 kg ai/ha had little to no effect on large crabgrass, goosegrass, and fall panicum control but increased broadleaf signalgrass control 47 to 79 percentage points compared with thiazopyr or pendimethalin alone. Late-season control of annual grasses by thiazopyr or pendimethalin plus fluometuron PRE followed by methazole plus MSMA early postemergence (POST)-directed and cyanazine plus MSMA late POST-directed was at least 95% at two locations and 80% at the third location. Common lambsquarters was controlled 54 and 95% in systems without and with fluometuron PRE, respectively. Acceptable control of ivyleaf, pitted, and tall morningglories at all locations and smooth pigweed at two of three locations was achieved only in systems with POST-directed herbicides. Adding POST-directed herbicides to systems with thiazopyr or pendimethalin plus fluometuron PRE increased cotton yield at two of three locations. Treatments had no effect on fiber quality.

Palmleaf morningglory (IPOWR) and pitted morningglory (IPOLA) were compared in field and greenhouse tests under simulated rice field conditions to quantify flood tolerance characteristics of the two species. IPOWR survived a 13-cm flood in the field if the flood was applied 12 days after planting (DAP) or later. In contrast, IPOLA did not survive floods applied before 19 DAP. Only IPOWR survived a 5-cm flood applied 5 DAP in the field. In the greenhouse, both species were unable to emerge from under 1 cm of soil when flooded greater than 1 cm deep. Although both species emerged from water-saturated soil, IPOWR emerged earlier and produced more dry weight than did IPOLA. Emergence from the water surface of 2-cm-tall IPOWR was better than that of IPOLA when submerged in water up to 7 cm deep, and total dry weight (as a percent of a nonflooded control) was two to four times greater for IPOWR. Even a 5-cm flood reduced leaf area, height, dry weight, and photosynthesis of IPOLA more than that of IPOWR. At 20 C and low oxygen (1%), germination percentage of IPOWR was about four times higher than IPOLA. Germination, growth, and certain physiological processes of IPOWR are more tolerant than those of IPOLA to moderately deep floods (and low soil oxygen levels). Thus, IPOWR is potentially a greater weed problem than IPOLA in rice fields. The fact that neither species was capable of emerging from soil under even shallow flood depths helps explain why morningglories are prevalent only in shallow or water-saturated areas on rice field levees.

Cotton and pitted morningglory emergence and dry weight decreased approximately 60 to 80% when these plants were grown under greenhouse conditions in the presence of increasing amounts (0.8 to 6.7 mg debris/g soil) of field-grown crimson clover or hairy vetch debris incorporated into the soil medium. Conversely, corn dry weight increased 20 to 75% when legume debris was placed on the soil surface; incorporated debris had very little effect on corn emergence or dry weight. Germination and seedling growth of corn, Italian ryegrass, cotton, pitted morningglory, and wild mustard decreased progressively, with species-dependent variation, when exposed to increasing concentrations (8.3 to 33.3 g debris/L) of aqueous crimson clover and hairy vetch extract. Mustard and ryegrass germination and growth were almost completely inhibited by full-strength extracts of both legumes. Bioassay species exhibited greater phytotoxic responses to hairy vetch than to crimson clover in the debris and extract studies. Emergence and growth of corn and cotton were not affected when planted into soil samples, containing root biomass and possible leaf and root exudates, collected from beneath field-grown hairy vetch and crimson clover plants. However, morningglory dry weight increased 35% in the presence of either legume root debris and accompanying soil.

Field experiments were conducted on eight weed species to determine if chlorimuron, fomesafen, imazethapyr, or sulfentrazone at two rates (labeled and one-half the labeled rate) were complementary tank mixtures with glyphosate at 210 and 420 g ai ha−1. Laboratory experiments were conducted on barnyardgrass, pitted morningglory, Palmer amaranth, and velvetleaf using radiolabeled glyphosate, chlorimuron, and imazethapyr to determine the absorption and translocation pattern of these herbicides applied alone and in combination. In the field, glyphosate plus chlorimuron tank mixtures were generally additive. Adding chlorimuron did not decrease absorption or translocation of 14C-glyphosate by barnyardgrass, pitted morningglory, or velvetleaf. Adding glyphosate increased absorption of 14C-chlorimuron by Palmer amaranth and velvetleaf. All four fomesafen plus glyphosate rate combinations were antagonistic to goosegrass, sicklepod, Palmer amaranth, and velvetleaf, and three of the four were antagonistic to barnyardgrass and entireleaf morningglory. Fomesafen decreased absorption and translocation of 14C-glyphosate in barnyardgrass, pitted morningglory, and velvetleaf. Ninety percent of glyphosate plus imazethapyr combinations were additive or synergistic, with all rate combinations synergistic for pitted morningglory. Adding glyphosate to imazethapyr increased absorption of 14C-imazethapyr by Palmer amaranth and velvetleaf. Glyphosate plus sulfentrazone tank mixtures were antagonistic at all rate combinations for barnyardgrass and Palmer amaranth and at three of the four combinations for goosegrass and entireleaf morningglory, indicating that these herbicides are not complementary in tank mixtures.

Field studies were conducted in 2002 and 2003 to determine whether canopy formation influences pitted morningglory, common cocklebur, and sicklepod emergence in surface-tilled soybean. Each weed species was broadcast seeded before planting soybean in 19- and 97-cm-wide rows. Weed emergence beneath soybean was monitored after soybean emergence and compared with weed emergence in the absence of soybean (bareground treatment). Magnitude of daily diurnal soil temperature fluctuations diminished after soybean canopy formation, and light interception by soybean was positively related to the reduction in soil temperature. Canopy formation (50% light interception) occurred 16 to 17 d later in wide compared with narrow rows in both years. The red/far-red ratio of light available to seed on or near the soil surface was reduced from as much as 1.2 in full sunlight to less than 0.1 in the presence of a dense soybean canopy. Pitted morningglory emergence was not influenced by soybean canopy formation, whereas common cocklebur and sicklepod emergence were reduced as much as 33 and 68%, respectively. Although common cocklebur and sicklepod emergence diminished after soybean canopy formation, a small portion of the seedbank of both species emerged beneath the canopy. This research indicates that in a tilled system, emergence of some weed species is diminished by presence of an overlying canopy, but emergence does not completely cease with canopy formation. Late-season emergence of sicklepod and common cocklebur beneath a soybean canopy may contribute to replenishment of the soil seedbank, especially if these late-emerging cohorts are capable of surviving until the light environment is favorable for seed production.

Field experiments were conducted in Georgia to evaluate weed control and crop tolerance with glufosinate applied to ‘PHY 485 WRF®’ cotton. This glyphosate-resistant cotton also contains a gene, used as a selectable marker, for glufosinate resistance. Three experiments were maintained weed-free and focused on crop tolerance; a fourth experiment focused on control of pitted morningglory and glyphosate-resistant Palmer amaranth. In two experiments, PHY 485 WRF cotton was visibly injured 15 and 20% or less by glufosinate ammonium salt at 430 and 860 g ae/ha, respectively, applied POST two or three times. In a third experiment, glufosinate at 550 g/ha injured cotton up to 36%. Pyrithiobac or glyphosate mixed with glufosinate did not increase injury compared to glufosinate applied alone; S-metolachlor mixed with glufosinate increased injury by six to seven percentage points. Cotton injury was not detectable 14 to 21 d after glufosinate application, and cotton yields were not reduced by glufosinate or glufosinate mixtures. A program of pendimethalin PRE, glyphosate applied POST twice, and diuron plus MSMA POST-directed controlled glyphosate-resistant Palmer amaranth only 17% late in the season. S-metolachlor included with the initial glyphosate application did not increase control, and pyrithiobac increased late-season control by only 13 percentage points. Palmer amaranth was controlled 90% or more when glufosinate replaced glyphosate in the aforementioned system. Pitted morningglory was controlled 99% by all glufosinate programs and mixtures of glyphosate plus pyrithiobac. Seed cotton yields with glufosinate-based systems were at least 3.3 times greater than yields with glyphosate-based systems because of differences in control of glyphosate-resistant Palmer amaranth.

Water is the primary carrier for herbicide application, and carrier-water–related factors can influence herbicide performance. In a greenhouse study, premixed formulation of glyphosate plus dicamba was mixed in deionized (DI) water at 5, 18, 31, 44, or 57 C and applied immediately. In a companion study, glyphosate and dicamba formulation was mixed in DI water at temperatures of 5, 22, 39, or 56 C and sprayed after the herbicide solution was left at the respective temperatures for 0, 6, or 24 h. In both studies, glyphosate plus dicamba was applied at 0.275 plus 0.137 kg ae ha−1 (low rate), and 0.55 plus 0.275 kg ha−1 (high rate), respectively, to giant ragweed, horseweed, Palmer amaranth, and pitted morningglory. Glyphosate plus dicamba applied at a low rate with solution temperature of 31 C provided 14% and 26% greater control of giant ragweed and pitted morningglory, respectively, compared to application at solution temperature of 5 C. At both rates of glyphosate and dicamba formulation, giant ragweed and pitted morningglory control was 15% or greater at solution temperature of 44 C compared to 5 C. Weed control was not affected with premixture of glyphosate and dicamba applied ≤ 24 h after mixing herbicide. When considering solution temperature, glyphosate and dicamba applied at low rate provided 13 and 6% greater control of Palmer amaranth and pitted morningglory, respectively, with solution temperature of 22 C compared to 5 C. Similarly, giant ragweed control was 8% greater with solution temperature of 39 C compared to 5 C. Glyphosate and dicamba applied at high rate provided 8% greater control of giant ragweed at solution temperature of 22 or 39 C compared to 5 C. Therefore, activity of premixed glyphosate and dicamba could be reduced with spray solution at lower temperature; however, the result is dependent on weed species.

Field studies were conducted in five states at six locations from 2002 through 2003 to evaluate weed control and cotton response to early POST (EPOST), POST/POST-directed spray (PDS), and late POST-directed (LAYBY) systems using glyphosate-trimethylsulfonium salt (TM), s-metolachlor, trifloxysulfuron, prometryn, and MSMA. Early POST applications were made from mid May through mid June; POST/PDS applications were made from early June through mid July; and LAYBY applications were made from early July through mid August. Early season cotton injury and discoloration was minimal (< 1%) with all treatments; mid- and late-season injury was minimal (< 2%) except for trifloxysulfuron POST (11 and 9%, respectively). Annual grasses evaluated included barnyardgrass, broadleaf signalgrass, goosegrass, and large crabgrass. Broadleaf weeds evaluated included entireleaf morningglory, pitted morningglory, sicklepod, and smooth pigweed. For the EPOST, POST/PDS, and LAYBY applications, weeds were at cotyledon to 10 leaf, 1 to 25 leaf, and 2 to 25 leaf stage, respectively. Annual broadleaf and grass control was increased with the addition of s-metolachlor to glyphosate-TM EPOST systems (85 to 98% control) compared with glyphosate-TM EPOST alone (65 to 91% control), except for sicklepod control where equivalent control was observed. Annual grass control was greater with glyphosate-TM plus trifloxysulfuron PDS than with trifloxysulfuron POST or PDS, or trifloxysulfuron plus MSMA PDS (90 to 94% vs. 75 to 83% control). With few exceptions, broadleaf weed control was equivalent for trifloxysulfuron applied POST alone or PDS alone or in combination with glyphosate-TM PDS or MSMA PDS herbicide treatments (81 to 99% control). The addition of a LAYBY herbicide treatment increased broadleaf weed control by 11 to 36 percentage points compared with systems without a LAYBY. Cotton lint yield increased 420 kg/ha with the addition of s-metolachlor to glyphosate-TM EPOST treatments compared with systems without s-metolachlor EPOST. Cotton lint yield was increased 330 to 910 kg/ha with the addition of a POST herbicide treatment compared with systems without a POST/PDS treatment. The addition of a LAYBY herbicide treatment increased cotton lint yield by 440 kg/ha compared with systems without a LAYBY.

Experiments were conducted at the Upper Coastal Plain Research Station near Rocky Mount and at the Peanut Belt Research Station near Lewiston-Woodville in 2002 and 2003. Peanut injury was minimal (< 5%) with all soil-applied programs. S-Metolachlor PRE alone or in mixture with sulfentrazone, diclosulam, or flumioxazin controlled annual grasses similarly (66 to 87%). The addition of imazapic plus 2,4-DB POST increased annual grass control (> 93%). Sulfentrazone or diclosulam in mixture with S-metolachlor were the best PRE options, with 94% and 92% control of yellow and purple nutsedge, respectively, with flumioxazin being least effective at 70%. Diclosulam and flumioxazin in mixture with S-metolachlor were the best PRE options, with 99% and 93%, respectively for common ragweed control, whereas sulfentrazone was the least effective at 65%. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin PRE were similar (87 to 90%) for common lambsquarters control. S-Metolachlor in mixture with sulfentrazone, diclosulam, or flumioxazin provided similar levels of entireleaf, ivyleaf, pitted, and tall morningglory control (87, 86, and 87%, respectively) and better than S-metolachlor alone at 64%. Flumioxazin in mixture with S-metolachlor was the best PRE option for control of Palmer amaranth at 96%, whereas diclosulam with S-metolachlor was the best PRE option for control of eclipta at 100%. The prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST and imazapic plus 2,4-DB POST were similar for all morningglory species (> 96%) and Palmer amaranth control (93 and 97%, respectively). Peanut treated with S-metolachlor plus diclosulam PRE numerically yielded the highest at 3,210 kg/ha, but were statistically equivalent to S-metolachlor plus flumioxazin PRE at 3,040 kg/ha. Peanut treated with imazapic plus 2,4-DB POST yielded the most at 3,400 kg/ha, while peanut treated with a prepackaged mixture of acifluorfen and bentazon plus 2,4-DB POST yielded less (3,070 kg/ha).

Laboratory and greenhouse experiments were conducted to determine the effect of light, temperature, solution pH, solution osmotic potential, and oxygen concentration on pitted morningglory germination and radicle plus hypocotyl elongation, and seeding depth on its subsequent emergence. Daily exposure of seed to natural light resulted in lower germination than in darkness, whereas germination was not influenced by brief exposure to red or far-red light. Germination occurred over a wide range of constant temperatures, from 7.5 to 52.5 C, with optimum germination between 20 and 25 C. Germination occurred at solution pH range of 3 to 10 and was optimal from pH 6 to 8. Radicle plus hypocotyl elongation was influenced by the interaction of temperature and solution pH. A combination of acidic medium (pH 6) and high temperature (30 C) resulted in the greatest radicle plus hypocotyl length of 7.6 cm after a 7-d incubation. Germination and radicle plus hypocotyl elongation, averaged over the 15 and 30 C temperature, decreased with increasing moisture stress, with less than 3% normalized germination at −1.0 MPa. Germination was 29, 40, and 51% at 2, 10, and 20% oxygen, respectively, averaged over 15 and 30 C. Germination of seed lying on the soil surface covered with filter paper or without any cover was similar, averaging 64%. Normalized emergence, relative to germination on the soil surface, decreased with increasing burial depth to 4% emergence at 10 cm, with a mean emergence depth of 4.1 cm, averaged across two soil types.

Greenhouse studies were conducted to evaluate absorption, translocation, and metabolism of 14C-glufosinate in glufosinate-resistant cotton, nontransgenic cotton, Palmer amaranth, and pitted morningglory. Cotton plants were treated at the four-leaf stage, whereas Palmer amaranth and pitted morningglory were treated at 7.5 and 10 cm, respectively. All plants were harvested at 1, 6, 24, 48, and 72 h after treatment (HAT). Absorption of 14C-glufosinate was greater than 85% 24 h after treatment in Palmer amaranth. Absorption was less than 30% at all harvest intervals for glufosinate-resistant cotton, nontransgenic cotton, and pitted morningglory. At 24 HAT, 49 and 12% of radioactivity was translocated to regions above and below the treated leaf, respectively, in Palmer amaranth. Metabolites of 14C-glufosinate were detected in all crop and weed species. Metabolism of 14C-glufosinate was 16% or lower in nontransgenic cotton and pitted morningglory; however, metabolism rates were greater than 70% in glufosinate-resistant cotton 72 HAT. Intermediate metabolism was observed for Palmer amaranth, with metabolites comprising 20 to 30% of detectable radioactivity between 6 and 72 HAT.

Field experiments were conducted from 1997 through 1999 to evaluate interspecific interference between pitted morningglory at 0, 10, 16, and 62 plants m−2 and drill-seeded, glyphosate-resistant soybean as influenced by soybean population and a single glyphosate application of 1.12 kg ai ha−1. Photosynthetic rate of soybean was not influenced by pitted morningglory density or glyphosate use 2 wk after treatment (WAT). Photosynthetic rate of soybean 12 WAT was reduced by 21 and 91% with 62 treated and untreated pitted morningglory plants m−2, respectively, whereas 10 treated and untreated pitted morningglory plants m−2 had no effect on the soybean photosynthetic rate. Pitted morningglory photosynthetic rate 2 and 12 WAT was reduced by 64 and 80%, respectively, when treated with glyphosate. The reduction in the photosynthetic rate of glyphosate-treated pitted morningglory was partially attributed to shading by soybean, whereas untreated plants were fully exposed to sunlight. Glyphosate-treated pitted morningglory at 10 and 16 plants m−2 did not reduce the rate of soybean leaf area index (LAI) accumulation; however, when the density was increased to 62 pitted morningglory plants m−2, soybean LAI decreased from 1.19 to 0.88 for each accumulated 100 growing degree days. Pitted morningglory produced a maximum of 24 million seeds ha−1 in the absence of glyphosate with 217,000 soybean plants ha−1. Pitted morningglory seed production declined with increasing soybean seeding rate in the absence of glyphosate, with a 41% reduction occurring when soybean population increased from 217,000 to 521,000 plants ha−1. Seed production of treated pitted morningglory ranged from 380,000 to 700,000 seeds ha−1. Soybean seed yield was not influenced by pitted morningglory density when treated with glyphosate. Untreated pitted morningglory at 10, 16, and 62 plants m−2 reduced soybean seed yield by 47, 62, and 81%, respectively. Competitiveness of untreated soybean increased with soybean seeding rate, resulting in 22% less yield loss with 521,000 than with 217,000 plants ha−1. Soybean seed yield was not reduced by 10 and 16 glyphosate-treated pitted morningglory plants m−2, but a 9% loss in yield occurred with 62 pitted morningglory plants m−2. Averaged over all pitted morningglory densities, glyphosate-treated pitted morningglory failed to reduce soybean seed yield at each of the three soybean densities. Following a single application of glyphosate, no apparent benefit was noted from increasing the soybean population above 217,000 plants ha−1.

Field studies were conducted in Fayetteville, AR, to determine the response of 38 pitted morningglory accessions to fomesafen, chlorimuron, and glyphosate when applied postemergence over-the-top (POT) at 9 g ai/ha, 420 g ai/ha, and 840 g ae/ha, respectively, to four-leaf, 15-cm-tall pitted morningglory. Visual control following chlorimuron application ranged from 82 to 95% 3 wk after treatment (WAT). Visual control of accessions with fomesafen ranged 34 to 84% 3 WAT. Variability in visual control following fomesafen application was documented among accessions collected from similar geographic locations in west-central and southwest Arkansas, central and southeast Louisiana, and west-central Mississippi. Glyphosate controlled pitted morningglory accessions 81 to 89% 3 WAT. Data indicate that weed management programs should be field specific where fomesafen use is intended.

Research was conducted in North Carolina to compare weed control by various rates of imazapic POST alone or following diclosulam PRE. In a second experiment, weed control by imazapic applied POST alone or with acifluoren, diclosulam, or 2,4-DB was compared. In a final experiment, yellow nutsedge control by imazapic alone and with the fungicides azoxystrobin, chlorothalonil, pyraclostrobin, and tebuconazole was compared. Large crabgrass was controlled more effectively by imazapic POST than diclosulam PRE. Common lambsquarters, common ragweed, and eclipta were controlled more effectively by diclosulam PRE than imazapic POST. Nodding spurge was controlled similarly by both herbicides. Few differences in control were noted when comparing imazapic rates after diclosulam PRE. Applying either diclosulam PRE or imazapic POST alone or in combination increased peanut yield over nontreated peanut in five of six experiments. Few differences in pod yield were noted when comparing imazapic rates. Acifluorfen, diclosulam, and 2,4-DB did not affect entireleaf morningglory, large crabgrass, nodding spurge, pitted morningglory, and yellow nutsedge control by imazapic. Eclipta control by coapplication of imazapic and diclosulam exceeded control by imazapic alone. The fungicides azoxystrobin, chlorothalonil, pyraclostrobin, and tebuconazole did not affect yellow nutsedge control by imazapic.

An experiment was conducted at two locations in Georgia and one location in North Carolina during 1994 and 1995 to evaluate weed management systems utilizing pyrithiobac applied preemergence (PRE) in conventional-tillage bromoxynil-resistant cotton. Weed management systems evaluated included different combinations of pyrithiobac PRE, bromoxynil or bromoxynil plus MSMA applied early postemergence (EPOST), bromoxynil applied postemergence (POST), and cyanazine plus MSMA applied late postemergence-directed (LAYBY). Pyrithiobac PRE improved control of Florida beggarweed, pitted morningglory, prickly sida, sicklepod, and spurred anoda compared with systems that did not include pyrithiobac PRE. Averaged across locations, pyrithiobac PRE increased cotton lint yields 330 kg ha−1. Bromoxynil applied EPOST or POST increased weed control and cotton lint yield. Bromoxynil EPOST, POST, or EPOST plus POST did not control sicklepod. The addition of MSMA to bromoxynil EPOST improved sicklepod control. Two applications of bromoxynil controlled more pitted morningglory and sicklepod than one application. Control of all dicotyledonous weeds was increased by cyanazine plus MSMA LAYBY, and this treatment increased yields at all locations. Cotton was not injured by pyrithiobac PRE or by bromoxynil applied EPOST or POST, but temporary visual injury was observed with EPOST treatments of MSMA.

Field trials were conducted in the spring of 2004 and the spring and summer of 2005 to evaluate cantaloupe tolerance to rimsulfuron and halosulfuron applied to cantaloupe at the two-leaf stage, five- to six-leaf stage, plants having 30- to 40-cm vines, and plants having up to 5-cm-diam melons. Additionally, control of eight weed species was evaluated in these trials in 2005. Cantaloupe plant injury from rimsulfuron differed among application timings and trials, but applications were generally more injurious when applied at the two early crop stages. Halosulfuron was less injurious to cantaloupe, but 31 and 14% injury occurred following the two-leaf and five- to six-leaf applications, respectively, in the second trial in 2005. In the first trial of 2005, number of marketable melons the first week of harvest was lower for all halosulfuron applications compared with the nontreated control (30 to 37% reduction). In the second trial of 2005, total number of marketable melons was comparable to the nontreated control for each of the halosulfuron treatments, except the five- to six-leaf and up to 5-cm-diam melon applications. Injury estimates were poor indicators of occurrence or absence of delays in crop earliness or number of marketable melons. Rimsulfuron was generally effective (≥ 80% control) in controlling seedling Texas panicum, large crabgrass, tall morningglory, pitted morningglory, and Palmer amaranth, but was ineffective against yellow and purple nutsedge and goosegrass. Halosulfuron was effective in controlling yellow and purple nutsedge, but was ineffective against Texas panicum, large crabgrass, goosegrass, pitted morningglory, tall morningglory, and Palmer amaranth.

An experiment conducted at five locations in North Carolina during 1998 and 1999 evaluated weed management systems in cotton with CGA-362622 and pyrithiobac. Weed management systems evaluated different combinations with or without fluometuron preemergence (PRE) followed by (fb) CGA-362622 early postemergence (EPOST), postemergence (POST), or EPOST + POST; or pyrithiobac EPOST fb prometryn plus MSMA late postemergence directed (LAYBY) or no LAYBY treatment. The weed species evaluated include common ragweed, entireleaf morningglory, pitted morningglory, prickly sida, sicklepod, tall morningglory, and yellow nutsedge. Fluometuron PRE improved the control of all weed species by at least 17 percentage points and increased cotton lint yield compared with the systems that did not use fluometuron PRE. Prometryn plus MSMA LAYBY improved the control of all weed species and increased lint yield compared with the systems that did not use prometryn plus MSMA LAYBY when PRE or POST herbicides were used. Control with CGA-362622 at all application timings was greater than 70% for all weed species evaluated (common ragweed, entireleaf morningglory, pitted morningglory, sicklepod, tall morningglory, and yellow nutsedge), except prickly sida. Control of all three morningglory species and prickly sida was at least 70% with pyrithiobac, whereas control of common ragweed, sicklepod, and yellow nutsedge was lower. The only cotton that yielded over 800 kg ha−1 was treated with fluometuron PRE fb CGA-362622 EPOST, POST, or EPOST + POST fb prometryn plus MSMA LAYBY. Cotton treated with pyrithiobac EPOST gave yields that were similar to those given by cotton treated with CGA-362622 EPOST in systems with fluometuron PRE and less than those given by cotton treated with CGA-362622 EPOST in systems without fluometuron PRE. Early-season injury with CGA-362622 was greater than 60% at Clayton and Rocky Mount in 1998, whereas 12% or less injury was observed at the other locations. Pyrithiobac resulted in 25 to 45% injury at these two locations. No injury was observed 45 d after treatment.

Field and greenhouse studies were conducted to investigate the compatibility of MSMA in a tank mixture with glyphosate or glufosinate for broadleaf and grass weed control. Glyphosate, glufosinate, and MSMA were evaluated at 0.5×, 1×, and 2× rates, with 1× rates of 0.84 kgae/ha, 0.5 kgai/ha, and 2.2 kgai/ha, respectively. Glyphosate and glufosinate provided similar levels of control for most weed species and were often more efficacious than MSMA alone. Glyphosate controlled Palmer amaranth better than glufosinate. Glufosinate controlled hemp sesbania, pitted morningglory, and ivyleaf morningglory better than glyphosate at one location. Weed control was not improved with the addition of MSMA to glyphosate or glufosinate when compared with either herbicide alone. MSMA antagonized glyphosate efficacy on barnyardgrass, browntop millet, hemp sesbania, Palmer amaranth, and redroot pigweed. MSMA antagonized glufosinate efficacy on browntop millet, hemp sesbania, ivyleaf morningglory, johnsongrass, Palmer amaranth, pitted morningglory, prickly sida, redroot pigweed, and velvetleaf. Antagonism of glyphosate or glufosinate by MSMA was often overcome by applying the 2× rate of either herbicide alone. MSMA is not a compatible tank-mixture partner with glyphosate or glufosinate for weed control in cotton.