POST control of cowpea in cotton was evaluated in 1990 and 1991. Early POST-directed (EPD) application of fluometuron + MSMA provided 89% cowpea control 2 wk after treatment. Cowpea control 4 wk after the early treatments was similar with fluometuron + MSMA EPD and sequential directed applications of MSMA followed by (fb) MSMA, methazole + MSMA fb cyanazine + MSMA, and fluometuron + MSMA fb cyanazine + MSMA. The average reduction in cowpea biomass 12 wk after planting with these treatments was 93%. MSMA fb MSMA POST-directed was the only treatment with a lint cotton yield similar to that of weed-free cotton. Lint cotton yields with fluometuron + MSMA, methazole + MSMA fb cyanazine + MSMA, and fluometuron + MSMA fb cyanazine + MSMA were similar to those obtained with MSMA fb MSMA.

Experiments were conducted to compare control of entireleaf morningglory with POST applications of DPX-PE350 applied with no adjuvant, a nonionic surfactant, or crop oil concentrate in spray volumes of 94, 235, and 375 L ha−1. Control was greater with a nonionic surfactant or crop oil concentrate than with no adjuvant and control with crop oil concentrate exceeded control with the nonionic surfactant. Spray volume had no effect on efficacy. DPX-PE350 was more effective when applied to foliage only or to soil plus foliage than when applied to soil only after emergence of entireleaf morningglory. Control from soil-only applications was lower on a silty clay soil than on a silt loam soil. Except for sicklepod, mixing DPX-PE350 with fluometuron or MSMA had little effect on weed control.

Two experiments were conducted over a two-year period for large crabgrass control in centipedegrass. The experiments were: (a) sequential applications of PRE and POST herbicides, and (b) POST herbicides applied as sequential or tank-mixed applications. Large crabgrass control was greater than 80% throughout the spring and summer when dithiopyr was applied PRE at 0.14 kg/ha late in February or when tank mixed at the same rate with sethoxydim at 0.11 kg/ha and applied POST in late May. Control was similar from a sequential program of dithiopyr applied PRE at 0.14 kg/ha in February and followed either by dithiopyr at 0.14 kg/ha or sethoxydim at 0.11 kg/ha as POST in early to mid-summer. Dithiopyr at 0.28 kg/ha as a POST application in late May did not control large crabgrass consistently. Control was > 80% for 6 to 8 wk when the POST dithiopyr treatment was repeated at the same rate 1 mo later. Sethoxydim applied POST controlled large crabgrass greater than 80% throughout the spring and summer when applied once at 0.22 kg/ha or twice at 0.11 kg/ha in each of two applications. Dithiopyr applied alone or with sethoxydim as sequential or tank-mixed treatments caused slight to moderate centipedegrass injury but was commercially acceptable (< 30%). However, injury from tank-mix herbicides was similar to either applied alone. Quinclorac severely injured (> 30%) centipedegrass, and 8 to 10 wk were required for recovery.

The tolerance of four established seeded common bermudagrass types to PRE and POST herbicides was evaluated. Pendimethalin at 3.4 kg ai/ha, oryzalin at 3.4 kg ai/ha, and dithiopyr at 0.8 kg ai/ha suppressed the quality of bermudagrass 8 to 16% more than oxadiazon at 4.5 kg ai/ha and prodiamine at 0.8 kg ai/ha. When interactions of PRE herbicide by bermudagrass cultivars occurred, oxadiazon, prodiamine, and pendimethalin suppressed the quality of ‘common’ and ‘Sahara’ 18 to 20% more than ‘Tropica’; oryzalin suppressed the quality of common and Sahara 11 to 18% more than Tropica; and dithiopyr suppressed the quality of common and Sahara 9% more than Tropic and ‘Cheyenne.’ The quality of Cheyenne treated with either oxadiazon, prodiamine, or pendimethalin was generally intermediate to the other cultivars. When POST herbicides by bermudagrass cultivar interactions occurred, MSMA plus metribuzin applied at 2.2 + 0.1 kg ai/ha injured common and Sahara an average of 10 to 12% higher than Tropica during 1993 and 1994. Diclofop applied at 1.1 kg ai/ha and dicamba applied at 0.6 kg ae/ha injured common 9 to 12% higher than Tropica. There was no difference in injury to cultivars when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg ae/ha. In general, Tropica was affected least by PRE and POST herbicide treatments, while common and Sahara cultivars were affected the most.

Sequential applications of MSMA plus metribuzin with selected plant growth regulators interacted synergistically and increased injury of ‘Tifway’ bermudagrass 1 and 2 wk after treatment. However, the higher injury at 3 wk after treatment, from sequential MSMA plus metribuzin with flurprimidol plus mefluidide or paclobutrazol with mefluidide, was additive. The vegetative growth suppression of bermudagrass at 2 wk after treatment with 2,4-D plus mecoprop plus dicamba with flurprimidol was antagonistic. The higher growth suppression 2 wk after treatment for MSMA plus metribuzin and flurprimidol plus mefluidide was additive compared to flurprimidol with mefluidide alone.

Preemergence (PRE) and postemergence (POST) herbicides were sequentially applied to common bermudagrass over a two-year period to determine the lowest herbicide rates required to maintain acceptable large crabgrass and goosegrass control. Large crabgrass control was consistently higher in late August when MSMA at 2.2 kg ha−1 was applied to plots previously treated with dithiopyr at 0.3 kg ha−1 (99%) in 1991, and either pendimethalin at 1.1 kg ha−1 (95%) or oxadiazon at 1.1 kg ha−1 (94%) in 1992 than when either herbicide was applied alone (≤ 79%). Goosegrass control was also higher in late August when MSMA plus metribuzin at 2.0 + 0.14 kg ha−1 was applied to plots treated with pendimethalin at 1.7 kg ha−1 (71%) in 1991, with oxadiazon at ≤ 2.2 kg ha−1 (≤ 89%) in 1992, and with dithiopyr at 0.4 kg ha−1 (≤ 96%) both years than when the herbicides were applied alone. Diclofop at 1.1 kg ha−1 applied alone as POST controlled ≥ 96% goosegrass throughout the two-year period.

Field experiments were conducted in 1994 and 1995 to determine if the sodium salt of pyrithiobac or bromoxynil applied in a low-volume, air-assist spray system controlled entireleaf morningglory, pitted morningglory, and smallflower morningglory as well as treatments applied with a conventional hydraulic fan spraying system, and to determine if herbicide rates could be reduced when using the low-volume spraying system. Pyrithiobac at 0.035 and 0.071 kg ai/ha and bromoxynil at 0.56 and 1.12 kg ai/ha were applied alone and in combination with DSMA at 1.7 kg ai/ha or MSMA at 1.7 kg ai/ha. Spraying systems were calibrated to deliver 26 L/ha and 140 L/ha for the low-volume and conventional systems, respectively. No significant differences in control were noted between low-volume and conventional spray systems when herbicides were applied at the suggested use rates of 0.071 and 1.12 kg ai/ha for pyrithiobac and bromoxynil, respectively. Morningglory control was reduced when pyrithiobac and bromoxynil were applied at one-half the suggested use rate regardless of the spraying systems. Bromoxynil alone generally controlled pitted and entireleaf morningglory better than pyrithiobac alone regardless of rate and application method. However, pyrithiobac generally provided better control of smallflower morningglory than bromoxynil. Adding MSMA or DSMA to bromoxynil and pyrithiobac increased control of both weed species.

Two or three applications of MSMA applied alone were ineffective in controlling smutgrass in common bermudagrass turf. Where atrazine at 2.2 kg ai/ha or simazine at 2.2 kg/ha was followed by two or three MSMA applications at 2.2 or 4.5 kg/ha, smutgrass control was increased. Metribuzin followed by two or three applications of MSMA was only slightly better than MSMA applied alone. Up to 35% injury to bermudagrass was observed 2 wk after the initial MSMA or the MSMA-triazine treatment, but complete recovery was evident 2 to 4 wk later, even with one or two follow-up MSMA applications at weekly intervals. Bermudagrass injury from the application of triazines followed with MSMA did not differ from MSMA applied alone in two of three experiments. In one experiment, atrazine or metribuzin followed with MSMA applications caused 10 to 25% more bermudagrass injury than MSMA applied alone.

A two-year experiment was conducted to determine if tank-mixes of postemergence (POST) herbicides would consistently control large crabgrass and goosegrass in common bermudagrass turf compared to herbicide alone treatments. Tank-mixes of MSMA plus quinclorac at 2.2 + 0.6 kg/ha effectively controlled large crabgrass (≥ 81%) for 10 to 11 weeks during 1993 and 1994. The control from MSMA plus dithiopyr at 2.2 + 0.3 kg/ha was higher during this period than when each herbicide was applied alone at the same rate. There was no increase in large crabgrass control from tank-mixes of MSMA and diclofop applied in a single application, when compared with two applications of MSMA applied at 2.2 kg/ha. Goosegrass control at 9 wk after tank-mixed treatments of MSMA (2.2 kg/ha) and diclofop (≥ 0.3 kg/ha) in 1994 was lower (12 to 28%) than when diclofop at 1.1 kg/ha was applied alone (85%). Tank-mixes of MSMA with quinclorac or dithiopyr did not control goosegrass. In general, common bermudagrass injury was no higher from herbicide combinations than when each was applied alone. An exception occurred at 1 wk after treatment in 1993 when common bermudagrass injury was higher from tank-mixes of MSMA plus diclofop at 2.2 + 1.1 kg/ha, than when either herbicide was applied alone.

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.

An experiment was conducted at four locations in North Carolina during 1994 and 1995 to evaluate weed control, cotton yield, fiber quality, and net returns in no-tillage bromoxynil-tolerant cotton. The experiment focused on using bromoxynil or pyrithiobac sodium applied early POST over-the-top as alternatives to fluometuron plus MSMA applied early POST directed. Fluometuron plus MSMA was more effective than bromoxynil or pyrithiobac sodium on tall morningglory, large crabgrass, goosegrass, and broadleaf signalgrass. Bromoxynil and fluometuron plus MSMA were similarly effective on common lambsquarters, common ragweed, and eclipta and more effective than pyrithiobac sodium. Pyrithiobac sodium and fluometuron plus MSMA were similarly effective on smooth pigweed and Palmer amaranth and more effective than bromoxynil. Prickly sida control by bromoxynil and pyrithiobac sodium was equal to or greater than control by fluometuron plus MSMA. All early POST herbicides controlled pitted morningglory similarly. Regardless of the early POST herbicides used, fluometuron applied PRE and cyanazine plus MSMA applied late POST directed increased control of most weeds and increased cotton yield and net returns. Bromoxynil and pyrithiobac sodium effectively substituted for fluometuron plus MSMA only in systems that included fluometuron applied PRE and cyanazine plus MSMA applied late POST directed. Effects of herbicide systems on cotton fiber quality were minor.

The uptake, translocation, and metabolism of 14C-MSMA in organic arsenical-resistant (R) and -susceptible (S) Mississippi biotypes of common cocklebur were investigated. The two biotypes did not differ significantly with respect to either uptake, total translocation, or translocation pattern of 14C-MSMA plus its radiolabeled metabolites regardless of whether plants were pre-treated with 1.12 kg ai ha−1 of unlabeled MSMA or treated only with radiolabeled material. Absorption of 14C-MSMA was greater in unlabeled MSMA-pretreated plants than untreated plants, whereas the percent of total absorbed 14C-MSMA that was translocated out of the 14C-MSMA-treated leaf was almost the same in MSMA-pretreated and untreated plants. Qualitative detection of 14C-MSMA distribution by autoradiographs confirmed quantitative results obtained with radioassays. Herbicide metabolism in the 14C-treated leaf showed that MSMA was not readily broken down in both biotypes and the extractable 14C was the same. Uptake, translocation, and metabolic degradation were not involved in the mechanism of resistance of the resistant-Mississippi biotype common cocklebur to MSMA.

Field experiments conducted over three years at Stoneville, MS evaluated invert emulsion and oil diluents on the efficiacy of glyphosate and MSMA on purple nutsedge. The herbicides were applied at 0.6 and 1.1 kg ai/ha in an invert emulsion (oil-in-water) and a paraffinic oil at 19 L/ha (low-volume) and in water with a non-ionic surfactant (0.25% v/v) at 187 L/ha (high-volume). Purple nutsedge control with both herbicides was greater with the low-volume, invert emulsion and oil diluent applications than with high-volume, water diluent applications. Glyphosate and MSMA at 1.1 kg/ha in the oil diluent controlled purple nutsedge at least 88% when compared with the invert emulsion (≥ 75 and ≥ 76%, respectively) and water (≥ 42 and ≥ 44%, respectively) diluents. Cotton injury and seed cotton yields were unaffected by any treatment with MSMA but glyphosate with each diluent caused unacceptable cotton injury and seed cotton yield reduction.

Research was conducted to determine an effective morningglory control system for cotton grown in central Texas, Prometryn applied PRE or directed-POST applications of methazole or methazole + MSMA did not always adequately control ivyleaf, entireleaf, and seedling sharppod morningglories. However, adequate control of the above species plus pitted morningglory was achieved with a management system that used a dinitroaniline applied PPI or PRE, prometryn applied PRE (0.9 kg ai ha−1), followed by methazole (0.56 kg ha−1) or methazole + MSMA (0.56 + 1.80 kg ha−1) directed POST to cotton 10 to 15 cm high.

Asulam applied POST alone and in mixtures with residual herbicides and with DSMA and MSMA was evaluated for johnsongrass control. Johnsongrass control following treatment with asulam at 3.7 kg ai ha−1 was not improved by tank mixtures with the residual herbicides atrazine, metribuzin, pendimethalin, and terbacil compared with asulam applied alone. Johnsongrass injury symptoms appeared sooner when asulam was applied in mixtures with either DSMA or MSMA, but johnsongrass control 4 wk after treatment was similar to asulam applied alone. As a result of the johnsongrass control obtained with early POST treatments of asulam applied alone, cane and sugar yields were increased by 56 and 58%, respectively, when compared with the weedy check. Additional cane and sugar yield increases were not obtained by any of the asulam mixtures because johnsongrass control was not improved. Asulam applied again in May to johnsongrass regrowth improved late-season control in two of the three studies over a single early POST application, but cane and sugar yields were not increased.

Greenhouse experiments were conducted in 1989 at Stoneville, MS to evaluate the efficacy of fluridone and MSMA applied at 0.3 and 1.0 kg ai ha-1, respectively, either alone or in combination and with or without 0.1 M ammonium sulfate on purple nutsedge. The herbicides were applied at 19 L ha-1 in an oil-water, invert emulsion (low-volume) and at 187 L ha-1 in water with a nonionic surfactant (0.25% v/v) (high-volume). Purple nutsedge control with both herbicides alone or in combination was greater with the low-volume than with the high-volume application. Addition of MSMA to fluridone, or of ammonium sulfate to fluridone plus MSMA did not enhance purple nutsedge control over fluridone alone applied in low volume. The addition of ammonium sulfate to fluridone alone applied in low volume reduced purple nutsedge control.

Kikuyugrass is an invasive, perennial weed of turf-grass in California. Currently, complete renovation of infested turf is the most practical means of control. A less disruptive method was needed to reduce the competitive ability of kikuyugrass while allowing the regrowth of desirable turf species. Treatment with MSMA, triclopyr, and quinclorac did not control kikuyugrass as single applications, but when applied at 4- to 5-wk intervals over a 5-mo period, kikuyugrass was reduced. Sequential applications of two-way combinations of these herbicides in 1991 resulted in reductions of kikuyugrass from 80% to less than 1% of the sward.

Cotton yield response was evaluated in 1987, 1988, and 1989 when weeds were managed with preemergence fluometuron [none (0%), band (50%), or broadcast (100%) surface coverage], cultivation (none, one, two, or three times), and postdirected fluometuron + MSMA. Weed densities (primarily prickly sida, morningglories, and hemp sesbania) varied widely among years and were directly related to early season rainfall. Postdirected herbicide application or cultivation(s) had little effect on weed density. The use of a banded fluometuron application reduced weed biomass 28 to 47%. A further decrease was observed when preemergence fluometuron was increased from banded to broadcast coverage. Seed cotton yields were low with no preemergence fluometuron. Banded fluometuron and at least one cultivation had yields similar to broadcast fluometuron only. Cotton yields were related to weed density and weed biomass in a hyperbolic relationship. Low weed densities caused more yield loss per unit weed density than higher densities.

Sequential applications of preemergence (PRE) and postemergence (POST) herbicides were applied over a two-year period for large crabgrass and goosegrass control in common bermudagrass. Large crabgrass control was better when prodiamine at 0.3 kg ai ha−1 or oryzalin at 0.8 kg ai ha−1 were applied in late February, and followed by MSMA at 1.1 kg ai ha−1 in June than when prodiamine (0.8 kg ha−1) or oryzalin (2.4 kg ha−1) were applied at recommended rates. Goosegrass control was better when prodiamine was applied at 0.3 kg ha−1 followed by MSMA plus metribuzin at 2.2 + 0.1 kg ai ha−1, or when oryzalin was applied at 1.7 kg ha−1followed by MSMA plus metribuzin at 1.1 + 0.1 kg ha−1 than when prodiamine was applied at 0.8 kg ha−1 or oryzalin was applied at 3.3 kg ha−1. There was no increase in goosegrass control when diclofop was applied in sequence after prodiamine or oryzalin compared to diclofop alone. POST applications of diclofop, MSMA, and MSMA plus metribuzin did not injure common bermudagrass more severely when applied to plots previously treated with prodiamine and oryzalin than with POST herbicides alone.

Field studies were conducted to determine if metribuzin–diclofop combinations could provide selective control of mature goosegrass in common bermudagrass turf. In two field trials, diclofop at 1.7 kg ai/ha provided 19% control of mature goosegrass at 7 wk after treatment (WAT), whereas metribuzin at 0.28 or 0.56 kg ai/ha controlled 30 and 53%, respectively. When diclofop at 1.7 kg/ha was combined with metribuzin at 0.28 or 0.56 kg/ha, goosegrass control increased to 68 and 90%, respectively. That degree of mature goosegrass control with a single application of metribuzin at 0.56 kg/ha plus diclofop at 1.7 kg/ha was equivalent to metribuzin at 0.56 kg/ha plus MSMA at 2.2 kg ae/ha followed by MSMA at 2.2 kg/ha 1 wk later. The metribuzin–diclofop combination injured common bermudagrass turf less than or equivalent to the metribuzin–MSMA combination. The injury was transitory; at 3 WAT, none of the treatments injured common bermudagrass.