Studies were conducted in 2019 and 2020 in Lewiston, NC, to determine the crop response of 4-hydroxyphenylpyrivate dioxygenase (HPPD)-resistant cotton to isoxaflutole (IFT) and other cotton herbicides as part of a cotton weed management program that included herbicides applied preemergence, early postemergence (EPOST), and mid-postemergence (MPOST). IFT was applied PRE at 105 g ha−1 alone and in various combinations with acetochlor, diuron, fluometuron, fluridone, fomesafen, pendimethalin, and pyrithiobac. EPOST treatments included IFT at 53 or 105 g ha−1 alone or in combination with glyphosate or glufosinate, or dimethenamid-P + glufosinate. Glyphosate + glufosinate was applied MPOST to all treatments except the nontreated control. Cotton injury from IFT applied PRE was minimal (0% to 3%). Injury following EPOST application of dimethenamid-P + glufosinate ranged from 3% to 5% and 6% to 9% in 2019 and 2020, respectively. In both years, injury from IFT applied PRE followed by IFT applied EPOST never exceeded injury from IFT applied PRE followed by dimethenamid-P + glufosinate. Isoxaflutole applied PRE followed by IFT applied EPOST at 105 g ha−1 resulted in 0% to 2% cotton injury, indicating that IFT can be applied either PRE or EPOST with minimal risk to cotton. Late-season cotton height and cotton lint yield were not affected by any herbicide treatment. The experimental HPPD-resistant cotton cultivar was minimally injured by IFT applied PRE and EPOST, it tolerated standard cotton herbicides, and yield loss was not observed. Given these results, HPPD-resistant cotton and IFT may be integrated into cotton weed management systems with minimal risk for cotton injury and provide an additional effective mechanism of action for managing troublesome weeds in cotton.

BASF Corp. has developed p-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor–resistant cotton and soybean that will allow growers to use isoxaflutole in future weed management programs. In 2019 and 2020, a multi-state non-crop research project was conducted to examine weed control following isoxaflutole applied preemergence alone and with several tank-mix partners at high and low labeled rates. At 28 d after treatment (DAT), Palmer amaranth was controlled ≥95% at six of seven locations with isoxaflutole plus the high rate of diuron or fluridone. These same combinations provided the greatest control 42 DAT at four of seven locations. Where large crabgrass was present, isoxaflutole plus the high rate of diuron, fluridone, pendimethalin, or S-metolachlor or isoxaflutole plus the low rate of fluometuron controlled large crabgrass ≥95% in two of three locations 28 DAT. In two of three locations, isoxaflutole plus the high rate of pendimethalin or S-metolachlor improved large crabgrass control 42 DAT when compared to isoxaflutole alone. At 21 DAT, morningglory was controlled ≥95% at all locations with isoxaflutole plus the high rate of diuron and at three of four locations with isoxaflutole plus the high rate of fluometuron. At 42 DAT at all locations, isoxaflutole plus diuron or fluridone and isoxaflutole plus the high rate of fluometuron improved morningglory control compared to isoxaflutole alone. These results suggest that isoxaflutole applied preemergence alone or in tank mixture is efficacious on a number of cross-spectrum annual weeds in cotton, and extended weed control may be achieved when isoxaflutole is tank-mixed with several soil-residual herbicides.

Atrazine offers growers a reliable option to control a broad spectrum of weeds in grain sorghum production systems when applied PRE or POST. However, because of the extensive use of atrazine in grain sorghum and corn, it has been found in groundwater in the United States. Given this issue, field experiments were conducted in 2017 and 2018 in Fayetteville and Marianna, Arkansas, to explore the tolerance of grain sorghum to applications of assorted photosystem II (PSII)-inhibiting herbicides in combination with S-metolachlor (PRE and POST) or mesotrione (POST only) as atrazine replacements. All experiments were designed as a factorial, randomized complete block; the two factors were (1) PSII herbicide and (2) the herbicide added to create the mixture. The PSII herbicides were prometryn, ametryn, simazine, fluometuron, metribuzin, linuron, diuron, atrazine, and propazine. The second factor consisted of either no additional herbicide, S-metolachlor, or mesotrione; however, mesotrione was excluded in the PRE experiments. Crop injury estimates, height, and yield data were collected or calculated in both studies. In the PRE study, injury was less than 10% for all treatments except those containing simazine, which caused 11% injury 28 d after application (DAA). Averaged over PSII herbicide, S-metolachlor–containing treatments caused 7% injury at 14 and 28 DAA. Grain sorghum in atrazine-containing treatments yielded 97% of the nontreated. Grain sorghum receiving other herbicide treatments had significant yield loss due to crop injury, compared with atrazine-containing treatments. In the POST study, ametryn- and prometryn-containing treatments were more injurious than all other treatments 14 DAA. Grain sorghum yield in all POST treatments was comparable to atrazine, except prometryn plus mesotrione, which was 65% of the nontreated. More herbicides should be evaluated to find a comparable fit to atrazine when applied PRE in grain sorghum. However, when applied POST, diuron, fluometuron, linuron, metribuzin, propazine, and simazine have some potential to replace atrazine in terms of crop tolerance and should be further tested as part of a weed control program across a greater range of environments.

Weed control in corn traditionally has relied on atrazine as a foundational tool to control problematic weeds. However, the recent discovery of atrazine in aquifers and other water sources increases the likelihood of more strict restrictions on its use. Field-based research trials to find atrazine alternatives were conducted in 2017 and 2018 in Fayetteville, AR, by testing the tolerance of corn to PRE and POST applications of different photosystem II (PSII) inhibitors alone or in combination with mesotrione or S-metolachlor. All experiments were designed as a two-factor factorial, randomized complete block, with the two factors being (1) PSII-inhibiting herbicide and (2) the herbicide added to create the mixture. The PSII-inhibiting herbicides were prometryn, ametryn, simazine, fluometuron, metribuzin, linuron, diuron, atrazine, and propazine. The second factor consisted of either no additional herbicide, S-metolachlor, or mesotrione. Treatments were applied immediately after planting in the PRE experiments and to 30-cm–tall corn for the POST experiments. For the PRE study, low levels of injury (<15%) were observed at 14 and 28 d after application and corn height was negatively affected by the PSII-inhibiting herbicide applied. PRE-applied fluometuron- and ametryn-containing treatments consistently caused injury to corn, often exceeding 5%. Because of low injury levels caused by all treatments, crop density and yield did not differ from that of the nontreated plants. For the POST study, crop injury, relative height, and relative yield were affected by PSII-inhibiting herbicide and the herbicide added. Ametryn-, diuron-, linuron-, propazine-, and prometryn-containing treatments caused at least 25% injury to corn in at least 1 site-year. All PSII-inhibiting herbicides, except metribuzin and simazine when applied alone, caused yield loss in corn when compared with atrazine alone. Diuron-, linuron-, metribuzin-, and simazine-containing treatments applied PRE and metribuzin- and simazine-containing treatments applied POST should be investigated further as atrazine replacements.

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.

Extension workers are sensing pressure to use soils information and chemical characteristics data to guide farmers in selecting pesticides least prone to leach into groundwater. Our objective was to estimate differences in herbicide migration to groundwater under conditions typical for the Southeast Coastal Plain, and to consider how a farmer might be advised to use such knowledge in selecting herbicides. We used a simple computer code for microcomputers to predict persistence and migration of 17 herbicides through a hypothetical, coarse-textured soil typical of the Southeast Coastal Plain. Appropriate herbicides were selected for several common crop-weed problems, such as sicklepod in soybean and Palmer amaranth in corn. Groundwater was assumed to be 3.15 m below the soil surface. Herbicides selected covered a broad range of half-lives and organic carbon partition coefficients. Only after the first-order degradation rate constant was reduced by a factor of five did predicted soil water concentrations of several herbicides at the groundwater interface reach normal detection limits. Still, predicted concentrations were below the level established for health effects advisory purposes. Due to the large number of uncertainties and the inability to estimate practical benefits, we conclude that data relating to soil and herbicide characteristics cannot be used at this time to override cost effectiveness, efficacy, and other factors normally considered by farmers and Extension professionals in herbicides for weed control.

One and two postemergence (POE) applications of the butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid} or sethoxydim (2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} following preemergence (PRE) application of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} were compared to a preplant-incorporated (PPI) application of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] or pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] plus fluometuron PRE or pendimethalin plus fluometuron PRE for annual grass control in cotton (Gossypium hirsutum L.) and net economic return to land, overhead, and management. One POE application of either fluazifop or sethoxydim following fluometuron PRE resulted in greater control of a high population of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash. # BRAPP] and greater yield and net return than a PPI application of trifluralin or pendimethalin plus fluometuron PRE. A second application of fluazifop or sethoxydim increased late-season control but did not increase yield or net return. In a high population of large crabgrass (Digitaria sanguinalis L. # DIGSA), fluometuron PRE plus two POE applications of fluazifop or sethoxydim resulted in grass control, lint yield, and net return similar to trifluralin or pendimethalin PPI plus fluometuron PRE. No differences in grass control, crop response, or net return were noted between PPI application of trifluralin or pendimethalin. Control of broadleaf signalgrass and large crabgrass with pendimethalin plus fluometuron PRE was less than with pendimethalin PPI plus fluometuron PRE. In fields with a low population of large crabgrass, fall panicum (Panicum dichotomiflorum Michx. # PANDI), and goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], fluometuron PRE provided excellent season-long control. No benefits were obtained from addition of a grass herbicide. No treatments affected cotton maturity or fiber quality.

Johnsongrass control systems that included commercially available corn herbicides applied to crop sequences of continuous corn or corn–cotton–corn rotation were evaluated over a 3-yr period at the Texas Agricultural Experiment Station in Burleson County. Herbicide treatments evaluated were EPTC + R-25788 applied preplant incorporated (PPI); metolachlor applied preemergence (PRE); nicosulfuron applied postemergence (POST); and the combination of metolachlor PRE and glyphosate POST applied after corn harvest. Weed control practices applied to plots planted to cotton in the second growing season provided excellent johnsongrass control (≈ 95%). Visual control ratings indicated that nicosulfuron provided the best johnsongrass control (> 80%) among the herbicides evaluated all three years. Metolachlor and glyphosate combinations provided acceptable johnsongrass control the third year of the experiment in both cropping sequences. Corn grain yield and johnsongrass control were best in cotton-rotated plots. The highest returns observed in continuous corn were from either nicosulfuron or the combination of metolachlor and glyphosate. Net returns for all control systems in corn–cotton–corn rotated plots were greater than the weedy check and were equivalent to the lead systems in continuous corn.

The comparative susceptibility of weedy okra [Abelmoschus esculentus (L.) Moench.] and three commercial okra cultivars (′Dwarf Green Long Pod′, ‘Clemson Spineless', and ‘White Velvet′) to six preemergence herbicides was evaluated in the greenhouse. Okra can be controlled in cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] fields with appropriate preemergence herbicide use. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] completely controlled okra at 0.2 to 0.8 kg/ha. Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] at 0.9 to 1.8 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 1.2 to 2.4 kg/ha controlled okra, but at the 0.6 kg/ha rate cyanazine did not control wild okra and fluometuron at 0.45 kg/ha did not completely control any cultivar. Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] bleached the cotyledons and young leaves of okra, but gave 50% or less control even at 2.4 kg/ha. Both the weedy and commercial okras were completely resistant to trifluralin (α,α,α-trifluoro-2,6-dinitro -N,N-dipropyl-p-toluidine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] but higher rates of these herbicides affected okra growth.

Four-year cropping sequences of continuous cotton, cotton-soybeans-soybeans-cotton, continuous soybeans, soybeans-grain sorghum-soybeans-grain sorghum, and cotton-rice-cotton-rice were treated each year with high and low levels of herbicides to control johnsongrass. High levels of herbicide were necessary to control johnsongrass in continuous cotton, cotton-soybeans-soybeans-cotton, continuous soybeans, and the soybeans-grain sorghum rotation. Johnsongrass was not eradicated, however, after 4 years of cropping sequences with high herbicide inputs. Both low and high levels of herbicide coupled with water management required for rice production controlled johnsongrass and prevented rice yield reductions.

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.

Eleven herbicide systems were evaluated from 1981 to 1983 for cotton (Gossypium hirsutum L. ‘Stoneville 825’) planted no-till directly into cover crops or winter fallow and for cotton planted following conventional tillage. Herbicide systems consisted of paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) or glyphosate [N-(phosphonomethyl)glycine] and/or residual herbicides applied prior to crop emergence. Some systems also included early postemergence or postemergence-directed applications. Cover crops were crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth.), and rye (Secale cereale L.). Soil cover in fallow treatments was comprised mainly of cotton stalk residue. Conventional tillage and seedbed preparation included fall moldboard plowing and spring disking/smoothing. Treatments were maintained in the same site each year. Order of cover crop susceptibility to herbicides applied prior to crop emergence was rye>clover>vetch. In 1981, all residual treatments except cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} alone prior to crop emergence provided better than 80% control of annual weeds. In subsequent years only systems that included applications prior to crop emergence and postemergence-directed herbicides provided acceptable control. From 1981 to 1983, annual grasses increased 20- to 100-fold for systems in which control was poor. Weed control was generally superior in conventional tillage. Vetch adversely affected cotton stands in all 3 yr. Also, in 1982, reduced cotton stands resulted from cyanazine treatments applied prior to crop emergence in clover, vetch, and fallow. Cotton yields were affected by cover dessication, annual weed control, and cotton stands. Buildup of annual weeds reduced yields to near zero for some treatments in 1983.

The residual effect of three cotton (Gossypium hirsutum L.) herbicide programs, including the use of no herbicides, a minimum program consisting of fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl] urea} and MSMA (monosodium salt of methylarsonic acid), and an intensive program consisting of trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine], fluometuron, MSMA, and linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea], were evaluated from 1976 to 1982. Herbicide injury to wheat (Triticum aestivum L.) and hairy vetch (Vicia villosa Roth.) on three soils showed carryover effects in the following sequence: Sharkey silty clay > Dundee silt loam > Loring silt loam. The intensive program was the most injurious on the Sharkey silty clay. The effects of the two herbicide programs were nearly equal on the Dundee and Loring silt loams. Possible replacement crops for cotton, such as grain sorghum [Sorghum bicolor (L.) Moench.] and corn (Zea mays L.) suffered the least damage from carryover; rice (Oryza sativa L.), soybeans [Glycine max (L.) Merr.] and cucumber (Cucumis sativis L.) suffered severe damage. Greenhouse bioassays generally confirmed field results, and fluometuron appeared to be the major component of carryover.

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.

Because adsorption is a major factor controlling herbicide persistence, activity, and mobility in soils, an extensive literature exists on the measurement of this process. The adsorption data are usually fitted to the Freundlich equation, but attempts to interpret this equation theoretically have had only limited success. A meaningful thermodynamic interpretation of the Freundlich equation can be developed using a proposed standard state for adsorbed herbicide, which assumes that soil organic matter forms a solid solution with the herbicide. When herbicide vapor pressures and aqueous solubilities are taken into account, the losses in free energy of different herbicides, on adsorption onto wetted soil surfaces, are shown to be similar to each other and are slightly less than the loss on absorption to the solid herbicides themselves. The Freundlich exponent is related in a simple way to the decreasing energy of available soil sites as the amount of herbicide adsorbed increases, but this change is relatively small over the range of concentrations used in adsorption experiments. Sample results are given for six triazine, three urea, and one uracil herbicides.

Preliminary greenhouse studies indicated the presence of a synergistic interaction between low rates of fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] in combination with linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea] or chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea]. In a 3-yr field study, moderate injury of cotton (Gossypium hirsutum L. ‘Stoneville 213’) with no yield reduction was observed with fluometuron or diuron at 1.68 and 1.12 kg/ha, respectively, but higher rates (5.04 and 3.36 kg/ha, respectively) caused injury and yield reductions. Soybean [Glycine max (L.) Merr. ‘Hill’] injury ratings during the second year indicated a synergistic interaction between residue from fluometuron at 5.04 kg/ha combined with linuron at 2.48 kg/ha or chlorbromuron at 3.85 kg/ha, and from diuron at 3.36 kg/ha combined with linuron at 2.48 kg/ha. These interactions were not apparent in soybean yield data. Soybean injury the third year ranged from 30 to 60% with single or repeated applications of linuron or chlorbromuron, although yields were not affected. Residual fluometuron and diuron from 2 yr of application at 5.04 and 3.36 kg/ha, respectively, injured soybeans, but did not reduce yields. Significant synergistic interactions were observed through injury and yield measurements after two annual applications of fluometuron at 5.04 kg/ha combined with linuron or chlorbromuron. A synergistic interaction was detected in soybean yields with chlorbromuron at 3.85 kg/ha preceded by two annual applications of diuron at 3.36 kg/ha. Such interactions may occur under field conditions, but are unlikely to be economically significant. Chemical analysis indicated little evidence of accumulation, even with repeated application of fluometuron or diuron at 5.04 and 3.36 kg/ha, respectively.

Field experiments were conducted in 1982 and 1983 in cotton (Gossypium hirsutum L.) to evaluate alternatives in grass weed management programs with the use of postemergence herbicides and to assess the economic potential for incorporating the new over-the-top grass weed herbicides into total cotton production practices. Twelve weed management systems using the grass herbicides sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} were compared to six standard systems. Differences in cotton production costs among the 18 systems were due to cost differences in total weed management. Equal or greater net return values were obtained when over-the-top herbicides followed fluometuron {N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl)urea} preemergence or when these materials were applied twice compared to the over-the-top materials used in conjunction with trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] preplant incorporated or with directed postemergence materials. High net returns were the result of both high seed cotton yields and low total production costs.

Four cultivations of cotton [Gossypium hirsutum L. ‘Stoneville 213′] alone failed to reduce green weed biomass or increase seed cotton yields above that of the no weed control treatment, and thus resulted in a negative net return (−200 to −450 $/ha) all 4 yr. Two cultivations plus two hand-hoeings reduced green weed biomass and increased seed cotton yields 3 out of 4 yr, thus a positive net return was produced for 3 yr ranging from 300 to 640 $/ha. Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] alone was the most effective treatment in reducing green weed biomass and increasing seed cotton yields, and produced the highest net return, 280 to 420 $/ha for the 4-yr period. The addition of cultivation did not improve the fluometuron treatment. However, diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea)] required three supplementary cultivations to equal the single fluometuron treatment. Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) plus three cultivations did not equal the single fluometuron treatment, although a positive net return was obtained every year. The addition of trifluralin to fluometuron also failed to improve weed control or net return over that of fluometuron alone.

Field experiments were established to evaluate coffee senna control in cotton with registered PRE, early POST-directed (EPD), and late POST-directed (LPD) herbicides and with pyrithiobac applied PRE and early POST. Fluometuron and norflurazon applied PRE controlled coffee senna 87 and 65%, respectively, 6 wk after planting (WAP). Methazole applied EPD controlled coffee senna 96% 2 wk after application, whereas fluometuron and MSMA applied EPD controlled 70 and 16%, respectively. LPD applications of cyanazine, diuron, and prometryn averaged only 45% control 8 WAP. MSMA applied LPD controlled coffee senna only 12%. Fluometuron and norflurazon applied PRE followed by methazole applied EPD and cyanazine applied LPD controlled coffee senna 98 and 99% 6 WAP, respectively. PRE, early POST, and PRE followed by early POST applications of pyrithiobac controlled coffee senna 88, 89, and 95% 6 WAP, respectively. Seed cotton yields were similar to weed-free cotton with all treatments except MSMA applied EPD and the LPD treatments, all of which provided unacceptable (12 to 49%) control 8 WAP.

Soybeans [Glycine max (L.) Merr.] are often the replacement crop when cotton (Gossypium hirsutum L.) is abandoned because of stand failure in the southern United States. Injury from cotton herbicides may be reduced if the soybean planting is delayed more than 4 weeks after cotton planting or if the original herbicide-treated area is fully tilled and a new seedbed formed. Planting delay intervals were compared with five cotton preemergence herbicides on Calloway silt loam at one location. Seedbed-preparation methods were included in a similar experiment at two locations on Sharkey silty clay. Herbicides compared were fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea], norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H)-pyridazinone], cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, perfluidone {1,1,1-trifluoro-N-[2-methyl-4-phenylsulfonyl)phenyl] methanesulfonamide}, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, and diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Seedbeds compared were no-till and conventional (fully tilled). Soybean planting delays after cotton planting were 20, 29, and 56 days (first year), and 15 and 29 or 15 and 30 days (second year). We found in the 2-yr studies that fluridone severely damaged soybeans both years. Fluometuron and diuron also caused damage the second year when we experienced wet, cool conditions in the spring. Most injury occurred on the clay, with yield reductions occurring even after the 30-day delay. Norflurazon was most injurious at this location. The no-tillage planting method resulted in the least herbicide injury on the silt loam and the conventional tillage method was better on the clay. Detailed studies with fluometuron under incubation conditions showed that degradation was inhibited most by low temperatures and high soil moisture.