Antidotes were evaluated for their ability to prevent corn and sorghum injury caused by imazaquin. Plant injury was reduced in both preemergence and early postemergence imazaquin applications. Naphthalic anhydride (NA) seed treatment was the most consistent compound in reducing the imazaquin injury. Seed treatment with CGA 92194 or flurazole also gave injury protection to corn and sorghum, while soil treatment with dichlormid provided the least protection from imazaquin injury. Treatment with the antidotes did not affect the acetolactate synthase (ALS) (EC4.1.3.18) activity in corn or sorghum tissues. Imazaquin treatments decreased extractable ALS activity but this decrease was eliminated, partially or totally, by the most effective antidotes. Antidote treatments had little effect on absorption and distribution of 14C in plants growing in soil treated with 14C-imazaquin. Antidote treatments increased the metabolism of 14C-imazaquin to both soluble and unextractable 14C after 24 h of exposure. The increased rate of imazaquin conversion to less toxic metabolites when antidotes were used resulted in a reduction in imazaquin injury to corn and sorghum.

Experiments were conducted to monitor the dissipation of imazaquin and imazethapyr applied to the soil surface under conventional and no-tillage conditions. Imazaquin or imazethapyr dissipation rate was similar in no-tillage in 1985 and 1986. Dissipation of the herbicides under conventional tillage conditions varied. Imazaquin dissipation occurred 2.4 times faster in 1986 than in 1985. Imazethapyr dissipation was 3.5 times faster in 1986 than in 1985. Corn planted without tillage (no-till) was injured in 1986 where 210 or 280 g ha-1 of imazaquin or 105 g ha-1 of imazethapyr had been applied the previous year to conventionally tilled soybeans, but injury was not evident where these herbicides had been applied to no-tillage soybeans. Corn injury was evident 2 wk after planting in 1987 but yields were not reduced.

Studies were conducted to investigate the uniformity of epicuticular wax deposition on leaf blades of johnsongrass. Johnsongrass leaves grown under drought stress had greatly increased epicuticular wax weights compared to leaves from plants with adequate moisture, but relative humidity (95% vs. 40 ± 5%) had little effect on wax deposition. Wax weights decreased as leaves matured. Sections of lower leaf surfaces of young johnsongrass leaves tended to have more wax than sections of upper leaf surfaces, but weights were nearly equal on upper vs. lower leaf surfaces of older leaves. The narrow side of asymmetrical johnsongrass leaf blades often had more wax per unit area than the wide side. The area over the midvein contained more wax per unit area than either the narrow or wide side of the leaf blade. Greatest wax concentrations on individual leaves were over the midvein area near the leaf apex. Leaf blades of johnsongrass had more wax per unit area than leaves of corn or grain sorghum.

Antidotes were evaluated under greenhouse conditions for their ability to prevent injury to corn and sorghum from imazethapyr. Corn was more tolerant to imazethapyr and more effectively protected from imazethapyr toxicity than sorghum. Naphthalic anhydride (NA)3, CGA 92194, or flurazole treatment of corn seed reduced plant injury from preemergence applications of imazethapyr. Corn injury from postemergence applications of imazethapyr was decreased by seed treatment with NA or CGA 92194. Sorghum injury from preemergence applications of imazethapyr was not reduced by seed treatment with the antidotes. NA treatment of sorghum seed was the most effective antidote treatment for decreasing injury from postemergence applications of imazethapyr but the level of sorghum protection was much less than that achieved with corn. Corn seedlings grown from NA-treated and untreated seed absorbed equal amounts of 14C into the roots from nutrient solution containing 14C-imazethapyr. The NA-treated corn plants translocated less of the absorbed 14C to the shoots than the untreated plants. NA treatment of corn seeds increased the rate of imazethapyr conversion to soluble metabolites 2-and 10-fold in the corn seedling roots and shoots, respectively. The increased rate of imazethapyr metabolism in corn following NA seed treatment may be responsible for the protection from imazethapyr toxicity.

Experiments were conducted in 1985 to 1987 to evaluate the effects of conventional and no-tillage systems on the weed control provided by clomazone applied preemergence in soybeans. The persistence of clomazone in soil of the two tillage systems was also determined. Increasing the clomazone rate from 0.8 to 1.4 kg/ha did not increase weed control. Clomazone controlled 80% or more of jimsonweed, velvetleaf, and giant foxtail. Common cocklebur control ranged from about 50 to 70% in no-till and from 80 to 90% in conventional tillage. Generally, soybean pods/plant and yields were lower from clomazone treatments than from handweeded treatments due to inadequate common cocklebur control. Over 40% of the clomazone applied did not reach the soil surface; it was either intercepted by wheat straw, volatilized, or both. Clomazone persisted longer in conventional tillage than in no-tillage in. However, in 1986, clomazone was equally persistent in the two tillage systems. The half-life of clomazone was 34 and 6 days in 1985 in conventional and no-tillage, respectively, and in 1986, 18 and 16 days in conventional and no-tillage, respectively. Significant clomazone concentrations were not found below 10 cm in the soil profile. Corn planted without tillage (no-till) approximately 1 yr after clomazone application was not injured and yields were not reduced due to prior clomazone use.

Experiments were conducted on a Cedarbluff silt loam and a Cecil sandy loam to determine dissipation of imazaquin and imazethapyr as influenced by burning small-grain straw and tillage prior to soybean planting. Corn bioassay detection limits for imazaquin and imazethapyr in the Cedarbluff silt loam were 2.5 to 30 and 5 to 40 ppbw, respectively. Bioassay detection limits for imazaquin and imazethapyr in the Cecil sandy loam were 2.5 to 20 and 10 to 40 ppbw, respectively. Imazaquin and imazethapyr activity was not detectable in soil by 110 to 152 d after treatment. Imazethapyr dissipation was not affected by burning or tillage in the Cedarbluff silt loam and dissipated more slowly in 1989 than imazaquin. Imazaquin dissipation in the Cedarbluff silt loam in 1988 was slower in burned plots than in nonburned plots but was not affected by burning in 1989. No differences were observed between imazaquin and imazethapyr dissipation in the Cecil sandy loam and neither burning or tillage influenced their rate of dissipation in either year. No-till-planted cotton was injured at both locations by imazaquin and imazethapyr that had been applied the previous year.

Monoculture velvetleaf had greater dry weight, growth rate, leaf area index, and height than velvetleaf grown in association with conventional or no-tillage corn. Velvetleaf planted 5 weeks after corn had significantly lower dry weight, leaf area index, and height compared to velvedeaf planted at the same time as corn. The combination of interference from corn and delayed planting caused a significant reduction in velvetleaf population at the end of the season, delayed the date of 50% velvetleaf flowering, increased the number of days required for 50% flowering, and reduced the number of capsules per plant. Velvetleaf dry weight/hectare and leaf area index increased as plant population increased. Velvetleaf dry weight, leaf area, capsules, and seed/plant decreased as plant density increased. There were no differences in vegetative or reproductive growth between velvetleaf grown in conventional or no-tillage areas.

The growth of two mallow family weeds, velvetleaf and prickly sida, was inhibited 50% when seedlings were treated with less than 200 g ai/ha of thidiazuron. Spurred anoda was unaffected by treatment with up to 1120 g/ha of thidiazuron. Cotton, okra, and hibiscus, all in the mallow family, also were susceptible to thidiazuron treatment. Leaf development in 2-week-old cotton seedlings was inhibited 20% by less than 35 g/ha thidiazuron as were seedling okra and hibiscus. Plants of all these susceptible species were more resistant when grown for 2 months before treatment. Seedlings of soybean displayed localized injury after treatment, but plant height, biomass, and seed production were not significantly affected 10 weeks after treatment with up to 1120 g/ha thidiazuron. Seedlings of corn appeared unaffected by treatment with up to 1120 g/ha thidiazuron.