Browsing by Author "Vencill, William K."
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- Field and laboratory investigations on the efficacy, selectivity, and action of the herbicide clomazoneVencill, William K. (Virginia Polytechnic Institute and State University, 1988)Clomazone is a recently introduced herbicide for the selective control of grass and broadleaf weeds in soybeans. Field studies were conducted in full-season no-till soybeans to determine the efficacy of clomazone as a preplant and preemergence herbicide. Clomazone applied preemergence provided large crabgrass (Digitaria sanguinalis L.) control equivalent to that of oryzalin applied preplant or preemergence and provided better control of several broadleaf weeds. Control from preplant applications of clomazone was not adequate. Preemergence and preplant incorporated applications of clomazone were compared in conventionally-tilled soybeans. Clomazone efficacy at two depths of incorporation was also investigated. Clomazone applied preemergence generally provided control of large crabgrass and several broadleaf weed species equivalent to preplant incorporated applications. The addition of imazaquin or chlorimuron plus linuron improved smooth pigweed (Amaranthus hybridus L.) control over that provided by clomazone alone. These combinations generally did not improve large crabgrass, jimsonweed (Datura stramonium L.), and common lambsquarters (Chenopodium album L.) control over that of clomazone alone. Shallow incorporation (4 cm) of clomazone provided better weed control than deep incorporations (8 cm). Studies were conducted to evaluate efficacy and to quantify volatilization of three clomazone formulations (emulsifiable concentrate, wettable powder, and a microencapsulated formulation) following soil application. Samples were collected at the first, second, and tenth day after clomazone application. The three clomazone formulations provided control of large crabgrass. Clomazone volatilization was greatest 24 h after application from the emulsifiable concentrate and wettable powder formulations and declined at the second and tenth day after application. Volatilization from the microencapsulated formulation was lower than the other two formulations at all sampling times. Clomazone volatilization was greater from preemergence than preplant incorporated applications. Differential selectivity studies were initiated to determine the absorption, translocation, and metabolism of clomazone in tolerant soybean and smooth pigweed and susceptible redroot pigweed and livid amaranth exposed to foliar and root applied clomazone. Redroot pigweed and livid amaranth absorbed more clomazone through the roots than soybean and smooth pigweed. Absorption of foliar-applied clomazone was limited in all species. Of the clomazone absorbed in all species, most was translocated to the leaf tissue. Two metabolites of clomazone were found. One was determined to be a GS-clomazone conjugate. Differences in clomazone metabolism among species examined were not found. Growth and physiological responses of a normal hybrid ('DeKalb XL67'), a dwarf mutant, and an albino mutant of corn (Zea mays L.) to clomazone and interactions of gibberellin with clomazone on normal corn were examined. The dwarf mutant displayed greater tolerance to clomazone than normal corn. Growth measurements suggested that gibberellin was antagonistic with clomazone.
- Triazine resistance in Chenopodium album and Amaranthus hybridus in VirginiaVencill, William K. (Virginia Polytechnic Institute and State University, 1986)Studies were conducted to determine the distribution of s-triazine resistant biotypes of common lambsquarters (Chenopodium album L.) and smooth pigweed (Amaranthus hybridus L.) in Virginia. Collections of seed were made from suspected triazine-resistant biotypes of common lambsquarters and smooth pigweed from counties in Virginia which had reported having triazine resistance problems. Triazine resistance was confirmed by measuring chlorophyll fluorescence in the presence of atrazine. For further confirmation of triazine resistance in collected common lambsquarters and smooth pigweed biotypes, greenhouse testing of whole plants and a sinking leaf disc assay were performed. Cross-resistance to another s-triazine, as-triazine, and substituted urea herbicide was also determined for s-triazine-resistant biotypes. These studies have shown triazine- resistant smooth pigweed to be present in 19 counties and common lambsquarters to be present in 8 counties in Virginia. s-Triazine resistant biotypes were found to be resistant to another s-triazine and as-triazine herbicide, but were susceptible to the substituted urea herbicide. Additional studies were initiated to determine the effects of different temperature regimes on triazine-resistant and -susceptible biotypes of common lambsquarters and smooth pigweed from different geographical locations. These studies were conducted at the North Carolina State University Phytotron facility in controlled environment growth chambers. Triazine-resistant common lambsquarters biotypes from Virginia, Maryland, and Switzerland as well as a smooth pigweed biotype from Virginia were examined. Triazine-susceptible biotypes of common lambsquarters and smooth pigweed were included as controls. Shoot height, weight, chlorophyll a and b content, and whole leaf fatty acid content of common lambsquarters and smooth pigweed were determined at 18°/14° C, 26°/22° C, and 36°/26° C. Measurements of shoot height were made at 30 and 63 days after planting. The shoot weight, chlorophyll a and b content, and fatty acid content was determined from plants harvested at 63 days after planting. These data indicate common lambsquarters biotypes from different geographical regions exhibited a differential response to temperature. There was no difference between triazine-resistant and -susceptible biotypes in response to temperature. Differences were detected between triazine-resistant smooth pigweed biotypes which indicated that the susceptible biotypes were more vigorous as indicated by shoot height and weight at lower temperatures than triazine-resistant biotypes of smooth pigweed.