Philip A. Banks

Carrier Volume Affects Herbicide Activity in Simulated Spray Drift Studies

Abstract: Field studies were conducted to determine if varying carrier volume proportionally with herbicide dosage, thus maintaining constant herbicide concentration in the carrier, would change the response of sweet corn to glyphosate and of cotton to 2,4-D when compared with using a constant carrier volume where herbicide concentration would vary and be more dilute. For all the parameters measured, more sweet corn injury occurred if the concentration of glyphosate was constant in all volumes of spray. The glyphosate no-effect level for sweet corn was determined to be 0.046 kg/ha when using the variable carrier volume but was over four times greater (0.185 kg/ha) when applied at the constant carrier volume of 281 L/ha. Cotton response to 2,4-D was similar, with the constant herbicide concentration in the carrier at the lower volumes causing greater injury. The response of seed cotton yield was not different when comparing constant to variable carrier volume. The highly sensitive growth stage of cotton at the time of application (bud formation before blooming) may explain this result. These studies demonstrate the need to use carrier volumes that are proportional to the herbicide dosage, thus maintaining constant herbicide concentration in the carrier, when conducting simulated herbicide drift research. Failure to do so could underestimate the potential for injury. Nomenclature: Glyphosate; 2,4-D; cotton, Gossypium hirsutum L. ‘Acala 1517-95’; sweet corn, Zea mays L. ‘Sweetie 82’. Additional index words: Crop injury, nontarget crops, off-site movement. Abbreviations: DAT, days after treatment; OM, organic matter; NMSU-PSRC, New Mexico State University Plant Sciences Research Center.

Dissipation of flurtamone in three Georgia soils.

The dissipation of flurtamone was determined in three Georgia soils in 1987 to 1989. Flurtamone dissipation in soil was initially rapid but gradually slowed throughout the sampling interval. Dissipation was not affected by rate (0.8 or 1.7 kg ai ha-1) or application method (PPI or PRE). Dissipation rates were slightly more rapid in the Greenville and Dothan soils than in the Cecil soil, with calculated initial half-lives for each respective soil being 6 to 7, 8 to 10, and 9 to 23 days. There was no effect of previous flurtamone exposure on the dissipation rate in soil at any location. Nomenclature: Flurtamone, 5-(methylamino)-2-phenyl-4-[3-(trifluoromethy1)phenyl1-3-(2H)-furanone. Additional index words. RE-40885, persistence, enhanced degradation, peanut, Arachis hypogea L., cotton, Gossypium hirsutum L., grain sorghum, Sorghum bicolor L.

Dissipation of imazaquin in southern soils

Abstract Soil‐applied imazaquin was characterized by rapid initial dissipation followed by a slower second phase breakdown following field application in soybean. Relative rates of imazaquin dissipation from fastest to slowest in 1988 were: Captina silt loam = Marietta loam > Dothan (NC) loamy sand = Dothan (FL) sandy loam = Port loam = Pullman silty clay loam = Appling sandy loam = Maury silt loam = Statler loam. No differences in dissipation rate among sites were not detected in 1989. In 1990, relative rates of imazaquin dissipation from fastest to slowest were: Port loam > Dothan (FL) loamy sand = Dothan (NC) sandy loam = Appling sandy loam = Maury silt loam = Pullman silty clay loam. A negative correlation between soil temperature and the imazaquin DT50 was observed. Soil pH, organic matter content, or clay content did not influence the dissipation pattern of imazaquin in these studies.