Environmental effects on CGA-248757 and flumiclorac efficacy/soybean tolerance

The effect temperature, light intensity, time to initial light exposure, relative humidity, and the presence of dew have on CGA-248757 and flumiclorac efficacy was evaluated in laboratory trials. Increasing temperature from 10 to 40 C increased CGA-248757 and flumiclorac activity on common lambsquarters by 79 and 87%%, respectively. Similarly, increasing temperature from 10 to 40 C increased CGA-248757 and flumiclorac activity on redroot pigweed by 68 and 60%%, respectively. Increasing light intensity from 0 to 1,000 μμmol m⁻⁻² s⁻⁻¹ increased CGA-248757 activity on common lambsquarters and redroot pigweed by 92 and 93%%, while flumiclorac activity increased 91 and 99%%. Time to initial light exposure and relative humidity did not affect CGA-248757 or flumiclorac activity on common lambsquarters and redroot pigweed. The presence of dew reduced herbicidal activity of both compounds on common lambsquarters by 5%% and redroot pigweed control with CGA-248757 and flumiclorac by 21 and 20%%, respectively. Field applications of CGA-248757 or flumiclorac at 6:00 a.m., 2:00 p.m., and 10:00 p.m. indicate environmental conditions at application strongly influence soybean tolerance and weed control with CGA-248757 and flumiclorac. The greatest soybean injury occurred from CGA-248757 or flumiclorac applications at 6:00 a.m. compared with applications at 2:00 p.m. or 10:00 p.m. Common lambsquarters control was greatest when CGA-248757 or flumiclorac was applied at 6:00 a.m. or 2:00 p.m. compared with 10:00 p.m. However, redroot pigweed control was greatest when CGA-248757 or flumiclorac was applied at 2:00 p.m. Application time of day did not affect velvetleaf control with either herbicide.Nomenclature: CGA-248757, [[[[2-chloro-4-fluoro-5-[[(tetrahydro-3-oxo-1H,3H-[[1,3,4]]thiadiazolo[[3,4-a]]pyridazin-1-ylidene)amino]]phenyl]]thio]]aceate; flumiclorac; common lambsquarters, Chenopodium album L. CHEAL; redroot pigweed, Amaranthus retroflexus L. AMARE; soybean, Glycine max (L.) Merr. ‘‘Conrad’’ GLYMA; velvetleaf, Abutilon theophrasti Medik. ABUTH.