EFFECTS OF SOIL TEMPERATURE ON THE PHYTOTOXICITY OF TRIFLURALIN TO WILD OATS

Experiments were conducted in the field and in controlled environment chambers at Beaverlodge, Alberta to determine the influence of soil temperature on the phytotoxicity of trifluralin (α,α,α-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine) to wild oats (Avena fatua L.). In the field trifluralin reduced wild oat emergence the most in early May when soil temperatures were lowest. As soil temperatures increased in May, the effectiveness of trifluralin in reducing wild oat emergence declined. In controlled environment studies, the effectiveness of trifluralin in reducing wild oat shoot growth was greatest at 4 °C. At 7.5 °C, the effectiveness of trifluralin in reducing wild oat shoot growth declined. However, at both 10 and 20 °C, small increases in trifluralin phytotoxicity occurred. Exposure of wild oat shoots to trifluralin vapors at 7.5 and 20 °C indicated decreased shoot growth of wild oats at 7.5 °C but increased volatilization of trifluralin at 20 °C. Thus, the lack of any major differences in the effectiveness of trifluralin in reducing wild oat shoot growth at temperatures from 7.5 to 20 °C may be due to the counteraction of these two phenomena.