Influence of Temperature and Adjuvants on Thidiazuron Activity in Cotton Leaves

Abstract

A laboratory study was conducted to determine the effects of two adjuvants and temperatures at time of treatment on efficacy, absorption, and translocation of thidiazuron defoliant on cotton. Five days after treatment at 30/21 C day/night temperatures, leaf drop was 17% with no adjuvant, 37% with addition of crop oil concentrate, 40% with ammonium sulfate, and 75% with two adjuvants combined. At 21/13 C day/night temperatures, there was less than 10% leaf drop with all treatments. At 10 d after treatment, leaf drop was not different among treatments at the high or low temperatures. Shoot regrowth at high and low temperature was reduced 55 to 60% with addition of both adjuvants and 44 to 50% with each adjuvant or with no adjuvant when compared to plants defoliated by hand. Absorption of14C-thidiazuron was not affected by variations in temperature during the time of treatment but was affected by adjuvants. With no adjuvants, absorption was 7 to 10%. With 1.25% by vol crop oil concentrate, absorption was 33 to 46%. Addition of ammonium sulfate resulted in 18 to 19% absorption, and the combination of ammonium sulfate and crop oil concentrate increased absorption to 65 to 68%. There was no movement of radiolabel away from treated leaves as determined by autoradiographs of treated plants.