Effect of Growth Stage and Environment on Foliar Absorption, Translocation, Metabolism, and Activity of Nicosulfuron in Quackgrass (Elytrigia repens)

Abstract

Experiments were conducted to examine the influence of adjuvant, growth stage, air temperature, and soil moisture on nicosulfuron activity, absorption, and distribution in quackgrass. Foliar absorption of14C-nicosulfuron by quackgrass was greater in one-leaf than five-leaf plants. Total translocation of14C-nicosulfuron was similar regardless of growth stage. However, nicosulfuron was more phytotoxic to three- and five-leaf than one-leaf quackgrass. Of the absorbed14C, at least 71 % remained as14C-nicosulfuron 168 h after application in three-leaf plants.14C-Nicosulfuron absorption, translocation, and accumulation increased with increasing temperatures and was independent of soil moisture. Under adequate soil moisture conditions (-0.03 MPa), nicosulfuron activity was not influenced by temperature. Nicosulfuron efficacy was not influenced by soil moisture at a cool (11/6 C) temperature. As plant moisture stress increased, due to low soil moisture and increasing air temperature, nicosulfuron efficacy declined. Differences in nicosulfuron efficacy due to growth stage or environmental conditions could not be explained by differential14C recovery, absorption, translocation, or accumulation. The addition of 28% urea-ammonium nitrate liquid fertilizer (UAN) to14C-nico-sulfuron plus petroleum oil adjuvant (POA) provided greater14C absorption than POA alone. Translocation of14C with POA alone 168 h after treatment (HAT) was similar to POA plus UAN 24 HAT. However, 168 HAT there was no difference in the total amount of radiolabelled material translocated among the adjuvants.