Quackgrass control with glyphosate and SC-0224 in corn and soybean

Abstract

Studies on quackgrass control were conducted using a factorial combination of glyphosate or SC-0224, each at 0.28, 0.56 and 0.84 kg ha−1, and ammonium sulphate at 0 and 2.5 kg ha−1 in corn and soybean plots on a severe infestation in southwestern Ontario during 5 yr. The two herbicides at a given rate provided similar degrees of quackgrass control. With the addition of ammonium sulphate, the effective rate of both herbicides was reduced from the recommended rate of 0.9 kg ha−1 to 0.56 kg ha−1, which results in a higher economic return. Although a lower rate, 0.28 kg ha−1, also provided satisfactory initial control of quackgrass, there was a tendency to increasing quackgrass coverage with time despite the repeated application of herbicides over years. After 5 yr of treatment at a consistently low rate (0.28 kg ha−1), quackgrass coverage approached the original level in the soybean field. The increase in quackgrass coverage caused a corresponding reduction in soybean yield. The results suggest that glyphosate or SC-0224 at about 0.56 kg ha−1 is effective when applied in conjunction with ammonium sulphate. Lower rates may be acceptable if used with a high rate at properly chosen intervals. Key words: Quackgrass control, glyphosate, SC-0224, ammonium sulphate, soybean, corn