Abstract
The control of quackgrass (Agropyron repens (L.) Beauv.) using glyphosate applied with either a conventional sprayer or a rope wick applicator, each followed by several levels of tillage, was studied in 1983, 1984 and 1985. With the conventional sprayer, glyphosate was either applied alone or with ammonium sulfate (3.4 kg ha−1) and the surfactant, nonylphenoxy polyethoxy ethanol (0.5% vol/vol of spray volume). Applications made with the sprayer were more effective in reducing quackgrass culm density than those made with the rope wick applicator. The density of quackgrass culms declined as the number of tillage operations increased from one, performed at 115 or more days after herbicide application (DAT), to three performed at 5–8, 39–60 and 115 or more DAT. Doubling the rate of sprayer-applied glyphosate, from 0.8 to 1.7 kg acid equivalent ha−1, did not result in a reduction in the density of quackgrass culms. However, in 1 of the 2 years in which comparisons were made, both of these treatments reduced the density of quackgrass culms more than a similar application of glyphosate alone at 0.5 kg ha−1. The addition of ammonium sulfate and surfactant to glyphosate enhanced quackgrass control only at the 0.5 kg ha−1 rate and only in 1 of 2 yr at that rate. Glyphosate, applied at 0.5 kg ha−1 with the sprayer, and followed by three tillage operations consistently reduced the density of quackgrass culms by 95% or more. Both the herbicide and the tillage treatments resulted in increases in the yield of barley seeded the following year. In 2 of the 3 years, barley yields, averaged across tillage treatments, were greater in the plots where the sprayer had been used to apply the glyphosate treatments than in the plots where the rope wick applicator had been used. Barley yields decreased as the quackgrass culm density increased, although other factors seemed to have influenced the yields in one of the years.Key words: Glyphosate, tillage, barley, quackgrass, fallow
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