Response of quackgrass biotypes to glyphosate and quizalofop

Abstract

The response to glyphosate and quizalofop of five quackgrass (Elytrigia repens (L.) Nevski) biotypes treated at the three- to four-leaf and six- to seven-leaf stage was tested. Shoot and rhizome-bud control 1 yr after treatment did not differ among biotypes treated at the three-to four-leaf stage regardless of the herbicides and rates. At the six- to seven-leaf stage, difference in shoot control between the most tolerant and the most sensitive biotypes was 54 and 40% after treatment with quizalofop at 100 and 150 g a.i. ha−1, respectively. Shoot control at the six- to seven-leaf stage ranged between 59 and 97%, with glyphosate at 450 g a.i. ha−1. When averaged over all treatments and stages of growth, control of shoot number was positively correlated with control of rhizome bud number. A negative correlation existed between the percent shoot control at the six- to seven-leaf stage and the number of tillers, rhizomes, and rhizome buds, and with the total biomass of the biotypes at time of treatment with quizalofop at 100 g ha−1. Leaf retention on the lower leaves of plants at the three- to four-leaf stage varied among biotypes, but was not related to treatment tolerance. Key words: Glyphosate, quizalofop, rhizome buds, shoot control, Elytrigia repens