Timing of Glyphosate Application for Weed Control in Glyphosate Tolerant Lettuce

Abstract

Studies were conducted to determine the optimum time to apply glyphosate to glyphosate-tolerant Lactuca sativa cv. Raider (head lettuce). The study was initiated near Yuma, Arizona in September 2000. Single applications of glyphosate at 1.0 lb AI/A were made to head lettuce at development stages of 2, 4, 6 and 8 leaves. Glyphosate treatments did not injure lettuce. A single application at the 2 or 4 leaf stage was optimal for near complete control of Portulaca oleracea (common purslane), Chenopodium murale (nettleleaf goosefoot), Malva parviflora (cheeseweed), and Leptochloa spp. (sprangletop). Later applications at the 6 or 8 leaf stages allowed weeds, especially, common purslane to compete with the crop. Treatments applied at the 2 or 4 leaf stages required the least amount of time to hand weed and resulted in highest fresh weight yields.