Delayed Glyphosate Application Doesn’t ReducePlant Density of Glyphosate-Tolerant Alfalfa

摘要

Commercial seed of glyphosate-tolerant alfalfa contains small percentages ofseeds, called nulls, that do not posses the herbicide trait. Differentialcompetitiveness of glyphosate-tolerant seedlings compared with null seedlingsmay be detrimental to alfalfa stand density if delayed glyphosate applicationallows the null and tolerant seedlings to compete with each other. Our objectivewas to determine if delayed glyphosate application affects plant density ofglyphosate-tolerant alfalfa stands. Commercially available glyphosate-tolerantalfalfa was seeded at 17 and 29 kg/ha, plots were treated with glyphosate onemonth (3- to 6-trifoliate leaf stage) or one-year after planting and plant densitywas monitored throughout the study. Regardless of seedling rate an average of6.5 and 5.5% of the alfalfa plants died when glyphosate was applied one monthand one year after planting, respectively, but plant density remained unchangedduring the same time periods when glyphosate was not applied. Planting alfalfa at17 kg/ha resulted in lower seedling density, but also lower plant mortality duringthe seeding year than planting at 29 kg/ha. We conclude that delaying glyphosateapplication to glyphosate-tolerant alfalfa until one year after planting does notalter the percent of glyphosate-tolerant and non-tolerant plants.