Glyphosate-resistant alfalfa offers new weed control options for alfalfa establishment. Field studies were conducted in 2004 and 2005 to determine the effect of establishment method and weed control method on forage production and alfalfa stand establishment. Seeding methods included clear seeding and companion seeding with oats. Herbicide treatments included glyphosate, imazamox, imazamox clethodim, and no herbicide. Temporary stunting from the glyphosate treatments was observed (< 7%); however, injury did not reduce forage yield or stand density in 2004. No glyphosate injury was observed in 2005. Weed control with glyphosate was more consistent than with imazamox or imazamox clethodim. In 2004, total seasonal forage yield, which consisted of alfalfa, weeds, and oats (in some treatments), was the highest where no herbicide was applied in the oat companion crop and was reduced where herbicides were applied in both establishment systems. In 2005, seeding method or weed control method did not affect total seasonal forage production. Alfalfa established with the clear-seeded method and treated with glyphosate yielded the highest alfalfa dry matter in both years. Imazamox injury reduced first-harvest alfalfa yield in the clear-seeded system in both years. When no herbicide was applied, alfalfa yield was higher in the clear-seeded system. The oat companion crop suppressed alfalfa yield significantly in both years. Alfalfa established with an oat companion crop had a lower weed biomass than the clear-seeded system where no herbicide was applied in both years.

Nomenclature: Clethodim, glyphosate, imazamox, alfalfa, Medicago sativa L., oat, Avena sativa L. ‘Ida’