UNL CropWatch May 5, 2011 Spray Early with Roundup Ready Alfalfa
May 5, 2011
If you planted Roundup Ready® alfalfa this spring, it may be time for that first herbicide application. Early seedling management of Roundup Ready alfalfa is somewhat different than with regular alfalfa.
In particular, it is important to spray Roundup Ready alfalfa when it reaches the third or fourth trifoliate leaf stage — whether weeds are a problem or not. Eliminating competition will help establish thicker, more productive stands more rapidly.
If weeds aren’t a problem at this stage, why spray? Because alfalfa varieties are different from Roundup Ready corn and soybeans. Not all seedlings of Roundup Ready alfalfa will be resistant to Roundup. For most varieties, about 5% of seedlings will be susceptible to the herbicide. To avoid problems with these plants dying after Roundup application, eliminate them while all plants are still very young.
During the seeding year, alfalfa stands naturally thin as more vigorous plants out-compete smaller plants. The surviving plants fill the gaps and become even more productive as competition is reduced. By removing Roundup-susceptible plants as young seedlings, the gaps they leave will be filled easily by remaining Roundup-resistant plants. If you wait until the stand is well established before making your first Roundup application, gaps left as susceptible plants die may not be filled as easily.
To make sure your alfalfa stand remains thick and productive, spray Roundup early to eliminate all susceptible plants.
Extension Forage Specialist