Bruce Anderson, UNL Extension Forage Specialist reminds producers that with late first cuttings of alfalfa, alfalfa weevil activity often increases when this occurs. Anderson says that weevil larvae generally eat small holes in leaves at the growing tip of alfalfa plants. As larvae grow, damage increases as the holes become larger. Severely damaged fields have a grayish appearance because of the drying of skeletonized upper leaves and buds.
Most fields have not had enough damage to need spraying before first cutting. After harvest, many larvae die when exposed to direct sunlight and high temperatures at the soil surface. But will enough larvae survive to be a problem for regrowth?
Maybe more likely is survival of weevil adults. These critters can be really hard on alfalfa regrowth by feeding on the developing crown buds, retarding growth and preventing fields from greening up after harvest.
Your first step in controlling weevil adults is removal of windrows and bales as soon as possible to expose these insects. Then examine stubble frequently to see if adults are delaying greenup by feeding on new buds, especially where the windrow laid.
If damage is noticed, a threshold guideline has been developed that uses insecticide cost, hay value, and harvest management to help you determine when spraying may be desirable. This guide, along with other tips to manage alfalfa weevil, is available from local extension offices.
Don’t let alfalfa weevil adults delay second growth of your alfalfa. Keep a watchful eye on the stubble and spray, but only if necessary. Download our UNL Extension NebGuide for more information.