Biological control is much more effective in the eastern United States, perhaps because of climatic differences. Commercially available biological control agents are not known to be effective against alfalfa weevil. For more information, see fact sheet 5.500, Alfalfa Weevil . Pea Aphid Pea aphid and, much less frequently, spotted alfalfa aphid or blue alfalfa aphid may damage stands by stunting and wilting plants. Pea aphid outbreaks are most common following insecticide applications.
Aphid damage is generally rare, due to effective biological control and resistant cultivars.
Aphid-resistant alfalfas help avoid outbreaks associated with chemical control of alfalfa weevil. Consider chemical control if there are more than 10 aphids per stem two weeks before cutting. For more information, see 5.531, Aphids in Alfalfa . Blister Beetles Adult blister beetles are strongly attracted to alfalfa and other blooming hosts. Damage is not important, but the presence of blister beetles, especially the large, striped swarming types, is a concern for producers who sell hay to horse owners.