When average numbers exceed 20-30 aphids per crown, application of insecticide should be considered in order to prevent death of plants. Weekly sampling in new stands of alfalfa should be conducted to detect spotted aphid infestions and prevent serious damage. Newly established alfalfa plants have much less tolerance for aphid infestations than older plants. Insecticide applications should be made in new stands if numbers of aphids exceed 3 per plant. Heavy infestations and damage to alfalfa has been found in Grady County as recently as December 1.
Check fields weekly.
To sample short, crown growth in established stands, place a light-colored card on the soil surface below crowns, and brush the foliage to dislodge aphids. If average numbers exceed 20-30 aphids per crown, application of insecticide should be considered. In new stands planted this fall, insecticides should be applied if numbers of aphids exceed 3 per plant. We are frequently asked what we think about working old alfalfa fields. With this different terminology from alfalfa producer to producer, sometimes in the same county, the question becomes difficult to answer.