Scouting time
Egg hatching occurs in the early spring, and the young nymphs feed on new growth of alfalfa or clover. They molt four times before becoming adults.The blue alfalfa aphid prefers to feed on the tender succulent parts of the alfalfa plant. These aphids cluster on the terminal growth, but as populations increase, they will spread over the entire plant. Heavily infested alfalfa is characterized by severe stunting of the stems, which have shortened internodes and smaller leaves. Leaf curling and eventual leaf drop are also common symptoms in severely infested fields. Large blue alfalfa aphid populations have delayed cutting schedules or have caused the loss of a full cutting. Usually, only a patch of the field is affected.
Sampling method
Randomly select complete stems throughout the field, count the number of blue alfalfa aphids per stem, plus all parasitized (mummified) or diseased (brown and flattened) aphids. Continue this procedure until you have sampled at least 20 to 30 stems. Calculate the average number of healthy aphids per stem and the average of diseased or parasitized aphids per stem. Then measure each stem and calculate the average stem length.
Thresholds
Stunting of plant growth is evident at lower infestation densities than with pea aphid feeding. For instance, 20 blue alfalfa aphids per stem on 10-inch-tall alfalfa, or 50 blue alfalfa aphids on 20-inch-tall alfalfa, may justify insecticide treatment. if diseased and parasitized aphids are scarce.
Chemical control
|
Insecticide |
Rate |
|
Alpha-cypermethrin (Fastac EC) |
0.014 to 0.025 lb. a.i./acre (2.2 to 3.8 fl. oz./acre) |
|
Beta-cyfluthrin (Baythroid XL) |
0.022 lb. a.i./acre (2.8 fl. oz./acre) |
|
Chlorpyrifos (numerous products) |
Check label, but generally 1 to 2 pints/acre |
|
Chlorpyrifos plus gamma-cyhalothrin (Cobalt) |
13 to 26 fl. oz. of product/acre |
|
Chlorpyrifos plus zeta-cypermethrin (Stallion) |
9.25 to 11.75 fl. oz./acre |
|
Dimethoate (Dimethoate or Dimate) |
0.25 to 0.5 lb. a.i./acre |
|
Gamma-cyhalothrin (Proaxis) |
0.01 to 0.015 lb. a.i./acre (2.56 to 3.84 fl. oz.) |
|
Lambda-cyhalothrin (numerous products) |
0.02 to 0.03 lb. a.i./acre |
|
Lambda-cyhalothrin plus chlorantraniliprole (Besiege) |
6.0 to 10.0 fl. oz./acre |
|
Permethrin (multiple products) |
0.05 to 0.2 lb. a.i./acre |
|
Zeta-cypermethrin (Mustang MAXX, etc.) |
0.014 to 0.025 lb. a.i./acre (2.24 to 4.0 fl. oz.) |
Non-chemical controls
None listed.
Content authors
Disclaimers
This content may not be suitable for states other than Kansas.
