The antennae provide the distinguishing characteristic. A black fungus that grows on the honeydew excreted by the aphid reduces palatability. When selecting varieties, consult your farm advisor for information on varieties suited to your area. When parasites are present, be careful when treating for aphids and other insects.
Parasites frequently provide adequate control.
This will dislodge the aphids and they can be easily counted. This procedure should be repeated, cutting a number of stems at several locations in the field. In southern California, a blue alfalfa aphid population of 10 to 12 per stem on new regrowth during the January, February, and March cutting cycles will later reduce yields because natural enemies are not present to suppress populations. If alfalfa is cut when aphid populations are in this range, monitor regrowth carefully. Treat if populations exceed this level.