INFO-BUG

Crop Selected: Alfalfa
Crop Development: Third or fourth cutting

Pests Selected:

Pea aphid Acyrthosiphon pisum
Spotted alfalfa aphid Therioaphis maculata

Biology

Aphids can usually be found when sampling most alfalfa stands. However, beneficial predators and parasites generally maintain aphid populations at insignificant levels of activity.

When a significant infestation of aphids does occur, the problem can generally be related to a pesticide use strategy used which has had a detrimental effect on the beneficial populations.

Regular use of the pesticide Sevin occasionally leads to build up of aphid populations.

Assessment

While sweep net sampling 2nd, 3rd or 4th cuttings for potato leafhopper, aphid numbers should be noted.

Rating of aphid activity includes the following:

Less than 1/2 cup of aphids per 10 sweeps = Few.
From 1/2 to 1 cup of aphids per 10 sweeps = Common.
More than 1 cup of aphids per 10 sweeps = Abundant.

If aphids are abundant, rescue treatment may be warranted.

Note: it is important not to confuse identification of aphids with potato leafhoppers since levels representing economic activity of the 2 pests are significantly different.

Control

Materials recommended for control of aphids include:

Ambush*
Baytrhoid* 2
Dimethoate
Furadan* 4F
Lannate*
Lorsban* 4E
Malathion
Mustang
Pounce* 3.2EC
Warrior* 1CS

* Use is restricted to certified applicators

Early harvest of alfalfa to control aphids is preferred to use of chemical rescue treatment.

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