Soybean Aphid - Insecticides

Soybean Aphid Management topics

Action Thresholds Insecticides Natural enemies and biological control

Asian lady beetles feeding on soybean aphids. Photo © University of Wisconsin

A single foliar-applied application of a labeled insecticide will effectively reduce aphid populations. The critical decision is if and when to treat.

Use an action threshold of 250 aphids per plant if populations are actively increasing. This action threshold should be based on an average of 250 aphids per plant over 20 to 30 plants sampled throughout the field. Regular field visits are required to determine if soybean aphid populations are increasing.

In replicated research trials, this threshold has worked well in late vegetative (right at first bloom) to R4 soybeans. Spraying at or beyond R6 has not been documented to increase yield.

This threshold incorporates an approximately 7-day lead-time between scouting and treatment to make spray arrangements or handle weather delays.

Timing

Timing is critical. If insecticide is applied too early, aphid populations can rebound at sensitive soybean growth stages. Applied too late and the economic benefit is lost. 

Broad-spectrum foliar insecticides kill natural enemies and may result in a resurgence of aphid populations if applied too early. This is because aphids are all female during the summer and don't need to mate. The reproduction of natural enemies is much slower and requires time for mating, egg-laying, and hatch.

Information on these pages is from the cooperative effort of researchers throughout the North Central states. Information from this site can be copied and distributed for educational use. Please credit the source with our name and URL: NCSRP Plant Health Initiative at www.planthealth.info. Please do not use copyrighted photos without permission.