Aphids on Milkweed

Asked September 17, 2018, 8:04 PM EDT

I had a significant issue this summer with large masses of yellow aphids infesting a batch of common milkweed, some spilling over to a small stand of swamp milkweed and a butterfly bush. I had the start of a problem last year also. I did not use any pesticide, even the insecticidal soap products, for fear of killing monarch eggs or caterpillars. They really devastated the plants they infected, killing the flowers and plants. I just pulled out the infested milkweeds, put them carefully in lawn bags, took them to a local composting center, and recycled the lawn bags. How can I treat this (presumably) aphid infestation next year, without hurting the pollinators and butterflies. I do have a certified monarch waystation, so doing this correctly is very important to me. Please advise. Thanks so much!

Wayne County Michigan sustainable gardening and landscaping insect issues butterflies monarch butterflies

1 Response

Keeping a careful track of the monarch life stages can be a start. If you know that the monarch population is mostly in the egg, chrysalis or adult stages, an insecticidal soap application will do far less harm than it would to caterpillars.

Rather than pulling out entire plants, you could just cut off the most infested parts (usually the succulent growth). Aphids on the cut off portion will not survive for long, nor will they be able to move very far, so there is usually no need to dispose of them in any complicated manner. It will often induce new growth from other parts of the plant which will be good food resources for monarchs.