Aphids: What to Do? - Wild Ones West Cook Chapter

A line of lacewing eggs next to aphids. Lacewing larvae love aphids.

This post was written to address a question about aphids on milkweed. Any of the steps would apply to aphids on any other type of plant, including edibles. (Note the image at the top of the page is of a Lacewing adult, one of the beneficials that you want to attract and keep in your garden.)

Do Nothing

The best thing to do is to do nothing–if you can stand it. Eventually, beneficial insects will find the aphids and begin to control if not completely decimate the aphid population. Often we are told to squish (this writer has done that) or to blast them with a hose (also done that).

The best time to squish or hose off would be right at first sign of aphids and keep it up before predators find them. If you have a large aphid infestation and use the hose/squish methods, the aphids will certainly be gone, but you might also be washing away their predators.

Once you can identify the beneficial insects and know that they are not present, you can wash away aphids away in confidence, knowing that you are not harming Monarch or beneficial insects. It’s equally important to learn about these natural predators and how to support all stages of their life cycles so that they can keep aphids in check as soon as they arrive. Be sure to check for caterpillars and eggs first though too. Hatchling caterpillars are very tiny and fragile.

No Need to Shop for Beneficial Insects

No need to order or buy adult ladybugs (they usually fly away and may negatively impact native ladybug populations). It’s better to wait for reinforcements, which will be sooner if you didn’t do extensive garden clean-up in the fall/spring and a little later if you did do a lot of clean-up because they will have to migrate in from elsewhere. Arriving in short order will be other allies too–Soldier Beetles, Ladybugs, Lacewing larvae, parasitoid wasps, predatorial wasps, Minute Pirate Bugs, Whirlygig Mites, Long-legged Flies, Earwigs (!–yes they are aphid predators) and Syrphid Fly larvae. All of these and other predators will dine on the aphids too. (Pictures of some of these found below.)

Have Milkweed Back-up

It’s a good strategy to have several plants of milkweed in different areas of the garden (as well as different species) because if one plant gets aphids, chances are the other plants will ramp up their defenses (and the Monarch caterpillars will appreciate the abundant milkweed) Here is an article by Michael Pollen that discusses this defense alert system, among the many other wonders of plants: The Intelligent Plant or this article: How Plants Talk to Each Other). I have noticed in my own garden that one milkweed will get aphids, and there might be a few on the other, but it stays quite limited. But usually by that time, the predators have found the aphids, so it’s hard to know if the nearby plants have picked up on the “victim” plant’s signals, or whether the predators have things under control, or if it’s a combination of the two.

It’s All About Community

Plant a lot of native plants to support lots of insects that eat plants, and the predators will be around consistently, including parasitic wasps. f you have many native plants, trees, bushes that support a lot of herbivorous insects, you will keep the wasps busy and perhaps reduce pressure off of the butterfly caterpillars. So, for instance if you only grow milkweed and some zinnias and non-native perennials, which don’t support any other caterpillar, the wasps and yellow jackets have no other option but to go after the Monarch caterpillars, and you can’t keep the wasps out of your yard.

Polished Ladybug, one of our native Ladybugs, eats an aphid

Importance of Garden Clean-up

An important but overlooked piece of information is that many of our beneficials like ladybugs, lacewings, syrphid flies, soldier beetles, etc., are year round inhabitants in our gardens. They overwinter in the garden. After planting native plants, another important strategy is to change our fall and spring clean-up practices.

The typical cut down and rake/blow everything out of the garden destroys the overwintering insects which means no predators in the immediate area next year. It’s best to have them already in your garden by keeping the garden standing and using gentle clean-up in the spring (which for me usually means clipping stalks and leaving them in the garden near the plant and keeping plant material in the garden in case any tiny beneficials are there. In some spots, I don’t clip stems at all or they get trimmed to provide nesting spots for tiny carpenter bees. ) Of course, many other wonderful butterflies/moths spend the winters here in some form. Check out the resources from Xerces Society about attracting beneficial insects; there’s a great video online too, and the presenter mentions that it takes longer for predators to return to a garden than it does for the pest insect. The predator-prey interactions are interesting, which can also lead to a deeper appreciation of these other animals. Farming for Beneficial Insects

Some of the insects that prey upon aphids might also prey upon small Monarch instars. If you find young caterpillars, you can simply move them to another milkweed plant that is aphid-free.