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.)
The best thing to do is to do nothing, if you can stand it. 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. Be sure to check for Monarch eggs/caterpillars too. If you have a large aphid infestation and use the hose/squish methods, the aphids will certainly be gone, but sometimes our friends are present. We just don’t know who or where they are or have the patience to believe that they will come and save the day (or the milkweed). But if you know what the beneficial predators look like in all stages, and they aren’t on the plant, then squish or hose away. 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). 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, Lacewing larvae, parasitoid wasps, predatorial wasps, Minute Pirate Bug, and Syrphid Fly larvae. All of these and other predators will dine on the aphids too.
Have Milkweed Back-up
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. If you have a lot of 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. Guess what? 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.
It’s All About 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.
Just as a note, 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. The best thing to do though if you want to ensure the eggs/caterpillars make it to adulthood is to rear indoors. Very few of the eggs a Monarch lays will make it to adulthood when left out in the garden. Or you can just let nature take its course as well. The predator-prey interactions are interesting, which can also lead to a deeper appreciation of these other animals.