Milkweed pests and problems

Almost nothing you find on a milkweed needs killing. The bright orange aphids are the exception people ask about most, and even they rarely matter.

You planted this to feed insects. A milkweed covered in insects is a milkweed doing its job, and almost everything you find on one can be left alone.

Do not spray anything. Insecticidal soap, neem, pyrethrin and horticultural oil all kill monarch eggs and young caterpillars. So does a systemic neonicotinoid, for months afterward. No spray removes aphids and spares monarchs.

Oleander aphids

The bright yellow-orange aphids that coat milkweed stems are Aphis nerii, the oleander aphid. They are non-native, they reproduce asexually, and every one you see is female. They are the single most common milkweed question there is.

Do they harm the plant? Rarely much. Heavy infestations can distort new growth, reduce flowering and coat leaves in sticky honeydew that grows sooty mold. Established plants shrug it off. Seedlings and containerised plants suffer more.

What to do, in order of preference:

1. Nothing. Ladybird larvae, lacewing larvae, hoverfly larvae, parasitic wasps and soldier beetles all arrive within a couple of weeks and eat the colony. If you spray, you kill the predators too, and the aphids, which reproduce faster, come back stronger.
2. A jet of water. Knock them off with a hose. They rarely climb back up. Repeat every few days if you like.
3. Squash them by hand. Run gloved fingers up the stem. Check carefully for monarch eggs first. They are pale, ribbed and the size of a pinhead, usually on the underside of a leaf.
4. Cut off the worst tip growth, if a single shoot is smothered and has no eggs on it.

Milkweed bugs

Large milkweed bugs (Oncopeltus fasciatus) and small milkweed bugs (Lygaeus kalmii) are orange and black seed feeders. They cluster on pods, pierce seeds and drink the contents.

They do no harm to the plant. If you are collecting seed they are a genuine nuisance, in which case bag the pods early or pick the bugs off. Otherwise leave them: they are native, they are part of the community, and their aposematic coloring is one of the classic examples of Müllerian mimicry in North America.

Milkweed tussock moth

Fuzzy caterpillars in tufts of black, orange and white, feeding in a group, usually appearing in late summer. Euchaetes egle is native and eats milkweed for the same reason monarchs do.

A tussock moth colony can strip a plant completely, which alarms people. By the time they appear, from August onward, the plant has usually finished supporting monarchs for the year, and it will return unharmed next spring. If you genuinely need the foliage for late monarch caterpillars, move the tussock moths to another plant rather than killing them.

Beetles

• Red milkweed beetle (Tetraopes tetrophthalmus): red with black spots and very long antennae. Larvae feed on roots, adults on leaves. Harmless at garden scale, and the specific name is a joke about its split eyes, through which the antennae pass.
• Swamp milkweed leaf beetle (Labidomera clivicollis): rounded, orange and black, like a large ladybird. Chews leaves. Harmless.
• Japanese beetle: non-native and worth removing by hand into soapy water if numbers are high.

Real problems

Only a few things genuinely damage milkweed.

Crown and root rot. The commonest killer of garden milkweed, and always a drainage problem. Butterfly weed in clay that stays wet over winter will die. Plant dry-country species on a slope, in a raised bed, or in gritty soil, and stop watering established plants.

Damping off in seedlings. Overwatered, poorly ventilated seed trays. Use fresh compost, water from below, give the seedlings air movement.

Aster yellows. A phytoplasma disease causing distorted, greenish, stunted flowers. Uncommon and incurable. Remove and destroy affected plants.

Deer and rabbits. Mostly avoid milkweed because of the latex, but young shoots are sometimes browsed in spring. Damage is usually cosmetic.

The neonicotinoid problem

The most serious threat to a garden milkweed is not an insect. Neonicotinoid insecticides are systemic: applied to soil or seed, they move into every part of the plant, including leaves, pollen and nectar, and persist for months to years. Milkweed grown with neonics kills the caterpillars that eat it.

Nursery stock is often treated. Ask the question directly, "have these been treated with neonicotinoids?", and if nobody can tell you, buy elsewhere. Native plant nurseries and native plant society sales are the safest sources, and seed you grow yourself is safest of all.

Frequently asked questions

References

1. Agrawal, A. A. (2017). Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. The standard general account of the milkweed and monarch relationship. View
2. Borders, B. and Lee-Mäder, E. (2014). Milkweeds: A Conservation Practitioner’s Guide. The Xerces Society for Invertebrate Conservation, Portland, Oregon. Seed production, establishment and habitat management at field scale. View

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BibTeX @misc{milkweedusa_guidesmilkweedpests, title = {Milkweed pests and problems}, author = {{Milkweed USA}}, year = {2026}, url = {https://milkweedusa.com/guides/milkweed-pests/}, note = {Accessed DATE} } Copy