Oleander aphid prevention

Asked September 29, 2020, 3:58 PM EDT

My milkweed was covered with these pests this summer. Next year what can I do to prevent the bug from laying eggs? Will winter cold kill the aphids or do they burrow in the ground waiting for summer. I had so many beautiful monarch caterpillars on the milkweed and very few leaves for them to eat. I read the article you have on killing the aphids. I am most interested on preventing them. Any suggestions you can give will be appreciated. Shirley Eatmon

Carroll County Maryland

1 Response

Hello Shirley,

Oleander Aphids are a very common pest on Milkweeds, mainly because they are one of the few insects that can consume Milkweed with no toxic effects. Predatory and parasitic insects often knock-down aphid numbers quite well on their own, but some years (like this year), there are unknown reasons why these beneficials don't do as good of a job. With this particular pest, their chemical defenses (derived from the Milkweed sap) may play a role in defending them from predation.

Any pesticide sprays - even organic ones - could impact beneficial insects, pollinators, and of course Monarch butterfly eggs, larvae, and chrysalids. As such, their use should be a last resort. If any aphid controls are needed, you can blast them off with a strong spray of hose water or squish them with your gloved fingers before trying horticultural oil.
https://extension.umd.edu/hgic/topics/orange-aphids-milkweed (this might be the article you already saw)


Prevention would only be achievable with a systemic insecticide, which would poison the aphids as they first begin to feed and colonize the plant. Their use would not be recommended at all, since the plant would then become unusable to most or all other Milkweed-dependent insects; such insecticides are non-selective in what insects they affect. Similarly, a physical barrier like a crop-protection insect-excluding fabric will also prevent the use of the Milkweed by butterflies and other harmless visitors.

We find mixed or uncertain reports on how these particular aphids spend the winter; some references say they can overwinter (either as juveniles or adults, it's unclear; they do not seem to lay eggs at any point in their life cycle) and others think they re-colonize northern areas each year from locations further south where they can survive winter temperatures. (Aphids can easily ride air currents like many other tiny arthropods, so being wind-swept into far-flung territories to repopulate them each year is a plausible means of dispersal; other insects pests in our area are known to do this.) It's possible our warming climate is making outbreaks worse or more common if it allows Oleander Aphids to survive locally in mild winters.