Attack on milkweed

Asked August 20, 2020, 10:40 AM EDT

Hello I have an asclepsias incarnata milkweed plant that was growing strongly until a week ago. In very short time, the leaves all wilted. I saw that there were small red balls of something (eggs I guess) as well as white ones in the pot that were smaller than grains of rice. I assume that some infestation is eating at the roots or at the stem xylem / phloem. I have a couple questions: 1) what is this? 2) how do I treat it? 3) when I see something unknown like that, would it be safe to try pouring a bit of olive oil or some other oil over the “eggs” to smoother them? Will that hurt the plant normally? 4) can the plant be saved? I had another incarnata in the ground on the opposite side of the house where the same thing happened. Last year in the same spot, I also lost two incarnata to bugs that laid eggs and then consumed them from inside the stalk. If you have any advice on that part of the garden, then also welcome because I still have a couple plants there and want to help monarchs. Thanks

District of Columbia County District of Columbia

1 Response

Hi - Unfortunately, your plant has a fungal disease called Southern blight. This disease can be a problem on many different types of herbaceous perennial plants when the weather conditions are favorable for it (hot and humid). The symptoms can come on very rapidly and, unfortunately, there is nothing you can do to alleviate the problem on afflicted plants once it occurs. At this point, sanitation is going to be the next best thing to do. The small orange seed-like structures (called sclerotia) enable the fungus to survive in the soil over winter (and up to 3-4 years). No, olive oil will not do anything to get rid of them. Remove and discard (in the trash, not compost) the affected stem and scoop out and discard the visible sclerotia. Or, even better, replace the soil altogether with fresh potting medium when you replant into the container. Here is more information about Southern blight and what you can do to manage it.

If you are noticing insects or symptoms on your other milkweed plants, feel free to send us photos and we can take a look. Milkweed bugs are a type of insect that is typically active at this time of year on milkweeds.

If milkweed growing has been challenging, you might want to explore some different plant options that would also support Monarchs. For example, asters and goldenrods are excellent nectar sources for the adult butterflies during migration in the fall.