Disease? on my milkweed plants last summer

Asked March 30, 2018, 1:16 PM EDT

I am sorry that I do not have a photo. For the past four years or so, I have grown milkweed in my backyard. Two summers ago, I actually saw two monarch caterpillars on my plants, which was super exciting. Last summer (2017) I was hoping to see caterpillars again, but never did. What did happen, though, is that many of the leaves seemed to get covered in a dark brown substance that seemed a bit sticky, and rather than attracting caterpillars, there instead seemed to be a bunch of wasps that liked to hang out on the leaves (not together). It started off with only a few leaves having this appearance but by the end of the summer, pretty much all of my milkweed plants looked like that. I wasn't sure if I should remove the leaves or not, and I ended up doing nothing. This time, I would like to get ahead of the game and know what to look out for. Is there any way, based on what I described, for someone to tell me what was the source of the disease or infestation on my milkweed plants, and how I might be able to prevent it or treat it if it happens again this year? Thank you,

Montgomery County Maryland

1 Response

Based on your description it is possible that you may be referring to possible insects on your milkweeds, such as the oleandar aphid and/or the milkweed bug.
The aphids are sucking insects that suck sap and exude a honeydew that fosters the growth of a black sooty mold. Wasps can be attracted to the honeydew.

Milkweed bugs are more of a nuisance than a threat to milkweed plants. The milkweed bugs and the plants have coevolved together and usually the plant can tolerate the damage. Otherwise sweep the bugs into a container of soapy water.

Take a look at our website and the Missouri Botanical Garden for more information and what to look for http://extension.umd.edu/hgic/earth-friendly/aphids-got-your-milkweeds

This season monitor your plants for signs of possible insects and symptoms. You can send us some photos this growing season once you notice symptoms.