Milkweed leaves spotting
Hi, my white swamp milkweed has brown spots on lower leaves. The leaves then turn yellow and sometimes fall off but hang by an invisible thread. There is a pink milk weed next to it is doing fine. That plant has three monarch caterpillars in their 4th or 5th instar and three milkweed bugs and a few bug babies.
The black spots on the leaves may be due to some minor leaf spots and there may be some insect feeding. It is late in the season and the plant can tolerate this type of damage. No control is necessary. Monitor the growth of the plant next season and send us photos if you notice additional symptoms.
We recommend that you leave the foliage on the plants and let any caterpillars finish development. It is not worth spraying.