Is the mold on them because it's in a container for young instars? If so, I'd say I'd probably try to find new young leaves. If it's outside, I'd remove the infected leaves just to be in the safe side.

I'm sorry that I can't answer your question but wanted to say that I had the same problem here with my swamp milkweed. I had 100 plants and dug them all out because in the summer they'd get black spots all over the leaves, which I assume was mold. The leaves would get so ugly and I assumed unusable for the Monarch cats that I decided to just concentrate on having tropical milkweed for them.

I also have butterfly weed, which keeps dying out. The Monarchs don't like it much here to lay their eggs on anyway. Those leaves sort of get ugly too but no as much as the swamp milkweed leaves did.

I've tried purple milkweed, which didn't survive long. I opted to plant tropical milkweed here every year, which the Monarchs seem to prefer to lay their eggs on here. I also like the fact that it blooms up until frost.

I wish I knew the solution for the mold on the milkweed leaves. I just wanted to let you know that I had the same problem.

Cathy

Thanks for a reply!! I asked because at that time I had 45 Monarch caterpillar mouths to feed, and the plants were heavily mildewed as seen in the photo. I wondered if the mold was toxic for the caterpillars? I picked the stems free of moldy leaves before using them as food, but often there were so few leaves left to use! Thankfully all mouths are now fed and in their cocoons!

I didn't overhead water and the plants are in full sun. My yard seems to have chronic mold & mildew issues for the last few years. I keep all plant debris off the ground, because it gets moldy within days. I don't mulch for that reason or make compost anymore.

The house is a raised foundation, and the wall between 2 bathrooms was black-mold infested last year. That all got ripped out and was treated, but maybe I need to spray bleach under the house sub-flooring and on the dirt in the crawl space?? Does an entire property (house and land) have to be treated for mold sometimes, anyone know? I don't use fungicides anymore on plants, though I have some old ones around. I do like how well bleach wipes out mold, wonder if it can be used on dirt? Am not sure what temp. it takes to kill mold/mildew, if covering the soil with plastic would work.

My container raised eggs and new instars all died, and some as big instars, they turned black. I switched to stems in water and had no more deaths after that.
Thanks for the input!

Cathy, thanks for sharing what happened with your milkweed. I wrote the above before your reply was posted. Which milkweeds are native to your region? Swamp? I can't scroll up to see if you mentioned Common since I'm on the preview page. I grow what's native here, A. fascicularis, but possibly climate change has moved faster then the native milkweeds have adapted? Has your climate changed?

My milkweed was so bad looking almost all spring and early summer. It had red and black splotches along with white powdery mildew, some white flies, even the Asian citrus psyllid (invasive species) came over to sample it-maybe it liked the whitefly debris. I killed most milkweed bugs and aphids manually. The black mold/mildew then came along--summer through November. Also insect damage and curled leaves. There were a few small, odd looking blisters on a green leaf, rarely though. What a battle. Thanks for sharing what you went through, that was really a lot of work and dedication! Maybe if left, the native MW's would adapt? I wonder, but don't know.Taking out 100 plants! what a job! And all those other types you tried :o(

I know that as a kid, summers here were dry and hot, and now summers seem shorter and not hot like they used to be. Used to be that July 4th's were HOT evenings, but for the last 10-15 years, I usually wear a sweater watching fireworks, the young kids wanted a blanket 2 years ago! Very strange. I used to wish it would be in the mid 70's all year, but now I wish for the "old days".

I wonder if getting ahold of some A.fascicularis seeds from a milder zone within it's large native area (most of Ca.) would make any difference. That would be good to know if the native milkweed varies genetically within it's native range. Maybe invasive insect species have weakened it and it hasn't adapted. Sorry you had to go through all that trouble!

HI there,

I am not sure about the mildew/mold on the ground and whether it's wise to get rid of it.

I have been doing a lot of reading on soil biology and what actually happens in healthy soil. There could be things going on like perhaps putting some active compost tea to help put in beneficial microorganisms. Also, perennial plants, trees, shrubs prefer fungal dominated soils, which usually means a soil that is fed by whole leaves.

So, maybe what you're seeing is good, or it could be bad and needs some good organisms to keep it in check.

You could send a sample of your soil to SoilFoodWeb--they check for micorganisms.

Another idea is to move your milkweed or sow some new milkweed elsewhere.

If I were going to sterilze the soil, I think solarizing would be the way to go. Put down a tarp or something and leave it for a time; I'm sure there are some directions online somewhere.

The books that I've read are Teaming with Microbes and another is Life in the Soil. It is really amazing and something all gardeners and yard owners should read.

Thanks for the ideas and book recommendations, I emailed your post to myself because maybe it's not possible to print posts. I think I might have my soil analyzed. The books sound great. It could be that the soil needs some beneficial microorganisms. Most of the leaves have fungus so I don't feel safe making tea or compost, but I'll be on the lookout for some good compost elsewhere to make tea with. The nursery offers some microbe rich supplements I noticed.

The last 2-3 years, my red grapes have fungus and aren't edible and the crepe myrtle gets powdery mildew and hasn't bloomed. The fig tree gets fungus at the end of the season. I took out a Ca. black oak tree because it looked like it had been flocked with fake snow but it was powdery mildew.

I'm considering re-landscaping to desert style. There are plants that I will keep, and will try the native flower garden next spring. No more lawns, the cost of water is out of sight.

Thanks for so much useful information.