Black fungus and Tiny black dots on milkweed - Ask Extension
My milkweed in past seasons develop sooty black leaves in July or august. The chrysalis have been turning black and contain liquid. Last year I pulled...
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Black fungus and Tiny black dots on milkweed #870919
Asked May 31, 2024, 10:58 AM EDT
My milkweed in past seasons develop sooty black leaves in July or august. The chrysalis have been turning black and contain liquid. Last year I pulled up all the milkweed so it wouldn’t kill the monarchs. This year, I was hoping to get on top of it. What are these little tiny black dots? They’re so neatly organized around the base of the leave stem and also in the crevice where the leaf stem attaches to the plant. I also included photos of other issues that I was curious about. Curling leaves, yellow scaly row…. I read that watered down hydrogen peroxide sprayed on and under the leaves could help prevent the black soot/fungus. Will it harm the monarch’s if I do that? I don’t see any monarchs yet.
Baltimore City County Maryland
Expert Response
We don't have an ID for the tiny black clusters of dots on the leaf base, but it's not likely something harmful, and it is not sooty mold. Hydrogen peroxide is not intended to be used on plants unless it comes in a package labeled specifically as a pesticide. Its use would not only potentially harm any organism the spray contacts, but it might "burn" the foliage as well. Sooty mold wears-off on its own over time and it does not infect plants, nor (to our knowledge) kill caterpillars.
The other photos is hard to see clearly, but it appears to be the dried sap residue of the Milkweed plant itself. Chewing insects that feed on Milkweed usually chew into the main leaf vein to cause it to ooze sap before they start consuming the leaf tip. This reduces the amount of gummy sap they are exposed to, protecting their mouths and digestive system. It's natural behavior and won't cause serious harm to the plant, which will outgrow the damage. No intervention is needed.
A Monarch chrysalis that dies or fails to hatch properly could have been affected by a range of natural factors. Insects can get sick from insect-specific viruses, fungi, bacteria, and parasites. Other insects (parasitoids) can also kill them from within, and predatory insects can feed on the defenseless chrysalis as well, killing the developing adult inside in the process. These are all natural events and there is no way to prevent them. Pulling up the Milkweed shouldn't be necessary, so if it happens in the future, it's not harmful to keep the Milkweed around for the benefit of other insects and pollinators visiting its flowers.
Miri
The other photos is hard to see clearly, but it appears to be the dried sap residue of the Milkweed plant itself. Chewing insects that feed on Milkweed usually chew into the main leaf vein to cause it to ooze sap before they start consuming the leaf tip. This reduces the amount of gummy sap they are exposed to, protecting their mouths and digestive system. It's natural behavior and won't cause serious harm to the plant, which will outgrow the damage. No intervention is needed.
A Monarch chrysalis that dies or fails to hatch properly could have been affected by a range of natural factors. Insects can get sick from insect-specific viruses, fungi, bacteria, and parasites. Other insects (parasitoids) can also kill them from within, and predatory insects can feed on the defenseless chrysalis as well, killing the developing adult inside in the process. These are all natural events and there is no way to prevent them. Pulling up the Milkweed shouldn't be necessary, so if it happens in the future, it's not harmful to keep the Milkweed around for the benefit of other insects and pollinators visiting its flowers.
Miri
