Answer: I wonder if the black dust is sooty mold? If you can scrape it off with your fingernail or wipe it off with a dampened paper towel, it's probably sooty mold. If so, look for insects feeding on the leaves or stems just above the sooty mold. When they feed they excrete a sticky substance called honeydew which eventually turns black. Insecticidal soap will control aphids, whiteflies, mealybugs and other sucking insects. Good luck with your garden!
Q&A Library Searching Tips