The Q&A Archives: Brown Spots On Rudbeckia

Question: My Black-eyed Susans have brown spots on their leaves with curled edges and white sticky "foam" on the stems. What is it and how so I treat it?

Answer: You may be dealing with two problems on your Black-Eyed Susans. The sticky foam is likely the protective coating of the spittle bug. These are tiny sucking insects that produce a bubbly liquid to help hide them from predators. Unless the infestation is exceptional, I'd just spray the foam off with water from the hose. That will make the spittle bug spend more of its time making foam, and less time sucking fluids from the tissues of your plants. The brown spots and curling leaves indicate a cultural problem. Either your plants are diseased, or they're over or under watered. Make sure your plants are in full sunshine, have good air circulation, and you're applying water to the soil only after it has dried out. Pick off the leaves in question and remove them from the garden to keep any possible disease pathogens from spreading to other plant parts.

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