I have 2 knock out rose bushes that were thriving last summer but this summer...
I have 2 knock out rose bushes that were thriving last summer but this summer its leaves have developed yellow blotches that eventually become holes until the leaves look skeletal. I am treating with an organic fungicide/insecticide and have cut away the "ill" looking leaves but it is not thriving as well. It gets watered during dry spells, gets 6-8 hours of sun. Help!
Howard County Maryland
We suspect that your Knock Out Roses are infested with rose slugs. These are the larvae of sawflies. There are three types. See our website for information and control options in the Plant Diagnostics by typing 'rose slug' in the search box there.
The rose slug populations are high this year. Some rose slugs feed under the leaf, so you need to ensure that your spray is covering the underside of the leaf.