Disease(s) of Rosemary
For several years I have had disease in my Rosemary plants, none of which were within 20 feet of one another. The leaves turn light gray-green and under a microscope show something moving inside, about 1/6 - 1/8th of the length of the leaf or smaller (only an estimate from memory) Is someone expert enough to tell me what's going on and what to do about it? The plants are not attractive to say the least and appear very unappetizing. Thank you for being a resource to ask, even if no one knows what's going on, Fred Ruckdeschel
Montgomery County Maryland
Rosemary is susceptible to powdery mildew, root rot, and some insect pests. You can reduce the chance of mildew development by providing good circulation around the plants and avoid over-watering or wet soil. Spider mites can be a problem in rosemary too, but you would see stippling (small dots) and webbing if this were the case.
We recommend that you simply prune out any dead or damaged stems and allow for a new flush of growth. Prune again after the plants flower. This will stimulate additional new growth and branching.