Q: What is wrong with my viburnum? There are spot on the new leaves only.
A: Thanks for bringing in clippings from your plant. I was not sure about this so I sent photo samples off to the University of Florida Pathology Department in Gainesville. I was not able to discern the problem initially as I could not locate any fungal spores or insect bodies. One of my fellow agents from Southwest Florida, Jim Moll, had the same problem and e-mailed me immediately. It is so wonderful to have such a fine network of knowledgeable professionals watching my back.
The problem is a very tiny insect called thrips. By the way, they are called thrips whether there is one or a thousand. Thrips scrape the plant tissue rather than pierce into the leaves and suck the fluid. The damage will show a browning of the plant tissue similar to a scar once the upper layer has been removed. The reason I was not able to locate any insects was they are residing in the flowers. Once I knew to look in the flowers and not just on the leaves the little critters were easy to find. I simply tapped the flowers over some white paper and sure enough I could see the tiny black adults and beige nymphs. There are several products available to control this insect so look for products with the active ingredient imidocloprid, pyrethroid or carbamate. You might try applying horticulture oil to the flowers too.