Among the boxwood blight scare come samples of pachysandra with small yellow leaf spots. And rightly so–landscape contractors and residential clients alike are worried that they have a disease in the lowly pachysandra that will move into their fancy boxwood garden. The most common disease of pachysandra is volutella blight, which is caused by the fungus Volutella pachysandrae. We definitely see our fair share of volutella blight in the Plant Diagnostic Laboratory, but recently several samples were submitted with atypical leaf spots. Of course the fear of boxwood blight brought them in, but the reality is that these plants were infected with alfalfa mosaic virus (AMV).
Symptoms of AMV on pachysandra include chlorotic (yellow) ring spots and blotches on the leaves. This virus is transmitted by the green peach aphid and at least 14 other aphid species. It is also transmitted via seed and mechanically via infected sap from damaged plants. AMV is a generalist and has a host range that includes over 600 plant species in 70 families, so be alert to other odd looking leaf spots in the landscape and vegetable garden.
This disease is not likely to kill the planting, so control is not usually necessary. For pachysandra, simply removing the symptomatic plants as they appear is the best approach. Remember, the virus moves in sap, so be careful not to wound the adjacent healthy plants as you eradicate the diseased ones. Lastly, insecticides to control the virus spread by killing those poor little aphids has not proven to be successful, so leave your pesticides in the shed!