Answer: It sounds like either alternaria leaf spot or squash mosaic virus disease, says tom Gordon, horticulturist at Johnny's Selected Seeds in Albion, Maine. Both diseases are very common on squash and pumpkins in the East. Alternaria fungus causes small, darkened leaf spots that slowly expand, eventually killing the whole leaf. Squash mosaic virus causes similar symptoms, and also stunts and deforms the leaves. Both diseases overwinter in seeds, weeds and plant debris, infecting young leaves in early summer, especially under humid conditions. To control these leaf diseases, you should rotate your crops (don't plant squash in infected soil for two years), remove and dispose of any infected leaves and vines and keep the plants healthy, says Gordon. Squash mosaic virus is spread by aphids and cucumber beetles. Controlling these insects will also help stop the spread of the disease. To prevent alternaria leaf spot, spray sulfur before each rain when the plant is young until fruit set, says Gordon.
Q&A Library Searching Tips