Gray Mold

Gray Mold -Botrytis cinerea

Gray mold is a disease of potato foliage and tubers caused by the fungus Botrytis cinerea. The pathogen has a wide host range with reported incidences in more than 200 different hosts, some of which are used in rotation with potatoes. This wide host range causes a drastic increase in inoculum levels over time.

The pathogen requires moist conditions in order to infect. Airborne spores carried by wind and rain infect ageing potato floral parts and leaves, particularly late in the growing season. The pathogen may also cause tuber rot.

Gray mold is sometimes mistaken for late blight or early blight, but the grey-black to brown botrytis lesions on leaves and occasionally on stems will produce a characteristic greyish growth of mycelium and spores. Dense crop canopies greatly increase infection, especially on senescing or previously diseased plant parts. Heavy dew, fog, and frequent rain or irrigation increase gray mold severity.