Hairy Nightshade, a Weed Susceptible to Potato Late Blight

Late blight, caused by the fungus Phytophthora infestans, is a devastating disease of potatoes. If left uncontrolled under cool, wet weather, it can destroy a potato field in a few days. The primary hosts of the late blight fungus are potatoes and tomatoes, but hairy nightshade, a weed belonging to the same family as potatoes and tomatoes (Solanacea), is also infected by the late blight fungus.

Hairy nightshade is an annual weed that germinates in early summer. Mature plants are about 60 cm tall. The foliage is spreading and covered with fine hairs. Plants feel clammy or sticky when handled. The flowers are white with yellow centers and look like potato flowers, but are only one fourth the size. The seed balls that form look like the green seed balls that form on potatoes, but they are also smaller. Seed balls turn yellowish-brown to brown at maturity.

This season, hairy nightshade has been observed growing along the edges of many potato fields and in hedgerows across the province. Potato scouts should look for this weed and destroy it wherever they find it. Otherwise, hairy nightshade infected with late blight could serve as a source of inoculum all season.