Hairy nightshade (Solanum physalifolium) is an annual weed found in a variety of habitats including cultivated fields, roadways, overgrazed rangeland, flowerbeds and vegetable gardens. The most common annual nightshade, hairy nightshade is considered poisonous. The toxicity varies based on the environment, plant part, degree of maturity and genetic makeup of the individual plant. The greatest toxicity is present in the seedlings, growing tips and immature berries. Commonly found in potato fields, hairy nightshade is not affected by the desiccant sprays used to kill potato vines and benefit by not having to compete for sun, water and nutrients once the vines are killed. Hairy nightshade is a host for many plant pests such as Colorado potato beetle and the late blight fungus. They may cause insect, disease and nematode problems to increase in potatoes and other rotation crops.
Hairy nightshade has slender stems that are often coated in sticky, spreading hairs and typically reach 1 to 2 feet, but sometimes 3 feet in height. Leaves are egg to lance shaped and between 0.75 and 3 inches in length. They have fine, spreading hairs on the undersides of large veins and sometimes on leaf surfaces. Leaf margins are lightly toothed or untoothed. The flowers are star-shaped with five fused petals and a yellow cone of yellow anthers. Flowers are clustered in groups of four or five. Berries are yellow green to olive when immature and purple-green when mature. They are 0.2 to 0.4 inches wide, and each contains 10 to 36 seeds.
Integrated pest management options:
Cultural: Crop rotation is necessary in controlling hairy nightshade. Moving out of potatoes allows the use of a variety of herbicides that are not possible when growing potatoes. The focus of cultural control should be on reducing the seed bank in the soil.
Mechanical: Mowing, tillage, and hand pulling over several years helps eradicate hairy nightshade if done before seed production.
Biological: There are no known biological control agents for hairy nightshade.
Chemical: Several chemical herbicides are available to control hairy nightshade. A complete list of approved chemicals is available on www.pnwhandbooks.org. Type “hairy nightshade” in the search for recommendations. Always read and follow herbicide label directions!
Tom Jacobsen is a University of Idaho Extension horticulture educator in Fremont County. He can be reached at 208-624-3102 or tjacobsen@uidaho.edu.
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