Two ringspot viruses infect blueberries: the tomato ringspot virus and the tobacco ringspot virus. The disease caused by tobacco ringspot virus is often called necrotic ringspot. The symptoms, biology and management of the two viruses are very similar.
Both viruses cause blueberry leaves to become small and distorted, cupped leaves, often with a mottle of light green and dark green. Small brown spots (< 1/4 inch) can also form on leaves and stem. Virus infection causes blueberry plants to lose vigor and decline. Plants with either ringspot virus have low yields, are often stunted and are more susceptible to winter injury. The severity of the disease varies among blueberry cultivars, with some cultivars can be severely injured by the viruses while others show few or no symptoms. The relative susceptibility of Minnesota cultivars has not been determined.
Both ringspot viruses are primarily spread by the dagger nematode, which is common in many parts of Minnesota. Dagger nematodes are microscopic worms that live in the soil, and feed on the roots of blueberries and other plants. Nematodes acquire the virus by feeding on infected plants, including susceptible weeds like dandelion, chickweed or common plantain. Once a nematode acquires a virus, it can spread the virus to other plants, including other blueberries.
Virus diseases can be minimized by planting certified plants from an established nursery. Maintaining good weed control will help the virus from spreading to other plants. Diseased blueberry plants can be removed, but the disease can continue to spread in the soil even after infected plants have been pulled.