Integrated Management of Blueberry Diseases

Viruses and Phytoplasmas

Blueberry Shoestring Disease

This viral disease was originally described in New Jersey. In Michigan, the disease has been found in 0.5% of the bushes; however, an assessment has not been done for potential losses due to the virus.

The most common symptom is an elongated reddish streak along the new stems. The leaves may also show red banding or a red-purple oak-leaf pattern. Diseased leaves are narrow, wavy and somewhat sickle-shaped. Flowers may be red-streaked, and berries turn purple prematurely. Within a few years, berry production drops dramatically 

Management

Other than buying disease-free plants, destroying wild plants near the planting, and removing diseased plants, controls do not exist. As with most virus diseases, the best controls are preventing disease introduction and detecting the disease when it is still localized in a small portion of the field. The virus has been observed most often in the cultivars "Burlington", "Jersey", "June", "Cabot", and "Rancocas". Other cultivars may possess field resistance to the disease.

Blueberry Stunt

This disease was originally thought to be caused by a virus, but is now known to be caused by a phytoplasma. The only known carrier is the sharp-nosed leafhopper, though other vectors probably exist.

Symptoms vary with the stage of growth, time of year, age of infection and the variety. Symptoms are most noticeable during mid-June and late-September. Affected plants are dwarfed with shortened internodes, excessively branched and low in vigor. Small downward cupped leaves turn yellow along the margins and between the lateral veins, giving a green and yellow mottled appearance. These mottled areas turn brilliant red prematurely in late summer, although the midrib remains dark bluish-green. Fruits on affected bushes are small, hard, lack flavor, ripen late if at all, and remain attached to the plant much longer than on healthy plants.

 Mangement

Planting virus-indexed plants is helpful. Diseased bushes cannot be cured. They must be removed from the field as soon as they are diagnosed. The removal process may facilitate the further spread of the disease in the field. Agitation of the bush during removal will dislodge the leafhoppers, causing them to move to a neighboring healthy bush. Therefore, infected bushes should be sprayed with an appropriate insecticide prior to removal. The cultivars "Bluetta", "Jersey", and "Weymouth" are particularly susceptible, whereas "Rancocas"is resistant.