Blueberry Shoestring Disease is caused by the blueberry shoestring virus (BBSSV). This is probably the most well-known and widespread virus disease of blueberry. Originally described in New Jersey, it is now found in several locations in North America. It has not been reported from other parts of the world. It caused over $3 million in losses in Michigan in 1981, and can cause a 25% loss of yield on infected bushes. Ripe berries are reddish rather than blue, causing an additional loss of quality.

Symptoms. The most common symptom of this disease is an elongated reddish streak (1/8" by 1/2" to 3/4") along new stems and 1-year-old stems. The streaks are most often found on the side of the stems exposed to the sun. Leaves are often narrow and elongated, with wavy edges. They may also be somewhat sickle shaped. Leaves may have red banding along the veins and midribs, or red-purple oak-leaf patterns. Many leaves on the bush may be affected, or just a few near the crown. Flowers may be red streaked or have pinkish to reddish petals (although this is the normal color of petals on the cultivar Blueray). The berries ripen prematurely, and are often reddish purple rather than blue. After a few years, berry production drops dramatically.

This disease is spread from infected plants to healthy plants by the blueberry aphid (Illinoia pepperi). Very few of these aphids are winged, so they usually move from one plant to the next by crawling along touching branches. Because of this, the disease spreads down the row, affecting several plants in one row, while the neighboring rows are disease-free. It takes four years from the time a plant is infected until it begins to show symptoms.

Prevention. There is no cure for this disease. It is best to exclude it from a production area by buying disease-free plants. Destroy wild plants near the production area. Remove and destroy any plants that become diseased. Wash any machinery that contacts plants to avoid carrying aphids from one area to another. See current recommendations for aphid control measures. Resistance is available for this disease.

Blueberry Stunt is caused by a phytoplasma. Stunt is an important disease of blueberry throughout the United States and Eastern Canada.

Symptoms.  Symptoms are most noticeable during mid-June and late September. Plants lack vigor and are stunted and excessively bushy, with shortened spaces between the leaves (internodes) and an abnormally high number of branches. The infected bushes can be less than half the size of healthy ones. Leaves are small and are cupped downward. Leaves are yellow along the edges and between the veins, giving them a mottled appearance. Yellow areas of the leaves will turn brilliant red early in the fall, before the leaves of healthy plants. Few berries are produced, and these are small, hard and tasteless. They ripen late, if at all, and will cling to the bush much longer than berries on healthy plants.

Stunt is spread from diseased to healthy plants by the sharp-nosed leafhopper (Scaphytopius magdalensis), and two other closely related leafhoppers. These leafhoppers also feed on pin cherry, black cherry, chokecherry, dewberry, wild raspberry, and blackberry.

Prevention. Plant disease-free plants. Remove diseased plants from the field as soon as possible and destroy them. Spray an insecticide to kill leafhoppers before removing plants to avoid disturbing the insects, causing them to go to other healthy plants and infect those. There are a few varieties that are resistant to this disease. See current recommendations for leafhopper control.

Red Ringspot is caused by red ringspot virus (RRSV). It is currently the most widespread viral disease in New Jersey, and was the cause of an estimated 25% crop loss in experiments in Michigan. RRSV may be the same as the virus that causes cranberry ringspot disease.

Symptoms. Red spots, rings, and oak-leaf patterns appear on older leaves in late June or July. The spots are usually 1/8" to 1/4" in diameter, and are most prominent on the top surface of the leaves. Similar spots can be found on branches older than a year. The berries are pock-marked and unattractive.  Some varieties may have light blotching on the fruit. Production is seriously decreased. Powdery mildew causes similar spots, but on both sides of the leaves.

This disease appears to be spread from plant to plant by mealybugs, although other insects may be involved. It is most commonly spread, though, by planting diseased stock.

Prevention. Plant disease-free stock. Remove and destroy infected bushes immediately. Resistance is available for this disease. There are no chemical control measures.

Witches'-Broom is caused by an unusual fungus, Pucciniastrum goeppertianum. It is included here because the symptoms are more like those of a virus than a fungal disease. It occurs in North America, Europe, Siberia, and Japan. This fungus spends part of its life on highbush and lowbush blueberry. The other part is spent on fir (Abies) trees. Both of these hosts must be present for the disease to occur.

Symptoms. The year after infection, diseased blueberry plants produce numerous swollen spongy shoots, with tiny leaves and shortened distances between the leaves (internodes). These "brooms" continue to grow this way each season and can live for many years. Many brooms can appear on one plant. Young growth of the brooms is yellow or reddish, but becomes brown and shiny, then dull, and eventually dry and cracked. The plants produce no fruit on these brooms.

Prevention. Do not plant within 1200 feet of fir trees. Eradicate diseased plants with a recommended herbicide to eliminate the disease from a field. Pruning off the brooms will not control this disease, as it is in the entire plant. Fungicides are not effective against this disease.

By Pamela S. Mercure, IPM Program Assistant, University of Connecticut

References:

Bristow, P.; R. Byther; R. Ingram and D. Ramsdell. 1992. Nematode and disease management. Chapter 9 in Highbush Blueberry Production Guide. M.P. Pritts and J. F. Hancock, eds. Notheast Regional Agricultural Engineering Service.

New England Small Fruit Pest Management Guide, 1996-1997. S. Schloemann, ed. University of Massachusetts Cooperative Extension System.

Nickerson, N.L. and F.L. Caruso. 1995. Witches'-Broom. pp. 26-27 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.

Ramsdell, D.C. 1995. Red Ringspot. pp. 58-59 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.

Ramsdell, D.C. 1995. Stunt. pp. 52-53 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.

Ramsdell, D.C. 1995. Shoestring. pp. 50-51 in Compendium of Blueberry and Cranberry Diseases. F.L. Caruso and D.C. Ramsdell, eds. APS Press, St. Paul, MN.


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