Fruit IPM Factsheet Fruit IPM FactsheetBLUEBERRY SHOESTRING VIRUS
IN MICHIGAN
ADAPTED from E-1731
& Compendium of Blueberry and Cranberry Diseases from APS Press
By: Mark Longstroth
Shoestring disease is the most important virus disease of Michigan blueberries. It is present in many older Michigan blueberry fields. Annual losses are estimated at several million dollars due to bush and crop loss.
Symptoms and Disease Cycle: Shoestring is named for one of the symptoms associated with the disease; some leaves on infected bushes are strap-like (shoestring symptom). Usually a few clusters of leaves in the crown will show this symptom. Some will be misshapen in the form of crescents, or twisted. The most reliable symptom is narrow, elongated reddish streaks, 1/4-to-1-inch or longer on current year and 1one-year old stems. Often, the fruit on infected bushes is a reddish-purple color, instead of the normal blue color.
The disease occurs naturally in the wild Michigan Blueberries. About 12 to 50% of the wild highbush blueberries and 6 to 13% of lowbush blueberry clones were found to be infected in a survey of Michigan.
The virus is spread from bush-to-bush by the blueberry aphid Illinoia pepperii.
This aphid spends its entire life on blueberry plants. The aphid overwinters as eggs on
the blueberry plant. In the spring and during the growing season the aphid colonizes the
growing shoot tips. In the late summer and fall a low percentage of winged aphids appear
and colonize new bushes.
Ground-applied sprays are much more effective than aerially-applied
sprays. Apply the first spray in early to mid-June when the first aphids are found on the
succulent shoot terminals growing from the crown. 
Apply
follow-up sprays at two or three week intervals if aphids begin to increase. Good spray
coverage is essential. Consult the Michigan Fruit Management Guide Extension Bulletin E-154
for insecticides and rates.
The disease spreads down the row as aphids move from plant to plant.
Aphids are also spread by Mechanical harvesters that can carry the aphids to other rows
and fields. There is a 2-to-4-year latent period in the field before an infected
bush shows symptoms. Once plants are infected there is no cure.
Control: Use disease-free planting stock. Blueberry cultivars such as Jersey,
Rubel, Burlington, Earliblue, Rancocas, Weymouth and the Blueray are quite susceptible to
the disease. Bluecrop has good field resistance and is planted where disease pressure is
great. In fields where infected bushes exist, the following control program should be
followed: Inspect all bushes. Remove those showing symptoms, and replant with healthy
stock. Keep the blueberry aphid down to near zero population by using well-timed aphicide
sprays.
In cool springs, Virus infected plants will often show symptoms of the disease. In 2003 we had a long cool spring. The cool weather has made virus symptoms apparent in many older fields. The normal Shoestring Virus symptoms in blueberries are small strap-like leaves and reddish streaks on young shoots. This year we are seeing a red stain, associated with the leaf veins in the center of the leaves, that resembles a red oak leaf. I took a lot of pictures and these are some of the best.
In cool weather, we see a red stain that resembles a red oak leaf.
Strap-like leaves associated with shoestring disease.This is the most
common symptom observed in the growing season. These thin leaves look like shoestrings and
give the disease its name.
Red flowers
Red streaks on the cureent seasons growth.
This picture shows a multitude of symptoms; the red oak leaf pattern, the
small, strap-like leaves and Elongated reddish streaks on blueberry
stems. The stem streaks are the most reliable symptom of shoestring disease.
Below are Figures from E-1731
Crescent-shaped and deformed leaves associated with shoestring virus.
Elongated reddish streaks on blueberry stems. This is the most reliable
symptom of shoestring disease.
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