Blueberry scorch, shock and sheep pen hill virus quarantine

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

In 2002, the Michigan Department of Agriculture (MDA) established a quarantine for blueberry planting material to prevent the introduction into Michigan of blueberry scorch virus (BlSV), blueberry shock virus (BlShV), and Sheep Pen Hill virus (BlSV-NJ). These viruses are known to infect blueberries in Oregon, Washington, New Jersey and British Columbia (Canada). Cranberry plants can also be infected by blueberry scorch virus. Recently, blueberry scorch virus was also found in highbush blueberries in Connecticut and Massachusetts. These viruses spread from one geographic location to another over long distances through infected planting stock. To date, these viruses have not been found in Michigan, and it is therefore very important that we are vigilant and keep them out as they can wreak havoc on our blueberry industry.

Blueberry scorch is caused by the blueberry scorch virus and has a devastating effect on blueberry plants. In the spring, young flower clusters and shoots suddenly turn brown and die (Photos 1, 2). Blighted flower clusters and shoots can be confused with mummy berry and Botrytis blight. The disease starts on one or two branches before it spreads to the whole bush in succeeding years. The symptoms are expressed in infected plants every year and plants do not recover. The production begins to drop off rapidly and the bush eventually dies. Neighboring bushes often appear healthy. Some cultivars also show marginal leaf chlorosis (Photo 3). The Sheep Pen Hill virus is a strain of blueberry scorch virus that occurs in New Jersey. Symptoms are similar for both strains, except that a red line pattern is sometimes seen on leaves of bushes infected by the Sheep Pen Hill virus (Photo 4). The disease can spread rapidly throughout a planting due to movement of aphids, which transmit the virus. Aphid transmission occurs over relatively short distances (less than a mile). All cultivars can be infected by blueberry scorch virus, but some do not show symptoms. Symptom-less infected bushes can still serve as a source of infection for nearby bushes.

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Photos 1 & 2: Young flower clusters and shoots turn brown and die due to blueberry scorch virus. Photo credit: Bob Martin.

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(Left) Photo 3: Marginal leaf chlorosis. Photo credit: Bob Martin. (Right) Red line patterns on leaves caused by Sheep Pen Hill virus. Photo credit: Bob Martin.

Blueberry shock, caused by the blueberry shock virus is very similar to blueberry scorch in its symptoms, including a sudden blighting of blossoms and leaves (Photo 5). However, the plant then apparently recovers and produces a second flush of leaves. By the end of the season, the bush looks normal except for the absence of fruit. The plant may exhibit this “shock” reaction for one to three years and may be symptom-free thereafter, but will carry the virus. All cultivars are susceptible. Blueberry shock virus is pollen-borne. Transmission of the virus occurs when pollinators, especially honeybees, transfer infected pollen to flowers on healthy plants.

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Photo 5: Sudden blighting of blossoms caused by blueberry shock. Photo credit: Bob Martin.

The MDA quarantine regulations stipulate that no plants, buds, vegetative cuttings or any other blueberry planting material should be brought into Michigan from regulated areas (WA, OR, NJ, BC) unless it has been certified virus free by a virus-free certification program recognized by MDA. Planting material shipped into Michigan must be accompanied by a State Phytosanitary Certificate or Certificate of Quarantine Compliance, indicating its point of original propagation or production and labeled or stamped to show compliance with terms of this quarantine. Violations of the quarantine regulations can lead to fines and destruction of uncertified or virus-infected plant material as well as revocation of the special permit to ship to Michigan.

Dr. Schilder’s work is funded in part by MSU‘s AgBioResearch.

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