Latin name: (no Latin name)
Reason for Concern:
1) A serious disease threat that can result in complete yield losses on infected plants.
2) Once infected with scorch, plants do not recover; yields decline over time and blight symptoms appear year after year.
3) Can spread by as much as 5% annually in infected fields.
Symptoms may not develop for one or more years following infection. Symptoms usually appear during bloom with the disease starting on 1 or 2 branches before it spreads throughout the bush in succeeding years. In infected plants, the flower clusters blight just as the petals are opening; young shoots may blight also, turning grayish black. Blighted tissues may remain on the twig and can be observed the following year, but this is not a reliable symptom, as it varies between varieties. Other symptoms include leaf chlorosis (pale coloring), blighting of young leaves and dieback. Less conspicuous symptoms include red line patterns on the leaves of some infected cultivars in October, yellowing of leaf margins and yellow leaf mottling. Symptoms on Bluecrop are less obvious than on other cultivars and include chlorosis, lack of blossoms and a resultant yield reduction. In some cultivars, a sudden and complete death of flowers and leaves occurs, while others remain symptomless. Twigs may die back 4 to 10 cm. Severe infections can kill the bush.
The virus is spread by aphids that feed on infected plants before moving to one that is health. The virus spreads through a field in a radial pattern from a point source, with the rate of spread dependent upon the number of aphids. Eventually all bushes in a field may become infected, as well as neighboring fields. The virus does not replicate in aphids and must be transmitted fairly quickly to new plants in order to survive. Most infections occur from mid-April to early-August.
- During bloom, the flower clusters blight (turning brown and collapsing) just as the petals open. Young shoots may blight also, turning grayish black.
- Blighted tissues may remain on the twig but this is not a reliable symptom as a host of other viruses and infections can cause similar symptoms.
- Blight symptoms appear year after year spreading to neighboring bushes. When scouting, age of planting, variety, location, weather, and proximity to areas where known Scorch has existed should all be considered.
- To correctly identify the virus causing the symptoms, contact your local extension office to arrange for sending in a sample to be tested.
- The symptoms of this virus can be confused with the much more common but less serious Shock Virus. Go to (Oregon State University Online Guide) for a description of other blueberry viruses.