WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Blueberry Scorch Virus

Diseases

 

Scorch

Symptoms

Blueberry scorch virus (BlSV) is a serious disease of blueberries. Symptoms are indistinguishable from those observed in Blueberry Shock infected plants. In some cultivars, sudden and complete death of leaves and flowers can occur. Twigs can die back 2-4 inches (5 to 10 cm) and severe infections can kill the bush. The plant usually retains the scorched blossoms into the fall. Once bushes are infected with scorch virus, the plant will continue to decline in health resulting in significant yield loss and eventual mortality. Plants can be killed from blueberry scorch virus in 3-6 years. Blueberry scorch virus has a high potential to impact growers’ ability to produce blueberries. Symptoms may be confused with abiotic problems such as frost or other blossom blights.

Blueberry scorch virus was first identified in Washington and Oregon in 1980. This new virus was very limited in distribution and posed little risk due to low virulence. In 1988, a similar but more virulent disease was identified in New Jersey. A third strain was identified in British Columbia in 2000. This strain of blueberry scorch virus in British Columbia is more virulent than the original Pacific Northwest strain identified in 1980. Blueberry scorch virus is also known to occur in cranberries in Northwestern Washington and British Columbia.

 

Blueberry Scorch Virus - Two Leafs

 

Life History

Aphids are believed to be the primary source of virus transmission. Aphid transmission to a healthy plant occurs within fifteen minutes of feeding on an infected plant; aphids do not transmit the virus between longer periods of non-feeding.  Key periods of transmission are related to adult aphid flight. Active flight of aphids generally occurs in spring and late summer. Once a field is infected, spread can occur by aphids moving on machinery such as mechanical harvesters. Scorch virus is also subject to spread through nursery stock and movement of living plants from infested areas, including adjacent cranberry bogs. This is most likely the route of spread over long distances.

Blueberry scorch virus infected plants can remain asymptomatic for 1 to 2 years. Do to this long latency period, BlSV can remain unnoticed in fields until it establishes unless continual monitoring is performed. Although the plant is asymptomatic, it can serve as a reservoir for transmission to other plants. Symptoms appear during early bloom. Blossoms blight and turn brown then gray. New growth can blacken and die back. Leaves can develop oak leaf patterns of red and yellowing margins. Symptoms can first appear on few stems at first but will spread in the following years. Yields can drop rapidly as plant health declines. Not all varieties show symptoms of BlSV, some varieties are asymptomatic and can serve as reservoirs of the disease. Virus is present throughout infected plants.

 

Scorch

 

Monitoring

Because of long latency periods and asymptomatic varieties, BlSV can only be identified using molecular testing techniques. Monitoring for symptoms alone cannot detect BlSV early. Monitoring for BlSV can be coordinated with blueberry shock virus monitoring.  See the Sampling Guidelines for Blueberry Scorch Virus (pdf) for more information about sampling.

During early bloom visit plants that appear low in vigor and historically produce low yields. Collect tissue from fully expanded leaves for virus testing. Develop a labeling system that will allow you to match up bushes with tissue samples. It is important to be able to find the infected plant if tissue analysis produces a scorch virus positive. Flag plants that have been tested.

When scorch has been discovered in a specific field, increase the number of bushes sampled per site and increase the number of sites per field. Pay particular attention to new fields planted with stock from infested regions and fields adjacent to cranberry bogs.  Continue to visit plants with symptoms throughout the growing season.  Plants infected with blueberry shock virus will recover while planted infected with blueberry scorch virus will not.  These plants will continue to decline in health.

 

Thresholds and Management

No threshold exists for this disease.  At any positive test, the infected plants and roots should be removed immediately as well as 6 adjacent plants within the row.

Currently, virulent strains of blueberry scorch virus are limited to cranberry bogs in Washington State.   To avoid infestation in a field, plant certified stock from a reputable propagator. 

If virus is identified in fields, continue tissue sampling and plant tracking programs. Initiate intensive rouging of infected plants. Implement rigorous aphid management programs for at least two years following virus management.

 

Resources

Pest Alert and Fact Sheet: Blueberry Scorch Virus; USDA Horticultural Crops Laboratory.
http://www.geocities.com/martinrr_97330/BlSVweb/Pestalert.htm

Blueberry Scorch Virus; British Columbia Ministry of Agriculture and Lands
http://www.agf.gov.bc.ca/cropprot/blsv.htm

Oregon State University Extension, An Online Guide to Plant Disease Control, Blueberry Scorch
http://ipmnet.org/plant-disease/disease.cfm?RecordID=187

 

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • 360-676-6736 • whatcom@wsu.edu