Figure 1. Blighted blossoms Photo credit: Carolyn Teasdale, E.S. Cropconsult	Figure 2. BlScV infected bush next to healthy plants Photo credit: Carolyn Teasdale, E.S. Cropconsult

Blueberry Scorch Virus Strains

• 7 strains of BlScV have been found in B.C. These are found to be different from but related to the Northwest strain (found in Oregon and Southern Washington) and the East Coast strain, first identified in New Jersey over 25 years ago.
• Symptomology and susceptibility of blueberry varieties to individual strains is not well understood. Further research is being conducted to understand the individual strains affect different blueberry varieties.

Where has the virus been found?

• BlScV is present in all blueberry production regions, including all areas of the Lower Mainland/Fraser Valley, the Saanich Peninsula of Vancouver Island, and the Okanagan and Kootenay Valleys.
• BlScV has been found in both young fields and in older fields.

Symptoms

• The best time to look for symptoms of blueberry scorch is during bloom. Monitor your fields carefully at this time.
• In the most severe cases, blossoms and leaves rapidly blight and dry up following early bloom. Sometimes only blossoms are blighted, or only a few infected shoots may be observed.
• Blighted blossoms and leaves remain attached to green stems.
• Blueberry scorch symptoms can resemble blueberry shock, mummy berry, frost damage, bacterial blight, spanworm damage or other diseases. Laboratory testing is required for a proper diagnosis.
• Symptoms usually develop 1-2 years after infection. This period is called the latent period (the length of time it takes for the virus to build up to detectible levels in the plant following infection).
• Symptomless plants are often found next to diseased ones.
• BlScV infected plants decline and die-back over a period of years.
• Infected plants never regain normal productivity.
• As the season progresses, plants may put out new growth that appears to be healthy, but remain infected with the virus.
• In some cases, infected plants may show few or no symptoms, but all varieties are susceptible to infection.
• 'Bluecrop' plants may show only subtle symptoms, or show no symptoms at all. Infected 'Bluecrop' foliage may be a paler green than that of healthy plants. They do not usually show the blighting and dieback symptoms that are more common with other varieties. Although symptoms on these bushes may be slight, the infected bushes have lower yields. They produce fewer blossoms and smaller fruit.
• Other signs of infection can include red line patterns on leaves (oak leaf patterning) in the fall, yellowing of leaf margins, leaf mottling, overall pale color, low number of blossoms, or even a ‘twiggy’ appearance. If anything looks suspicious, have it tested.
• All parts of the plant become infected, even the roots. If an infected plant is mowed down, the new shoots will still be infected with the virus.

Figure 3. Blossom blighting	Figure 4. Leaf blighting on ‘Northland’ variety
Figures 5 and 6. Healthy ‘Bluecrop’ (left) versus Scorch Virus infected ‘Bluecrop’ (right). Note the lack of fruit and pale leaf colour on the infected bush. Photo credit (Figs. 3-6): Sonja Ring, BCBC.

Figure 7. Regrowth on mowed BlScV infected plants. The new shoots will act as a source of infection as long as these plants remain in the field. Photo credit: Sonja Ring, BCBC.	Figure 8. Infected ‘Bluecrop’ plants that are slightly yellower than surrounding, healthy plants. Photo credit: Carolyn Teasdale, E.S. Cropconsult.

Management Strategies

1. Monitoring. All blueberry fields should be carefully monitored starting at bloom time for blossom and shoot blighting and other scorch-like symptoms.
2. Test plants with any suspicious symptoms. Send leaves from suspicious plants to the Ministry of Agriculture Plant Health Laboratory (or other qualified lab) for testing to confirm whether the virus is present. Collect at least 10 fresh leaves per bush, as close to the affected (symptomatic) region as possible. BlScV samples submitted to the lab must be accompanied by a BlScV laboratory submission form. Growers can submit up to 10 samples per field, free of charge.
 
3. Remove infected plants. Infected plants should be removed as soon as possible and destroyed. Infected plants should be removed entirely including roots. Infected plants that are left in the field will act as a source of virus infection for surrounding, healthy plants. In the absence of plant removal and/or aphid control, the virus can spread through a field at a rate of 5% per year. Whole fields will eventually become infected and non-productive.
4. Aphid control. BlScV is transmitted by aphids (vector). In growing regions where scorch is present, all growers should follow an effective aphid control program. All fields should be treated before bloom with a registered aphicide to control the over-wintering aphids before they reproduce and disperse. After bloom, monitor fields for aphids and, if necessary, apply aphicide before populations increase. Scout several locations in each field, especially around field borders. Do not spray until after bees have been removed from the field, and be sure to follow pre-harvest intervals as indicated on the aphicide labels. Refer to the BC Berry Production Guide for further information on pesticide recommendations and management of aphids.
   The following products are recommended for aphid control for use in 2011:
   Fulfill (50% pymetrozine) at 193 g/ha (77g/acre) for overwintering aphid control prior to bloom. Fulfill can be used post harvest if aphid population increases. Do not apply more than twice per season. Do not apply within 85 days of harvest.
   
   Assail 70WP (70% acetamiprid) at 56 to 86 g/ha (22 to 34 g/acre). Do not apply more than 4 times per season. Allow 12 days between applications. Do not apply during bloom as Assail is toxic to bees. Do not apply within 7 days of harvest.
   
   Concept Liquid (75 g/L imidacloprid, 10 g/L deltamethrin) at 560 mL/ha (224 mL/acre) as foliar spray in enough water to ensure good coverage. Apply post bloom after bees have been removed from the field and up to 14 days before harvest. Do not apply more than 3 times per season.
   
   Actara 25WG as used for weevil control will also provide effective control of aphids.
   
   Contact the Ministry of Agriculture or your chemical supplier for up-to-date information on pesticide registrations and use restrictions. Refer to the BC Berry Production Guide for further information on product recommendations and management of aphids.

5. Start with clean plants. Do not propagate infected plants. All mother plants should be tested for BlScV prior to propagating. Aphid control is critical throughout all phases of propagation to prevent virus introduction and spread. Only purchase planting stock from reputable nurseries that follow an accepted propagation protocol, including virus testing.

Blueberry Scorch Virus is a very serious disease that is widespread in all blueberry production regions of B.C. With over 18,000 acres of blueberries now planted in B.C., management and control of BlScV requires region-wide cooperation of all growers to control aphid populations and remove infected plants in order to slow the spread of blueberry scorch within fields, between fields, and between farms.

Remember:

1. Monitor fields for scorch virus symptoms, especially during bloom
2. Sample and test any plants with suspicious symptoms
3. Remove all infected plants
4. Maintain an effective aphid control program
5. Only purchase planting stock that has been grown according to an accepted propagation protocol that includes virus testing.

Further research is being conducted in order to gain a better understanding of the disease, develop better testing methods for detecting the virus strains and improve management strategies.

For further information on Blueberry scorch virus, contact:

Karina Sakalauskas, BC Blueberry Council
(604) 613-2133

Siva Sabaratnam, Ministry of Agriculture
Mark Sweeney, Ministry of Agriculture
(604) 556-3001

BC Blueberry Council
Abbotsford, B.C.
April, 2011