Blueberry scorch virus (BlScV) was first found in B.C. in 2000, but it is likely
that BlScV was present in B.C. several years
earlier. It is now widespread in
all blueberry growing areas of the province. Severity of the symptoms depends on
the cultivar and viral strain, but all highbush blueberry varieties grown in
B.C. appear to be susceptible. BlScV
can cause
severe blossom and leaf blighting,
and decreased yields. Once infected, plants do not
recover. Infected plants show symptoms each year, and should be removed. BlScV is
spread by aphids or planting infected stock.
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| Figure 1. Blighted blossoms |
Figure 2. BlScV infected bush next to healthy plants |
Blueberry Scorch Virus Strains
- 7 strains of BlScV
have been found in B.C.
These are thought to be distinct from 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.
- BlSV has been detected in cranberry
(Vaccinium macrocarpon), red huckleberry
(Vaccinium parvifolium), and oval-leaf (wild)
blueberry (Vaccinium ovalifolium) but does not
appear to cause symptoms in any of these hosts.
Symptoms
- The best time to look for symptoms of BlScV 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.
- BlScV symptoms can resemble
Blueberry shock virus, 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 signs of infection, or show no
symptoms at all. Infected 'Bluecrop' may be more 'yellow' in colour than
healthy plants. They do not always show the dieback symptoms that
are more common with other varieties. Although symptoms on these bushes may
be slight, the 'yellowed' 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.
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| Figure 3. Blossom blighting |
Figure 4. Leaf blighting on ‘Northland’ variety |
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| 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. |
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| 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. |
Figure 8. Infected ‘Bluecrop’ plants that are
slightly yellower than surrounding, healthy plants. |
Management Strategies
- Monitoring. All blueberry fields should be carefully monitored
starting at bloom time for blossom and shoot blighting and other scorch-like
symptoms.
- Test plants with any suspicious symptoms. Send leaves from
suspicious plants to the BCMAL Plant Disease Diagnostic Lab
(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.
- 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.
- Aphid control. BlScV is transmitted by aphids.
An
effective aphid control program should be used by all growers. In growing
regions. 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 sprays 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 on the labels.
Information on registered aphicides and rates can be found in the
BCMAL Berry
Production Guide. An emergency registration for Fulfill 50WG (pymetrozine) has
been requested for 2008. Full
registration is expected for 2009. Admire 240F (imidacloprid) can be used
post-bloom, after bees have been removed from the field and up to 14 days
before harvest. Contact the BCMAL or your chemical supplier for up-to-date
information on chemical registrations and use restrictions. Full registration
of additional effective aphicides is being pursued.
- 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:
- Monitor fields for scorch virus symptoms, especially
during bloom
- Sample and test any plants with suspicious symptoms
- Remove all infected plants
- Maintain an effective aphid control program
- 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 virus, to develop better testing methods for
virus detection and to improve management strategies.
For further information on Blueberry scorch virus, contact:
Sonja Ring, BC Blueberry Council
(604) 613-2133
Siva Sabaratnam, BCMAL
Mark Sweeney, BCMAL
(604) 556-3001
BC Blueberry Council
Abbotsford, BC
February 2008
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