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Integrated Management
of Blueberry Diseases
Stem and Foliage Diseases
Fusicoccum Canker (Godronia
Canker)
Fusicoccum is a fungus which infects
blueberry stems causing dieback and plant decline. Losses from this
disease can be serious. The fungus overwinters as mycelium in cankers
on living plants. Spores are released from March to July. Infection
probably occurs during this period. Spores are largely disseminated by
rainwater. New infections occur following rains throughout the time
tender new tissue is present and temperatures are between 50-72ºF. New
infections can occur throughout the growing season. Cold stress or
winter injury may play a part in increasing disease damage. Leaves turn
a reddish-chocolate color when dry and often hang on late into the
fall.
Symptoms of Fusicoccum canker
are similar to Phomopsis canker on blueberry. The most unique symptom
is a red-maroon-brown lesion centered around a leaf scar, with a
bull's-eye pattern obvious on the lesion. As the lesion enlarges, the
margin remains red and the center becomes gray and dies. On young (1E
year old) stems, extensive stem infections quickly lead to flagging and
dieback of the entire stem. On warm, dry days shoots will suddenly wilt
and die due to stem girdling.
Management
Sanitation is essential. Removal of infected canes from
the planting is critical for control. A dormant application of liquid
lime sulfur (5 gallons in 100 gallons of water) may be beneficial for
control. Varieties differ in their resistance to the disease.
Phomopsis Twig
Blight (Phomopsis vaccinii)
This disease may be the most
prevalent of the canker diseases. The fungus Phomopsis causes stem
damage similar to that caused by Fusicoccum.
Spores from old cankers are
released in the spring and, to a limited extent, in summer. Most spores
are released from bud swell to petal fall. None are released after
September 1. Rain is necessary for spore release; temperatures ranging
from 70-80ºF encourage infections. The disease is most severe after
winters in which mild spells are interspersed with cold periods.
Periods of hot, dry weather during the growing season probably
predispose the plants to infection. The fungus overwinters in infected
plant parts.
Symptoms first appear on
smaller twigs. The disease then spreads into larger branches and may
affect the crown. It is possible for Phomopsis to spread downward in
injured canes to the crown and then progress upward on new canes. This
is rare and usually only occurs where the crown itself has been
injured, after a particularly severe winter, or in highly susceptible
cultivars. Young tissue initially shows no symptoms, then exhibit rapid
wilting and dieback. Lesions, somewhat similar to those caused by
Fusicoccum, but generally lacking the bull's-eye pattern, may appear on
the stems. Leaf spots also have been observed where disease is
particularly severe. The disease will cause premature ripening of the
berries. "Earliblue", "Coville", "Bluecrop", "Blueray","Jersey", and
"Berkeley" are susceptible to the disease. "Weymouth"may be the most
susceptible cultivar.
Management
Since mechanical damage and cold stress seem to be
necessary for Phomopsis infection, avoid careless pruning and
cultivating, and do not fertilize late in the summer. Pruning the
weakest canes to the ground is best for long-term production of the
bush. Keep the plants well-watered through prolonged periods of dry
weather in the summer. Avoiding stress will help prevent this disease.
Dormant sprays of lime sulfur (5 gallons in 100 gallons water) also
help to reduce inoculum of the pathogen. A fall application can be made
when most of the leaves have dropped. Spring applications should be
applied early, before warm weather occurs, or injury may result.
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