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Lowbush Blueberry
Fact Sheet
Botrytis Blight
of Lowbush Blueberry
Introduction
Botrytis blight may be a serious problem in blueberry fields,
particularly along coastal areas of the Province or during the
bloom period if there are periods of persistent wet weather.
The disease is caused by the fungus Botrytis cinerea Pers.
This fungus has an extremely large host range including weeds,
cereals, berry crops, vegetable crops, ornamentals and forage
crops. In Nova Scotia, losses of 30 to 35% have been recorded
in lowbush blueberries because of Botrytis blight.
Infected
blueberry clone
Click picture to enlarge
Symptoms
The fungus may attack blossoms, fruit and leaves. Leaves may
also become infected by contacting diseased tissue. Leaves turn
light brown in colour and may become covered with the characteristic
gray mould. Infected flowers turn brown and shrivel up. During
damp weather the gray mould can be seen on the infected tissue.
Entire flower clusters can be destroyed and young green fruit
may be infected by contacting infected blossoms or blossom parts.
Gray
mould on infected blossom
Click picture to enlarge
Life
Cycle
The infection cycle
of Botrytis on lowbush blueberry is not well understood.
Research findings to date indicate that the fungus overwinters
on infected weeds within and outside the blueberry field. During
periods of wet weather in the spring the fungus produces spores
on the overwintering diseased tissue and are wind blown to developing
blueberry blossoms. The length of time necessary to establish
infections is not known, but outbreaks of the disease are associated
with several days of wet weather during bloom. The number of
disease cycles and thus the severity of disease is dependent
upon the number of wet periods that occur during bloom and shortly
after bloom. Infected corollas (petals) may drop and become
attached to other plant parts (i.e. leaves and other flowers)
and thus new infection sites are established. Young green fruit
may be infected by contact with infected blossoms.
Infected
flower clusters
Click picture to enlarge
Early blueberry
clones are the first to become infected because they come into
bloom first. Given wet, humid conditions, the fungus can become
well established on these early flowering clones and be a source
of infective spores for later flowering clones. Spore populations
tend to be low in spring reaching a peak during bloom. Strangely,
they remain high through the summer with spores being produced
on previously infected blueberry and weed tissue but blueberry
tissues are no longer susceptible. The following year very few
spores are produced on the blueberry debris because the nutrient
sources in the infected tissue have been used up. For this reason,
weeds appear to be the important initial source of the fungus.
Infection
cycle of Botrytis cinerea
Click picture to enlarge
Control
Strategy
Growers should monitor early flowering clones in their fields
for Botrytis infections. It is possible to observe the build
up of disease. If the disease is evident at mid bloom and wet
conditions are predicted, a suitable fungicide should be applied
prior to the wet period. Further sprays at 7 to 10 day intervals
may be necessary if damp weather persists through the bloom
period.
Burn-pruning every
second or third crop cycle will reduce overwintering Botrytis.
Control weeds within and surrounding blueberry field. Weeds
that have been observed to be sources of disease are Bunchberry,
Sheep Sorrel, Goldenrod, Pearly Everlasting, Potentilla
sp., and some grasses. Frost and herbicide damage appears to
increase the susceptibility of weeds and blueberry to Botrytis
infection.
Prepared by: Rick Delbridge, Plant Pathologist
Nova Scotia Department of Agriculture and Marketing and
Paul Hildebrand, Plant Pathologist, Agriculture & Agri-Food
Canada
January,
1995
Updated January
16, 2001
This page and all contents Crown copyright © 1997, Province
of Nova Scotia, all rights reserved.
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