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Black
rot - Guignardia bidwellii
Annemiek
Schilder, MSU Plant Pathology |
| Home > Scouting guide> black rot |
On
the leaves, light brown, roughly circular spots appear in the spring
and summer ( left). These can be distinguished from herbicide
damage by a ring of small black fruiting bodies (above right), which are visible
with the naked eye or a hand lens.
Fruit infections occur
from bloom until the berries become naturally resistant (about 3 to 5
weeks after bloom in most varieties). The first symptom, a whitish dot within a rapidly
expanding brown area, appears 10 to 14 days after infection. Within a
few days, the berry starts to shrivel and becomes a hard, blue-black mummy. |
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| Initial berry lesions (above), which expand and may show growth rings (right). |
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| If berries are infected
close to the onset of natural resistance, lesions remain localized. The
fungus over-winters in mummies within the vine or on the ground. Ascospores
are released shortly after bud break until about 2 weeks after bloom and
are dispersed by wind and rain.
Infected tissues can also yield conidia, which are dispersed by rain
splash and cause secondary infections. The optimum temperature
for disease development is 27°C (80°F). At that temperature, the
wetness period required for infection is only 6 hours (see table below). |
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