ANTHRACNOSE, BIRD?S-EYE ROT
Description
Symptoms
Disease Cycle
Control
Description:
Anthracnose is a disease of Vitis vinifera,
French-American hybrids, and Vitis labrusca (American bunch
grapes). Muscadine
grapes (V. rotundifolia) are not affected.
In the Southeast the disease is primarily important on American
bunch grapes, and is favored by the rainy and warm climate.
Epidemics are sporadic but can cause significant economic loss,
reducing fruit quantity and quality and weakening the vine, especially
once established in a vineyard.
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Symptoms:
Anthracnose infection is most
common on fruit and young shoots but may occur in all succulent plant
material. Fruit lesions are
small, circular, and red in color. As the lesions enlarge (up to ? inch
in diameter) and become sunken, the centers become gray (Fig.
1) and are
often surrounded by a reddish-brown margin, resulting in the typical
?bird?s-eye? symptom. Infected grapes often crack, leaving the
seed exposed (Fig.
1). If an early infection is arrested, the surface of
the fruit can appear scabby. On
shoots and leaves, lesions are similar in color, sunken, and have
reddish-brown borders. When the centers of the lesions drop out (?shot
hole?), leaves develop a ragged appearance. Young leaves are more
susceptible and can be malformed if veins are infected. Stem infections
can cause cracking of stems and formation of callus tissue, and
blighting or girding of shoots can occur if the lesions coalesce (Fig.
2).
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Disease Cycle:
Anthracnose is caused by the fungus Elsinoe ampelina.
The pathogen over-winters in old lesions and as fruiting bodies (sclerotia)
on infected canes. Sclerotia germinate in the spring after a 24-hour period of
wetness, producing mycelium and eventually spores (conidia). Fruiting
structures (ascocarps) can also form on infected debris to produce
ascospores. Conidia and ascospores, both serving as primary inoculum,
germinate and infect green tissue. Temperatures of 24 to 26 C (75 to 79
F) are optimum for infection. Clusters are susceptible to infection from
before flowering until veraison. Once the fungus is established in the
host, fruiting bodies (acervuli) form lesions that exude pinkish masses
of conidia. Splashing rains
spread the conidia to adjacent clusters resulting in secondary
infections.
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Control:
Cultural - Sanitation is very
important for anthracnose control. Since the fungus can survive on
canes, pruning out and destroying infected shoots, cluster stems, and
fruit during the dormant season reduces the amount of primary inoculum
for the disease in the vineyard. Canopy management that facilitates air
circulation and reduced drying time, including shoot positioning and
leaf removal, will also benefit disease control.
Chemical - Refer to the Winegrape Spray
Program in the North Carolina Agricultural Chemicals Manual for current
anthracnose control recommendations (http://ipm.ncsu.edu/agchem/chptr7/706.pdf).
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