Anthracnose (Elsinoe ampelina): Anthracnose is a
fungal disease that can be very destructive to grapevine shoots and fruit,
particularly in wet seasons. It overwinters as sclerotia on grape canes that
were infected in the previous season and in fallen mummified berries. In the
spring, the sclerotia produce spores after a period of wetness that is 24
hours or greater in length and temperatures above 36°F. With free moisture
from rain or dew, the spores germinate on the tissue and start an infection.
Symptoms of infection can show up as quickly as 4 days (at 90°F) to up to
two weeks (at 36°F). The most favorable conditions for disease development
are warm temperatures and heavy rainfall. This disease is most prevalent in
the Eastern half of Texas and in wet seasons. Blanc Du Bois is considered to
be highly susceptible to this disease.
Anthracnose shoot infections first appear as reddish colored spots that
enlarge and become sunken lesions that turn brown with gray centers. Infected
shoots often remain stunted and may die if multiple lesions coalesce. Leaf
infections begin as small, circular brown spots that turn grey. The center of
the lesions often drops out giving the leaf a shot-hole appearance. Severe
infections can cause leaves to be distorted and even die. Cluster infections
can occur before bloom and if lesions girdle the rachis, a portion or even all
of the flower cluster dies. Berry infections first appear as small reddish
brown circular spots that enlarge to approximately 5-7mm across and may become
slightly sunken. The center of the lesions turns gray giving them a “bird’s
eye” appearance.
If possible infected wood should be pruned out and destroyed, and if
significant numbers of previously infected berries exist on the vineyard floor
they can be covered with cultivation. As with all fungal diseases, improving
airflow through the canopy with proper vineyard design and canopy management
can enhance control by reducing fruit and foliage drying times after rainfall,
and increasing fungicide spray penetration.
Fruit
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Shoots
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