Phomopsis (Phomopsis viticola): Phomopsis is a
fungal disease that can infect grapevine shoots, leaves, and fruit. The fungus
overwinters in infected wood, and in late winter and early spring, it produces
spores that are rain-splashed onto nearby grape tissue. During wet periods,
infections can occur at a temperature range of 41 to 96°F. Phomopsis can
occur across the state, but is particularly problematic during wet springs.
Symptoms of leaf infections appear as small light green lesions with irregular
margins. The lesions eventually turn dark brown to black with a yellow border,
and severe leaf infections may cause the leaves to be deformed. Shoot
infections appear as black, elongated lesions that may cause cracking. This
weakens the shoot and can result in shoot breakage under high winds. Crop loss
can occur when rachis infections result in girdling and a portion of the
cluster dies, or when berries themselves become infected. Rachis infections
may also result in cluster breakage, particularly during harvest and with high
wind. Grape berries that are infected with phomopsis often resemble black rot
mummies, but generally do not remain firmly attached to the cluster and do not
usually become evident until near harvest.
Sanitation is an important aspect of any phomopsis cane and leaf spot control
program. If possible all diseased and dead wood and any remaining fruit should
be removed during dormant pruning and destroyed as it serves as an important
inoculum source. Wood infected with phomopsis has been shown to produce spores
over a period of several years.
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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All images © Texas A&M AgriLife