Agriculture Reference
In-Depth Information
Good prevention is important to help deal with downy mildew. Plant resistant varieties.
Prune and train vines to encourage plenty of air circulation. Clean up debris between the
rows and control weeds.
As with other fungal diseases, treatment for downy mildew should start before bloom
and continue for a month after bloom, at weekly or biweekly intervals. Copper is the
primary fungicide for treating downy mildew, including copper sulfate, Bordeaux mixture,
and commercial organic preparations containing copper.
Eutypa Dieback
Eutypa lata
In spring, growing shoots show signs of the disease. Leaves may be small, stunted, and
yellow. You may notice these symptoms for a few years until the vine actually starts to die
back. But eutypa usually starts around old pruning wounds, forming a canker on the trunk.
If you pull away the bark over the canker, you'll see a flattened, dark area up to 3 feet long.
By the time you see this kind of damage to the trunk, the disease has progressed.
CONTROL
If you notice shoots that show eutypa damage, identify and remove infected vines. All
wood should be removed and destroyed, as the fungus can continue to emerge from trunks.
Prune late in the dormant season so that pruning wounds heal quickly. There is no approved
organic treatment for eutypa dieback.
Phomopsis Cane and Leaf Spot
Phomopsis viticola
Cool weather and rainfall release overwintering phomopsis fungal spores from infected
wood. Black spots and lesions appear on the shoots. Although the fruit is infected when
young, it does not start to rot until later in the season. Close to harvest, the grapes might
turn a light brown color, spotted with black.
CONTROL
Copper fungicides are recommended for phomopsis. The critical period is when the clusters
are developing until up to a month after bloom.
