Grape vines are primarily grown for the fruit crops they yield. Protecting these crops from grape vine diseases is imperative for the highest grape yield and most profit. Learning the various types of grape vine diseases enables growers to correct problems and thus save crops.
Black Rot Disease
During the mid-summer months, black rot disease can appear on some varieties of grape vines. The fungus Guignardia Bidwellii causes reddish-brown spots to appear on the vine leaves. Later, black rings surround the damaged area with black dots in the center. Grapes shrivel, dry out and fall off the vines.
Applying the herbicide Gramoxone to grape crops on a regular schedule is the best prevention from Black Rot Disease. According to MSU Extension, Concord, Niagara and Aurore grape vine varieties are most vulnerable to black rot disease.
Downy Mildew Disease
The fungus Plasmopara Viticola causes downy mildew disease on grapevine plants. Spores spread the fungus to grapevine leaves from the ground, particularly after rains or in wet or high-dew growing regions. Downy mildew appears as a white fungus. Later, this turns to yellow circular spots on the leaves. Infected leaves fall off the vines and expose grapes to direct sun. This results in grapes burning from heat and too much sunlight.
Since downy mildew disease spreads from the spores, entire crops are often destroyed by this disease. According to MSU Extension, the use of multiple fungicides can control and prevent downy mildew disease on grapevine crops. Several applications during different phases of blooming improve the odds of reducing or preventing the disease's spread.
Crown Gall Infection
The bacteria Agrobacterium Tumefaciens causes crown gall infection in grapevine plants. Crown gall enters vineyards by two common methods. One method is through infected grapevine shipments. The other is through bacteria-infected pruning shears. Crown gall attacks the grapevine roots and leaves small gall, or swollen tissue, areas.
One significant problem with the bacteria that causes crown gall is its high survival rate in vineyard soils. Agrobacterium Tumefaciens can survive for several years once it infects the soil of growing areas.
According to MSU Extension, it is imperative to disinfect equipment during grape vine pruning. The organization recommends dipping roots in a substance that makes grapevines resistant to the bacteria that might be already present in growing soils.