Grape plants are susceptible to a variety of pests and diseases that may cause severe damage if left uncontrolled or untreated. Since herbicides have the potential to damage grape plants, understanding the particular pests and diseases that commonly affect grape plants, like black rot and the grape flea beetle, is key to maintaining vigorous plants.
Black rot is a disease of grape plants. Black rot develops due to the presence of the fungus Guignardia bidwellii. A disease with potential for severe injury, black rot affects leaves, shoots, tendrils and flowers, causing leaf drop and berry rot, according to the University of Tennessee Agricultural Extension Service. The fungal infection causes light-brown leaf spots that turn red-brown and develop a brown-black border. Within the leaf spots, the fungus forms small, black bumps. Black rot also appears as black lesions on stems, and spots on berries that grow larger and cause the fruit to rot--berries shrivel and fall from the grape plant. For control, make sure vines are well-spaced, soil has good drainage, plants are in full sunlight and the grape plant is kept pruned. Also, apply an early-season fungicidal spray.
Downy mildew is a problematic disease of the grape plant. The fungus Plasmopara viticola develops into an infection within the grape plant. Downy mildew affects the entire vine, causing leaves to turn yellow-green and lesions that look oily to appear on leaf surfaces. Beneath leaves, gray, cotton-like formations develop, and leaves curl and drop. On shoots and tendrils, white mildew forms in slick depressions, and plant parts become brown in color and die. Infected fruit becomes light-brown in color, softens, and the downy mildew appears during humid weather, according to the University of Illinois Extension. For control of downy mildew, follow the same methods as suggested for black rot but apply fungicide when shoots are 1/2 inch in length, just before and after bloom.
Grape Flea Beetle
The grape flea beetle is a pest of grape plants, according to the University of Kentucky Agricultural Extension. Larval stage grape flea beetles devour flowers and leaf tissue, while the adults consume buds and leaves. Larvae are brown in color with black spots; adult grape flea beetles are green-blue, with a metallic sheen, and measure approximately 1/5 inch in length. For control, grape flea beetle pesticide spray is effective. Consult a professional to determine the appropriate spray for your region.
Grape Root Borer
Considered a highly devastating pest of grape plants, according to the University of Kentucky Agricultural Extension, grape root borers can demolish an entire root system. These grape plant pests attack in larval and adult stage. Larval borers take on a cylindrical shape with a cream colored hue and measure 1 1/2 inches in length. Adult borers are moths displaying a brown color and a narrow, yellow stripe on their bodies. The larvae search out the roots of the grape plant by digging into soil and feeding for a duration of two years. Mature, adult borers exit the soil during the middle of the summer season. For control, the University of Kentucky Agricultural Extension suggests spraying insecticide within 15 square feet of the grape plant if a problem is apparent.