Starlings, robins, finches, grackles, mockingbirds, and blackbirds like the sweetness of ripe grapes. Entire bunches of grapes may disappear within a few hours. Birds are hearty eaters and, if not discouraged from the vineyard, may devour all the grapes in a planting. The sugar level in grapes increases during the ripening process. As the grapes approach maturity, birds keep a watchful eye on their progress. Birds seem to be more attracted to wine or vinifera grapes than to American bunch grapes. Early-ripening varieties and those with red or black fruit are most often attacked. When hungry, however, birds are not choosy.
To protect ripening grapes, loosely tie a paper bag or piece of cheesecloth over each cluster as it begins to ripen. Do not use plastic bags, because moisture will build up inside. Pick grapes promptly as they ripen. Bird netting placed over the plants and secured at the base with rocks or logs also protects the bunches. Nets are available at garden centers.
This plant disease is caused by a fungus (Guignardia bidwelli). It is the most destructive disease that attacks grapes, often destroying all of the fruit. The fungus spends winter in previously infected dormant canes, tendrils on support wires, and mummified fruit. In warm, moist spring weather, spores infect the new shoots, leaves, tendrils, and eventually the developing fruit. The fruit is affected in all stages of development but most severely when it is one-half to two-thirds grown. Spores for future infections are produced on infected leaves, canes, and fruit. The severity of the problem depends on how much diseased material survives the winter, and on the spring and early summer weather.
Destroy all infected fruit and prune out infected canes and tendrils. Once fruit has begun to shrivel, fungicide sprays are ineffective. The following year, apply a fungicide that''s labeled for black rot, following the label directions.
This plant disease is caused by a fungus (Plasmopara viticola) that attacks grape foliage and fruit from before bloom until the end of harvest. Downy mildew causes leaf defoliation and prevents proper ripening. When the disease is severe, entire clusters of grapes may be killed. Reduced vigor in the vines results in poor growth the following season. This disease is prevalent in cool, moist weather and is always more serious in rainy growing seasons. The fungus survives the winter in diseased leaves on the ground.
Destroy severely infected leaves and fruit. At the first sign of the disease, apply a fungicide labeled for downy mildew, following label instructions. Remove and destroy all plant debris at the end of the season to reduce the number of overwintering spores.
Endopiza viteana The grape berry moth is the most serious insect pest of grapes in the East. The larvae, or worms, damage both green and ripening fruit, feeding on the inner pulp and seeds. They spin webs with silken threads around the grapes and leaves as they feed. The worms spend the winter as pupae on leaves and on the ground, emerging as moths in late spring to lay eggs on blossom stems and small fruit. The larvae that hatch feed on the buds, blossoms, and fruit. After 3 to 4 weeks of feeding, they cut a small bit of leaf, fold it over, and make a cocoon inside, where they pupate. Within weeks, adult moths emerge to repeat the cycle, this time laying eggs on the ripening fruit. This second generation feeds for 3 to 4 weeks, then pupates over the winter.
Destroy infested grapes. Stop turning the soil in late summer; clean up cocoons remaining on top of the ground along with all fallen grape leaves at the end of the season. This reduces the number of overwintering pests. The following year, treat plants immediately after bloom with an insecticide labeled for grape berry moth, following label directions.
Treat infested plants with an insecticide labeled for grape flea beetle, following label directions. Give plants adequate food and water. Clean up garden debris thoroughly in the fall.
This common plant disease is caused by a -fungus (Uncinula necator) that thrives in both humid and dry weather. After it overwinters in buds or on canes, its growth is encouraged by warm days and cool nights. The powdery patches consist of fungal strands and spores that are spread by the wind to healthy leaves. The fungus saps plant nutrients, causing yellowing and sometimes the death of the leaf. Seriously affected leaves retard fruit ripening. The vine''s overall vigor may be reduced, resulting in poor wood maturity and increased susceptibility to winter damage. Fruit may also be attacked. Powdery mildew is a major problem in the West. Under favorable conditions, powdery mildew spreads rapidly through a closely spaced planting.
Treat infected grape plants with garden sulfur at the first sign of disease. Clean up and destroy debris around the plants at the end of the season. The next year, begin spraying the plants when the shoot growth is 4 to 6 inches long, and repeat at intervals of 2 weeks for four to six applications. Sulfur spray may burn leaves when temperatures are above 85°F.