Black rot of grape

About

One of the most serious grape diseases in the eastern United States, able to destroy anywhere from 5 to 80 percent of a crop. It turns berries into hard, black, shriveled mummies.

Also called black rot, grape black rot

How to recognize it

Symptoms

Leaves get reddish-brown round spots whose centers turn brown, ringed with tiny black specks. Infected berries turn brown, then shrivel into hard black mummies covered with black dots. Fruit are hit hardest from about pea size on.

Worse when

Warm, wet weather; at 60 to 80°F only 6 to 9 hours of leaf wetness is needed, and shady, crowded vines stay wet longer.

How it spreads

The fungus spends the winter in mummies on the ground or left hanging in the trellis and in cane lesions; spring rains splash and blow spores onto new growth.

When

From early shoot growth through about 3 to 4 weeks after bloom, when berries become resistant; few new infections occur after late July.

Where

Worst in the humid eastern United States.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Clean up mummies before growth starts Prevent

   During the dormant season, pull every mummy and dead tendril off the trellis, prune out infected canes and remove or bury mummies on the ground.

   All cultivated grape varieties can be infected, and mummies left in the trellis keep releasing spores all season.

2. Give vines sun and air Prevent

   Grow grapes in a sunny, open spot and train and prune so the canopy dries quickly.

3. Pick off the first spotted leaves By hand

   If only a few leaf spots appear in spring, remove those leaves.

4. Mancozeb or myclobutanil Conventional spray

   Start when new shoots are 3 to 5 inches long and repeat every 7 to 10 days through 3 to 4 weeks after bloom; the stretch from just before bloom to 4 weeks after is the most important.

   Sulfur, copper and oils do not control black rot, and captan is only slightly to moderately effective. Mancozeb cannot be used within 66 days of harvest on grapes. Follow the label.

Plants it affects

Grape