The Brown Rot and Black Rot Plant Diseases

Most gardeners who have grown apricots, peaches, plums or cherries are familiar with the brown rot and black rot disease. Brown rot may attack blossoms or shoots, but it is most disheartening when it attacks the ripening fruit. Fruit decay is rapid on ripe fruit and slightly slower on immature fruit. At first, brown rot appears as small, circular, light-brown spots on the surface of the fruit. Under favorable conditions, the spots expand rapidly. Under wet, humid conditions, ash grey tufts of fungus growth develop over the surface of the lesions. Rotted fruits may fall to the ground or persist as mummies on the trees.

Both cleanliness and fungicides are necessary to control this destructive disease. Brown rot fungi overwinter in mummified fruit on the three or on the ground as well as in twig cankers. Mummified fruit should not be allowed to remain on the tree nor on the surface of the soil near trees. As soon as it is seen, diseased fruit should be picked, destroyed or buried so the fungus is not able to continue to produce spores that are spread throughout the tree by wind.

The spores may also be spread short distances by splashing drops of' rain. If the area beneath trees is too large to clean up in any other way, shallow cultivation to turn under any mummified fruit may be helpful. This should be done before bloom time. As with many other diseases and pests, control throughout the season is most effective. However, to control brown rot on ripening fruit, pre-harvest sprays should be begun three weeks before harvest.

The more severe the infection, the more frequent the spray intervals need to be to bring the problem under control. Normally, two applications of benomyl (Benlate) during this time period are adequate. Frequent rains may mean an extra application. This material may be used up to the day of harvest. Black rot is a different fungus disease, but its effect on grapes is similar to that of brown rot on the stone fruits. Infection may occur on leaves or young canes, but it is in the fruit where it is most noticeable.

Although other diseases may attack grapes as they ripen, black rot most often infects them while they are still green. It first appears as light-brown, circular spots that enlarge rapidly until they cover the entire berry in two or three days. Small black specks begin to appear on the rotten berry. Within a week to 10 days, the grape berry is transformed into a black, hard, shriveled mummy, which may remain on the bunch. Some drop may occur while the berries are rotting.

Cleanliness is also quite important to prevent carry-over for another season. The disease overwinters in mummified fruit as well as in fallen leaves. A fungicide spray during the growing season helps prevent buildup of the disease. It is particularly troublesome during season with warm, moist weather when new shoots become infected. The same material used for brown rot in peaches may also be used for control of black rot in grapes.

The first application of benomyl should be made three to four weeks before harvest with an additional application about two weeks later. Do not apply benomyl within days of harvest on grapes. In some cases it may be too late for adequate treatment this season. However, if the problem exists, remember to destroy diseased fruits and start control early next year.

Sources:

http://en.wikipedia.org/wiki/Black_rot
http://en.wikipedia.org/wiki/Brown_rot