By Jennifer Olvera, Garden Guides Contributor

About Black Rot

Black rot is a fungal disease that causes darkening and decay on the leaves of fruits and vegetables,especially during hot, humid conditions. It primarily affects above-ground portions of plants and can occur at any stage of growth, causing major loss of yield. The bacteria can over-winter in plant debris as well as in and on seeds from affected plants and weeds.

Prevention and Control

Early on during the greenhouse stage and in the field, remove problem foliage. Cruciferous weeds are a common source of contamination and should be removed from the planting area. Dispose of potentially affected debris.

Affected Plants

Grape vines, cranberries, apples and vegetables and weeds in the crucifer family, among others.

Damage

Spots can be small and large, superficial and deep, and are not always black. Black rot destroys crops. The spots often start as yellowish, irregular, circular areas and later become grayish brown and finally black. They can appear as yellowish marks,and later black or brown V- or U-shaped lesions along leaves. The spots may drip with a gummy substance in the center.

Causes
Black rot is a bacteria-driven disease that flourishes in humid, rainy conditions.

Predator Insects

There are no predator insects, however insects can spread black rot and infect healthy plants, exacerbating the problem.

Natural Insecticides

Champion (copper hydroxide) plus lime, GC-3 (a blend of cottonseed, corn oil and garlic extract), Serenade (Bacillus subtilis) and Armicarb O (organic formulation of potassium bicarbonate) can help control and eliminate black rot.

Other Methods of Control

Treat seeds with hot water before planting to eliminate potential bacteria. Crops should be alternated between cruciferous and unrelated crops every 3 years, since plants such as tomatoes, peppers and cucumbers are not susceptible to black rot. Clean all greenhouse material, machinery and irrigation tools. Use sprinkler irrigation in moderation.