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.
