Gail Ruhl, Senior Plant Disease
Diagnostician, Department of Botany & Plant Pathology, Purdue
Black rot is a bacterial disease of Crucifers.
Foliar symptoms may vary depending on the specific Brassica host,
age of host when infected and environmental conditions. Initial
symptoms usually consist of small water-soaked leaf spots. As
time progresses, more
characteristic and recognizable symptoms are those of angular or
V-shaped yellow lesions that often develop along the leaf edges
and eventually dry up and turn a tannish to brown color.
The source of this bacterial pathogen may be
from infected seed, diseased weeds and volunteer crucifers and
infested, not yet decomposed crop residues.
Controls recommended in "Vegetable Diseases--A Color Handbook" by
Koike, Gladders and Paulus include the following:
1. Use seed without significant levels of the pathogen.
2. Be sure all infected crop residue decomposes before re-planting
susceptible Brassica hosts back in the site. Once crop residues
are gone, the bacterium does not survive in the soil.
3. Use resistant cultivars, if available.
4. The application of chemicals to foliage is not very effective
for black rot control.
Diseases: A Color Handbook Order Form (pdf file)
Photos courtesy of Steve Mayer, Marion County
Extension Educator, Purdue