P&PDL Picture of the Week for
October 1, 2007

Black Rot

Gail Ruhl, Senior Plant Disease Diagnostician, Department of Botany & Plant Pathology, Purdue University

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.

Vegetable Diseases: A Color Handbook Order Form (pdf file)

Photos courtesy of Steve Mayer, Marion County Extension Educator, Purdue University

Click image to enlarge

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service