AVRDC International Cooperators'
Fact Sheet

Crucifer Diseases
 

Rhizoctonia
Rhizoctonia solani

Found worldwide

Damage Symptoms

The pathogen can attack most crucifer plants at any stage of development. When young seedlings are attacked and killed before or soon after emergence, the disease is referred to as damping-off. When stems of older seedlings are attacked, the plants usually survive, but the cortical tissues are damaged causing the disease known as wirestem. During warm wet conditions, the fungal mycelium grows over the leaf surfaces matting them together and causing large irregular-shaped lesions that later dry and fall out; this phase is called web blight. Lower leaves in contact with soil develop large water-soaked lesions and this phase is known as bottom rot. Frequently, infection from the lower leaves progresses into the head of cabbage causing it to decay; this phase of the disease is known as head rot.

Extensively damaged foliage of mustard

Conditions for Development

The fungus can survive in crop debris indefinitely. It also produces sclerotia that can survive in the soil during unfavorable conditions. Disease may develop over a wide range of conditions when susceptible hosts and the fungus come into contact.


Control

To reduce damage from damping-off and wirestem, a pasteurized soil medium is recommended for growing transplants. If seedbeds are used, they should be disinfested by fumigation when feasible. If disease develops, the beds should be drenched with a recommended fungicide. The use of fungicides in transplant water may minimize the wirestem phase of the disease. Bottom rot and head rot disease losses can be minimized by allowing sufficient time for green manure to decompose before planting, and by preventing soil from being thrown onto the plants during cultivation.

Last updated: 2001. 
Information from: Vegetable Diseases: A Practical Guide. Lowell L. Black, AVRDC.

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