How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

On cole crops, Rhizoctonia causes two types of disease symptoms: damping off (or wirestem) and bottom rot.

Damping off or wirestem occurs on newly emerged or very young transplants when Rhizoctonia attacks the hypocotyl or lower stem tissue in contact with the soil. This results in browning and cracking of the epidermis and the formation of lesions. As infection progresses, the outer stem decays, leaving only the fibrous inner xylem intact (hence the name wirestem). Affected plants wilt, turn purple, and remain stunted. Seedlings may break off at the soil line. The pathogen can usually be identified by its coarse mycelia that often causes soil particles to adhere to and dangle from diseased stems.

Bottom rot is primarily a problem on cabbage, bok choy, and Chinese cabbage. Once head formation begins, lower leaves in contact with the soil may become infected with Rhizoctonia. Dark brown, oval lesions develop where soil touches the leaves. Secondary decay organisms may follow and make these lesions soft and watery. Infected leaves may wilt, exposing the head. Occasionally the pathogen may grow up into the inner tissues of the cabbage head.

COMMENTS ON THE DISEASE

Rhizoctonia solani is a common soil inhabitant that survives for long periods in soil on crop residue or as sclerotia. Wet, warm soils favor wirestem development. Seedling susceptibility decreases as plants mature.

MANAGEMENT

Prepare good quality seedbeds before planting. If possible, plant when soils are warm because seeds germinate faster and seedlings are more vigorous. Avoid excessively wet soils during early stages of seedling growth. If transplants are used, do not plant too deep if Rhizoctonia diseases are a problem in the field. No other control measures are recommended.

PUBLICATION

UC IPM Pest Management Guidelines: Cole Crops
UC ANR Publication 3442
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
K. V. Subbarao, Plant Pathology,UC Davis, Salinas

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