How to Manage Pests

Pests in Gardens and Landscapes

Common smut of corn—Ustilago maydis

Common smut is easily recognized by the tumorlike galls that form on any aboveground plant part. Galls at first are a glistening, greenish white to silvery white. Galls on ears and stems expand and fill with masses of powdery, dark olive brown to black spores. Galls on leaves and tassels remain small and become hard and dry. Ear and stem galls rupture, and wind, rain, or irrigation water spread them through the garden.

Identification

Head smut may be confused with common smut. However, the vascular bundles within the galls of head smut readily differentiate head smut from common smut. In head smut, leaflike proliferations often occur in tassels and partially smutted ears.

Life cycle

Spores overwinter in the soil. Under favorable conditions they form secondary spores that are carried by air currents or splashed by water to young, developing corn tissues. Development of common smut is favored by dry conditions and temperatures between 78 and 93°F. The incidence of smut is higher in soils high in nitrogen or after heavy applications of manure. Injury to the plant tissue of any kind increases the potential for smut infection.

Solutions

Remove and destroy tumorlike growths as soon as noticed; keep the black powder in galls from getting into the soil. Plant early as common smut becomes more prevalent in later harvests. All corn varieties are susceptible to common smut to some degree. Try to plant varieties that are the least susceptible to the disease. Rotating out of corn for as long as possible can help reduce overwintering spores in the soil.

Common smut of corn
Common smut of corn


Statewide IPM Program, Agriculture and Natural Resources, University of California
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