This fungal disease occurs sporadically in sweet corn as well as field corn. It has not been significantly impacting yield of fresh market sweet corn. Common smut can reduce yield and create difficulty in handling for processing corn. In some countries, including Mexico, corn affected by smut is consumed before the galls erupt and thus is cultivated.
Causal agent: Ustilago maydis
Plant parts affected: Leaves, ears, stems, and tassels call all be affected. Seedlings can be infected, but this occurs rarely.
Favorable conditions: Rain and humid weather are favorable for initial infection; dry, sunny weather and high N levels for disease development.
Symptoms: Symptoms on ears are most distinctive. Corn kernels are replaced by large, fleshy galls covered by silvery-white membrane that rupture exposing black mass of spores. Small bumps on leaves are the first symptom, developing in the leaf whorl stage. Symptoms on stems and tassels are like those on ears.
Survival and spread: Spores survive associated with debris in soil and are dispersed by wind. The spores lodge in nodes and growing tips.
Control: Choose resistant varieties. Select a field where sweet or field corn was not grown the previous year. While crop rotation is recommended, considering the pathogen produces windblown spores from debris, proximity of fields where common smut occurred the previous year will impact smut occurrence in the crop. Steady growth of corn reduces amount of smut. Excess nitrogen and mechanical injuries increase prevalence. There are no fungicides. Destroy crop debris promptly after harvest to hasten decomposition.
Following images of common smut affecting leaves, tassel, stalk, and ears of corn were taken on Long Island.
