Common smut of corn is caused by the fungus Ustilago maydis. The fungus causes gall formation on all aboveground parts of corn plants. In some parts of the world, such as Mexico, immature galls are eaten and considered a delicacy. In the United States, infected ears are usually culled.
Galls are most obvious on the ears (Fig. 1), but they may also form on leaves, tassels, and stalks. The galls are at first enclosed in a silvery white membrane. As they mature, the membrane breaks and a black, powdery mass of spores is exposed. Smut on the leaves and tassels usually appears as very small galls or pustules (generally less than an inch in diameter) that eventually become hard and dry. On all other parts of the corn plant the galls are frequently several inches in diameter. Ears are most often infected at the tips, but they may be invaded at any other point. The entire ear is sometimes replaced by the smut gall, which is usually partially or wholly enclosed by the outer corn husk. If plants become severely diseased before they are a foot high, they are usually either killed or stunted in growth.
The factors that determine severity of common smut are not fully understood. Hot, dry weather during pollination, followed by rainy weather, seems to favor disease spread and development. Corn grown on heavily manured soils often develops severe smut. Plants on such soil produce succulent growth, which may be more susceptible to fungal infection. Such soils may also provide a good medium for the overwintering and germination of the smut spores.
Table 1. Sweet corn varieties with some resistance to common smut
White Sugary Enhancers
Seneca Snow Prince
Seneca Sugar Prince
Summer Flavor 72W
Table 2. Sweet corn varieties that are highly susceptible to common smut
Country Gentlemen Hybrid
Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products which also may be suitable.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Interim Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 1, 2009