Corn smut: A blessing or a curse?

Corn smut grows on an ear of corn. Wikipedia

Dear Aggie:

Several ears of my sweet corn were ruined by what look like large gray tumors. What is this and how can I prevent it?

Depending on who you ask, corn smut is either a blessing or a curse.

Corn smut or Devil’s Corn (Ustilago maydis) is a common fungal disease that infects corn in the early stages of development. Sweet corn is more susceptible than dent or field corn. The fungal spores travel on the wind and can disperse over long distances, particularly during dry and hot weather. Spores land on and then infect plant tissues. Infection occurs most easily when there is water present on the surface of the plant or at injury sites due to mechanical damage. As the disease progresses, large white to grey galls appear. The galls are particularly noticeable on ears and tassels; each kernel of corn can become a single large gall when infected. As the galls age, the interiors turn an inky black before finally erupting. Spores are then released into the air, repeating the cycle of infection.

The disease is most common in fields with high nitrogen levels, particularly those that have received heavy applications of manure. During mechanical harvesting of field corn, the galls will open and spread spores throughout healthy kernels of corn and fodder. Both are fed to cattle. Because spores can pass unharmed through cattle’s digestive tracts, the disease cycle continues when manure is spread back onto corn fields.

There is a little that gardeners can do to stop the disease. Seed treatment is of no value and most control measures (fungicides) are unsatisfactory and expensive. While some varieties are more resistant, no variety of corn is immune. For example, Silver Queen is highly susceptible while Silver King is more resistant. The use of drip irrigation in corn will minimize water sitting on leaves, but the disease readily infects plants through morning dew. Removing infected corn stalks before the spores erupt would help only if all gardeners and farmers did the same. Given that most of us have corn fields within a few miles of our garden, the disease will reappear whenever conditions are ripe.

A select few gardeners, including me, welcome the appearance of corn smut – otherwise known as Huitlacoche or Mexican Truffle. The galls of corn smut are entirely edible and quite delicious. The galls should be collected while they are still firm and before the spores erupt. The fruiting bodies have a flavor reminiscent of truffles or wild mushrooms mixed with the sweet and delicate taste of corn. The fungus is particularly prized in Mexico and larger cities where produce vendors sell the fresh product for a premium. Because it has an extremely short shelf life of only a day or two, huitlacoche is commonly sold canned or frozen. An 8-ounce jar can sell for as high as $9.00 while a pound of the fresh fungus can go for up to $35.00! Huitlacoche can be lightly sauteed, often with garlic and onion, for use as a taco or quesadilla filling. Some chefs use it as a pizza topping or to fill ravioli. Notably, huitlacoche is packed with unsaturated fatty acids, protein, and all essential amino acids.

Gardeners wishing to promote huitlacoche in their garden might have as much luck than those trying to prevent it. Cultivation practices are still largely under development. The University of Wisconsin-Madison has researched methods to promote growth of the galls using artificial inoculation with mixed success. When corn begins to tassel, a water solution containing spores are sprayed onto or injected into the corn silk. When successful, galls form within two weeks. Early harvest is essential to maximize shelf-life.

What’s the lesson in all of this? If life gives you corn smut, make tacos.

Question answered by Mike Nuckols, Ag Team Leader, msn62@cornell.edu.

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