SMUT IN THE CORN FIELD

Smut is one of those words that evokes a myriad of thoughts: a corn fungus, a highly valued food delicacy, those elusive magazines displayed behind the convenience store counter.

Because I’m not looking for early retirement, we’ll leave deliberation on that third thought for another writer; however, smut as a valued part of the balanced diet is worthy of some discussion before addressing the agronomics.

30-huitlacoche-01Putting corn smut next to the mashed potatoes on the dinner plate is apparently common in Mexico. Of course it’s all about marketing so the name corn smut is replaced with the more exotic sounding huitlacoche (weet-la-KO-chee) or Mexican truffle. Stateside corn farmers have other names for this unique edible fungus as well.

My extensive research on this topic found that several higher end U.S. restaurants include corn smut on their menus. If you’re not up for an East or West Coast eatery excursion, it can be ordered over the Internet and delivered to your door for $1-$2 per ounce.

The canned smut…I mean huitlacoche…is considerably cheaper than the fresh frozen preparation. One vendor describes it as being “similar to mushrooms in texture and flavor, with an earthy, somewhat smoky taste.” Focus on the earthy.

The ancient Mayans and Aztecs, who reportedly had a hand in starting this culinary tradition, called corn smut the “excrement of the gods.” Focus on the excrement.

It is worthy to note on Amazon.com that people who ordered huitlacoche also were interested in blindfolds, freestyle motocross, and Fear Factor: the first season DVD. I highly recommend several YouTube educational videos for the smut connoisseur.

Enough about the fine dining aspects of corn smut; this is an agronomic column and 2012 resulted in more than the usual amount of smut in Wisconsin corn fields…the disease, that is.

The corn smut fungus, Ustilago maydis, produces spores that survive in the soil or on crop residue for several years. When given a mechanism to enter the corn plant under favorable environmental conditions, the ear infection results in the growth of a large gray and black fungal mass.

Sweet corn hybrids are more susceptible than field corn hybrids, but infections in field corn are still common given the right set of conditions.

The unusual thing about 2012 is that this was a dry year. Often we see high corn smut occurrence in years with extended field flooding early in the growing season. In this case, the spores are transported by water onto and into the plant.

CornSmutIn 2012, our extended dry soil conditions likely allowed for spores to be spread, along with dust, onto plants by wind and field traffic. Infections can take place through plant wounds caused by insects, hail, or mechanical damage. They also can occur through the silks, especially when pollination is poor as was the case in many 2012 fields. Moisture and high humidity favor infection.

After infection, the fungus causes plant cells to rapidly divide and expand, resulting in the characteristic large gray galls that fill with black spores. These spores are eventually spewed-out over the plant tissues and soil. Upon seeing these galls at harvest, many farmers also spew-out a variety of choice words.

Fortunately, corn smut rarely causes significant yield reductions in field corn. Like an aging tattoo, it looks worse than it really is. In cases where corn smut does cause yield reductions, it’s usually the result of some other event: for example, a severe hail storm.

Often the question is asked whether or not corn smut impacts animal health or feed palatability when the crop is chopped for silage. Common corn smut doesn’t produce any toxins as some other corn molds are known to do. Most feeding trials show no impact on animal health or palatability. Under extreme cases of greater than 50 percent infection, some trials indicate feed digestibility is reduced, but this level of infection would be rare in the northern U.S.

There is little a producer can do to control corn smut other than to plant hybrids with good genetic resistance. Some evidence exists that links higher fungal infection levels with excessive nitrogen fertility. Crop rotation has also proven beneficial as is the case for many plant disease issues. There are no seed or foliar fungicides that control the disease.

Corn fields with higher than normal smut infestations in 2012 are probably of little consequence. If, however, you go to the in-laws and find a gooey black mass sitting next to your pot roast…that’s a concern.

Mike Rankin, Crops and Soils Agent, UW Extension-Fond du Lac County

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