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College of Food, Agricultural, and Environmental Sciences

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August 17, 2021 - 8:00am -- lehman.488@osu.edu

The other day I was walking a corn field and a couple of ears caught my eye. Large silvery and smooth blobs, for a lack of a better word, had taken over the top half of the ear. This was none other than common smut. Common smut is one of three smuts that can affect corn; the other two are head smut and false smut. All three smuts are caused by different species of fungus and are outlined below.

Common Smut

This smut is also known as blister smut or boil smut and is caused by the fungus Ustilago maydis. This affliction is quite dramatic in appearance, as I mentioned earlier. Essentially, masses of silvery tissue, called galls, replace kernels on the ear of corn. Galls can also develop on other parts of the plant such as on the stalk and on the leaves. As these galls mature, the interior becomes dark and filled with spores.

 As terrible as this disease looks, especially when on the ears, I was surprised to find out that it rarely affects yield in field corn unless the issue is intense and widespread. When common smut does take a large hold of the crop, it also reduces corn quality for processing but does not pose a threat to livestock as other fungi are known to do. This disease mainly affects sweetcorn cultivars, and luckily for some, there is a market for galled ears. Dating back to the Aztec era, fried corn smut galls have become a delicacy, dubbing them “Mexican truffles.”

Management of common smut involves crop rotation or planting in a smut-free location as the spores survive in soil for several years. Splashed water, plant stress, or excessive nitrogen application have all been associated with increased smut incidence. Unfortunately, treated seeds or foliar fungicide application does not reduce the incidence of common smut.

Head Smut

Head smut is caused by Sphacelotheca reilana which has two strains: one attacks corn and the other attacks sorghum and Sudan grass. While it is far less common than common smut in Ohio, it has been reported. Typically, it shows up in the drier Plains states. This smut can be identified by round galls on the ear, almost looking as if it replaces the cob and kernels in total. Dark, powdery spores will erupt from the burst gall. Thin strands also emerge from the gall, which is the disease’s defining characteristic, and are actually the remaining portions of the corn vasculature. The plant may also produce many more tassels than an unaffected plant and if the tassels are infected themselves, may be spikey in appearance.

Again, like common smut, this disease is more likely to affect sweet corn and popcorn rather than field corn. The spores will live in the soil and practicing a 3-year rotation will aid in keeping the fungus at bay. The spores also survive well in acidic soils. The University of Oregon suggests using seed treated with carboxin as a preventative or limiting measure.

False Smut

The last smut to talk about is false smut caused by Ustilaginoidea virens, which typically impacts rice. It is called false smut because it does not release spores from spongey galls like other smuts, but instead packages them in a little sac. False smut of corn is only reported a few times in the United States, the major one occurring in the Mississippi Delta in 2000 but was not observed the following years. No economic losses were reported because only the tassel was affected. Therefore, false smut is of extremely little concern in Ohio.

Fungal infections in corn take many different shapes, but ultimately, common smut is the most likely of the three you’ll encounter in your fields. Unfortunately, fungicides are not an appropriate method in which to control current smut outbreaks, but rotating crops can help limit the disease in the following years. Additionally, selecting less-susceptible cultivars can also enhance yield, especially if you are a sweetcorn grower.

Please join Wayne County Extension at a Small Grain and Cover Crop Field Day on August 26 from 10 AM to 2 PM at the OARDC Land Laboratory. We will be discussing wheat trials and grazing practices. Cost is $10 per person for lunch. Visit go.osu.edu/waynefieldday or call 330-264-8722 to register.

 

Haley Zynda is an OSU Extension Agriculture & Natural Resources Educator and may be reached at 330-264-8722.

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