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Head scab

Considerations when planting wheat after corn

By Pierce Paul, Ohio State University Extension plant pathologist

Some Ohio wheat growers are thinking about planting wheat after corn to avoid some of the late planting issues we have had to deal with over the past few years. Indeed, timely planting will result in good stand establishment (more tillers per foot of row) and reduce the risk of winter kill. However, planting wheat after corn to ensure that the crop is planted early enough has disadvantages.

In wheat following corn, being both members of the grass family, both crops may be affected by some of the same pests and diseases. One such disease, and by far the one of greatest concern, is head scab, caused by Fusarium graminearum. This same fungus causes Gibberella ear and stalk rot in corn. Consequently, wheat planted into corn stubble is more likely to have head scab and vomitoxin problem next year, especially if late-spring, early-summer conditions are wet and humid. Our studies have shown that when host crop (corn, wheat or barley) residue is abundant (more spores of the fungus present), only a few days of wet and humid conditions during flowering are needed for head scab to develop and vomitoxin to exceed critical grain marketing thresholds (2 ppm).

With the high levels of Gibberella ear rot we are seeing in some fields this year, there will be plenty of spores around next spring, increasing the risk of head scab if conditions become wet and humid during flowering. This is exactly what happened in 2009-2010 — Gibberella ear rot in corn in 2009, followed by high levels of head scab, vomitoxin and grain rejection in wheat in 2010. Remember, one of the best ways of minimizing the risk of head scab and vomitoxin is to plant wheat after soybeans and not after corn. Let’s break the cycle of vomitoxin problems.

If you HAVE to plant wheat after corn or have already done so, hopefully you have planted a scab resistant variety or will do. Even when wheat is planted after soybean, planting a scab resistant variety is highly recommended. In addition, plow under the corn stubble before planting wheat and be prepared to apply a fungicide next year at flowering if the weather becomes favorable. These approaches will minimize, but not eliminate the risk of scab in wheat planted after corn.

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