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Vomitoxin on Wheat

The 2014-2015 wheat crop has certainly had its share of problems this season. Much of the crop was planted later than normal and this spring we had more freeze/thaw cycles than we have had in several years. We also experienced extremely wet conditions in May and June. We are now seeing a delayed harvest with sprouting heads, lower test weight, and vomitoxin.

Vomitoxin, or DON (Deoxynivalenol) is usually produced on wheat and barley heads that were infected with Fusarium head blight, or scab. Just because you have scab does not mean that you automatically have DON. In fact, we have experienced many years of scab without vomitoxin. DON can also occur in fields that have a delayed harvest but don’t have much scab, which I believe is the reason we are seeing more of it this year.

According to the Compendium of Wheat Diseases and Pests Third Edition, “In general, Fusarium will only grow in wheat in which grain moisture is in equilibrium with relative humidity above 90% (20% to 25% grain moisture). These fungi can grow at temperatures from near 0 to 30 degrees C. (32 to 86 degrees F.) with optimal growth of most species occurring around 25 degrees C. (77 degrees F.)." In other words, we have had great environmental conditions with all the rainfall maintaining high humidity, moderate temperatures, and delayed harvest for fostering a lot of vomitoxin.

Growers who used a fungicide such as Prosaro®, Proline®, or Caramba® at flowering saw healthier wheat and less vomitoxin, although they have still seen sprouting, lower test weights, and some scab. A fungicide for head scab is effective when ideally timed, although you are never going to get 100% control of scab due to wheat flowering over a long period (approximately 10 days). Strobilurin fungicides, such as Quadris® or Headline®, applied at flowering, have shown to actually increase DON levels. Varieties will also differ in their susceptibility to scab.

For those who may be thinking about saving seed for wheat this year (which we don’t recommend since it is illegal because most wheat has variety patents), scabby wheat with low test weight will give poor stands, and seed treatments won't offer much relief. Seed companies have ways of dealing with scabby wheat to improve quality: This includes recommendations to growers to help prevent infection to begin with, cleaning practices, and gravity tables.

Getting the wheat harvested as soon as possible and dried down to the proper moisture should stop the fungus and DON levels from continuing to grow. Now, if we could only stop the rain to make that possible!

Alex Johnson | Field Agronomist

For more Agronomic News from Alex Johnson, certified crop adviser, please visit his Agronomy Page on

Prosaro®, Proline®, Carabma®, and Headline® are registered trademarks of Bayer CropScience

Quadris® is a registered trademark of a Syngenta Group Company

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