Wednesday, April 11, 2012

The Current Wheat Crop and Risk for Head Scab

Chad Lee, Extension Agronomist, University of Kentucky

Weather in some parts of Kentucky dipped below 30 degrees Fahrenheit last night (April 10 into this morning April 11). These temperatures are low enough to damage wheat that is heading. About 10 days of good growing conditions are needed to assess damage to the wheat crop. Some of the wheat is flowering and farmers need to make decisions now on spraying the wheat with a fungicide. Should they spray these fields?

The following is a synopsis of a conversation with Don Hershman, extension plant pathologist.

Across Kentucky, the head scab (Fusarium head blight, FHB) risk is barely registering in the models due to the greatly unfavorable environment in recent weeks for spore production. In other words, it is very likely that the main effect of any rain in the near future would be to rekindle the spore production process in the residue, but according to the models, it will take at least 7 days for spores production to reach a critical mass. Right now there simply are not enough spores around to infect wheat. So, unless we really get socked in with warm, wet weather, the risk of FHB should stay low for at least the next week. Most fungicides have a 30-day to harvest restriction, so that is the main aspect of the label that determines how late fungicides can be legally applied.

 In the end, there is some risk of treating or not treating. I am not a betting man, but if I were, I would say that the odds are pretty good that the FHB risk will stay reasonably low throughout the critical time of flowering for most fields. Once the crop has flowered, there is still a risk that DON contamination might be a problem in grain if conditions are wet during grain fill. But fungicides would not be expected to alter that situation much one way or the other.

Bottom line: I think your main concern at this time is potential freeze damage and not FHB. Still, some of you might opt to spray treated crops to protect against FHB/DON and other diseases should weather conditions in the near term turn highly favorable for disease development. Others might opt not to spray a fungicide considering what I have said above, as well as the numerous unknowns surrounding the extent of freeze damage. I would not argue with either approach.

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