Tuesday, May 7, 2013

Current Head Scab (FHB) Risk Situation

Don Hershman, Extension Plant Pathologist, University of Kentucky

Below (in italics) is my current commentary off the FHB PREDICTION TOOL WEBSITE (www.wheatscab.psu.edu/).  The models on which the FHB risk assessments are based are considering spore production – not infection. So the models are basically saying that right now few Fusarium spores are being produced and if you don’t have the spores, you won’t have infection even if the conditions are right (which they are not).

Based on the map model, all of KY is currently at low risk (indicated as green). However, if you look at the other model in operation (click on a weather station {be sure to click on the red "Agnet" tab to see many more weather stations}), you will see that some areas are on the bubble (click on "probability" once you have clicked on a specific weather station), but the risk is still low for now. This status can change fast considering there is quite a bit of moisture in the soil. So if I were a farmer and had a good crop I would probably spray once my crop hit early flowering. I say this because other diseases will likely build up over the next month and you will also control any head scab infection that does occur.  Kind of a insurance approach knowing that the moisture levels will likely result in some disease over the next month.  But if FHB was the only consideration, the FHB risk is low for now.

If warm, wet conditions set in during grain fill, FHB and especially DON contamination of grain, can still be a problem.  Note: fungicides used to manage FHB/DON have very limited movement in the head following application. Systemic movement in leaves is much more substantial. As a result, if heads have emerged, but flowering is not underway, FHB control will be compromised if you spray a fungicide. You must wait to spray until flowering begins (as indicated by the presence of anthers) or up to 6 days past the onset of flowering, to get respectable FHB/DON control.Treating prior to the onset of flowering is only appropriate if some other disease, such as stripe rust, is developing and waiting would result in that disease getting out of control.

“Wheat is now flowering throughout most of west Kentucky, which is the main target for spraying fungicides for FHB control. It has rained all weekend and the FHB risk is still low in KY. Many people are contacting me asking why. I believe it is the cool weather. We have had this before where warm, dry days are mixed in with wet, cool days during the critical 7-consecutive-day window the FHB predictive models use. My experience has been that the models are very accurate when we have a mix of dry/warm - wet/cool days. Just keep watching for updates, but I do believe the models are accurate. The FHB risk could increase very fast, so spraying a decent crop asap might still be in order. Research shows that fungicides applied up to 6 days after the onset of flowering still work well. So if your crop is flowering now and it is not possible to spray, all is not lost. This is especially true considering the low FHB risk right now. I am confident that infection IS NOT taking place at this time.”

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