Fusarium head blight (FHB) of wheat, and deoxynivalenol (DON) accumulation in harvested grain, are periodically very serious problems in Kentucky. There was minimal FHB or DON in 2006-2008 in Kentucky, but each year brings new possibilities. Thus, it is imperative that you be on guard for FHB/DON in 2009.

Since this time last year, several new fungicides have received Section 3 labels from EPA and can now be used to suppress both FHB and DON. Caramba (BASF), Prosaro and Proline (Bayer), and several tebuconazole products (e.g., Folicur, Bayer) can now be legally applied at early crop anthesis (flowering) for disease suppression. Previously, various propiconazole products (e.g., Tilt – Syngenta) were labeled for FHB control. The Regional Wheat Disease Committee, NCERA 208, has reviewed existing efficacy data and has concluded that Caramba, Prosaro and Proline provide "good" control of FHB and DON. Tebuconazole fungicides were given a "fair" rating, and propiconazole products were given a "poor" rating. Note: none of the products provide excellent control of either FHB or DON. Thus, it is still possible to take a serious yield and quality hit if FHB pressure is high this season. Fungicides are certainly not the silver bullet for FHB management. In fact, they do work best when applied to wheat varieties that have at least some resistance to FHB.

Excellent fungicide coverage on wheat heads is crucial to achieve the greatest possible FHB/DON suppression. This is no small challenge since most spray systems used in wheat were developed to deliver pesticides to foliage (horizontal structures). In order to maximize coverage on heads (vertical targets), significant changes may need to be made to the sprayer boom system. Also, discipline must be exercised to ensure that proper sprayer pressure and volumes are used.

Be sure to precisely follow all fungicide label instructions and restrictions.

Making Appropriate Fungicide Spray Decisions. One desire we all have is for fungicides to be used only when needed. Regular field scouting for foliar fungal diseases has been successfully used by growers for many years to determine if and when to spray fungicides in wheat. However, this is not possible with FHB since once symptoms are present it is TOO LATE to spray. Below are some general guidelines to help you determine if you should spray fungicides for FHB/DON suppression.

During period leading up to, during and immediately after head emergence:

Soil moisture has been good for the past month (relates to spore production, dispersal of Fusarium graminearum spores, and crop infection).

Crop has good yield potential (relates to economics and crop density, which increases canopy humidity and may increase spore production, facilitate spore dispersal, and encourage crop infection).

Temperatures 68-86 F (relates to spore production and crop infection).

Humidity is high (80% day or night) and/or free water (such as dew) is present on the heads during this period (relates to spore production, dispersal, and crop infection).

If most or all of the above conditions exist when the crop is just beginning to flower, consider spraying as soon as possible.

New Web-Based FHB Prediction Tool. In addition to the above general guidelines, an exciting new tool can also be used to help determine the FHB risk and need to spray. This tool is a web-based, disease forecasting model made available by Penn State University, The Ohio State University, Kansas State University, and the U.S. Wheat and Barley Scab Initiative. This forecasting model, utilizes real-time weather data from numerous National Weather Service stations within each state. Go to www.wheatscab.psu.edu/ and click on "Risk map tool".

You will be asked if you are growing winter or spring wheat. At this point you will come to a U.S. map and are asked to click on the state of interest. The FHB Risk Management Tool page will have a map that shows where the weather data are being retrieved. To the upper left corner of the page is a calendar section labeled "Assessment Date". This section needs a bit of explaining. You will note right away that the tool will only let you click on the current date and the preceding 7 days. So, if you estimate your crop will begin to flower (the beginning of FHB susceptibility) on May 7, but it is only May 3, the best you will be able to do is to determine if the weather on May 3 (or the previous 7 days) is favorable for FHB. My advice is to begin determining the FHB risk using this model 1-2 weeks out from crop flowering. Keep checking your wheat and keep checking the model every 1-2 days. By the time your crop reaches early flowering, you should have a good feel for the FHB risk in your area. If the forecast model says the FHB risk is high (medium if you are not a risk taker), and the forecast matches your local weather and crop reality, then you might consider spraying as soon as possible. The FHB Risk Management Tool also includes a commentary section that will give you a text risk assessment based on the opinion of the local state Extension Specialist (that’s me for KY).

Once you actually see it and play around with it, what I have said above will make much more sense. The model does have several practical limitations in predicting final FHB levels; these are clearly discussed within the Prediction Center web site. Perhaps the greatest limitation of the model is that it does not account for weather conditions during flowering and grain fill. Specifically, disease-favorable weather occurring during late flowering and grain fill can greatly impact final FHB/DON levels. The bottom line is that final FHB/DON levels may not always be reflected by the model’s risk output. The authors of the model discuss this limitation under "Reality Check" in the "Model Details" section of the Prediction Center.

We all hope that FHB is non-existent this spring. However, if this is not the case, wheat producers now have an additional tool to use to minimize FHB and DON development this spring.