Source: Kentucky Pest News

Fusarium head blight (FHB) of wheat, and deoxynivalenol (DON) accumulation in harvested grain, are periodically very serious problems in Kentucky. There was minimal FHB in 2005, but a 2004 FHB epidemic was very severe, and many producers experienced significant yield and grain quality losses.

On April 6, 2006 the Environmental Protection Agency (EPA) granted the Kentucky Department of Agriculture’s section 18 request to allow applications of Folicur 3.6F to suppress FHB/DON in Kentucky during 2006. This is the third year in a row that EPA has granted this request.

Folicur is manufactured by Bayer CropScience. The proper use of Folicur will reduce the risk of FHB and DON when used with other FHB/DON management tactics (see http://www.ca.uky.edu/ukrec/newsltrs/news03-2.pdf).

Let me say up front that Folicur is not a “silver bullet” for managing FHB/DON. A great deal of research suggests that about 30-40% reduction in FHB symptoms and DON accumulation is a reasonable expectation for winter wheat. Sixty percent control or more has been achieved in rare field studies in the U.S., but these are atypical results. In other words, do not expect Folicur to provide the same level of FHB/DON control as you have come to expect when fungicides are used to control other wheat diseases. The key is to think in terms of disease suppression, not control. Nevertheless, a 30-40% reduction in FHB and DON could have a significant economic impact locally, and state-wide, if FHB is moderate to severe in 2005. But be advised that significant losses due to FHB and/or DON may occur even where Folicur has been applied if weather conditions favor severe FHB this spring,

The section 18 label allows for a single ground or aerial application of 4 fl oz/A of Folicur 3.6 F to wheat through very early flowering (Feeke’s stage 10.51) or May 30th, whichever comes first. Applications cannot be made within 30 days of harvest. A copy of the section 18 label must be in your possession at the time of application.

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.

For ground application, research has shown that best head coverage is achieved with a double-swivel nozzle configuration of XR8001 flat-fan nozzles oriented forward and backward at a 45 degree angle. Acceptable coverage can also be achieved with a single nozzle configuration using TwinJet TJ8002 nozzles. When using either the double-swivel nozzle or the single TwinJet configuration, best head coverage is achieved when the boom is set 8 to10 inches above the heads, spray pressure is 30 to 40 psi OR 80 to 90 psi, fungicides are delivered in 15 or more gallons or water/A, and ground speed does not exceed 8 mph during application.

For aerial application, nozzles should be angled to direct spray 90 degrees to the direction of travel. Spray droplet size should range from 300 to 400 microns and Folicur should be delivered in no less than 5 gallons of water/A. It is best to spray early in the morning or at other times when heavy dew is present. This will facilitate fungicide coverage on heads.

Regardless of the method of application, be sure to tank-mix the lowest rate of a spray surfactant with Folicur to enhance coverage and optimize treatment effectiveness.

Folicur must be applied at a specific time, early flowering, in order to be effective. The optimal time for application is 25% of primary heads, scouted at several random sites in a field, showing anthers (pale, yellow-green structures about 1/8-in-long). Much beyond 25%, and it may be too late. The flip side - applying Folicur before full head emergence/early flowering can seriously compromise FHB/DON suppression.

This brings up a point of tension that wheat producers may face this spring. Delaying application of Folicur to achieve FHB/DON suppression could allow for excessive build-up of other fungal diseases. Conversely, application of other labeled fungicides before full head emergence will control other diseases, but will have no impact on either FHB or DON. I would advise growers that foliar disease development should take precedence since little is to be gained by suppressing FHB/DON if serious losses are incurred by allowing fungal foliar diseases to develop.

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. However, this is not possible with FHB since once symptoms are present it is TOO LATE to spray with Folicur. Below are some general guidelines to help you determine if you should spray Folicur for FHB/DON suppression this spring:

• Soil moisture has been good and rain is expected in the near future (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).
   
• Rain showers and/or free water were available 5-7 days before flowering (relates to spore release, dispersal, and crop infection).
   
• If most or all of the above conditions exist when the crop is at 10-15% flower, you should consider spraying Folicur within one or two days.
   
• An exciting new tool that can be used to help determine the FHB risk is a new web- based, disease forecasting model recently made available by Penn State University, Ohio State University, and the U.S. Wheat and Barley Scab Initiative. This forecasting model, which is reported to be 80+% accurate in predicting conditions conducive for FHB epidemics, utilizes realtime weather data from numerous National Weather Service stations within each state. When you enter into the “Risk Map Tool”
  section of the FHB prediction center home page, you will be asked if you are growing winter or spring wheat and, if winter wheat, whether the field has corn residue that covers 10% or more of the soil surface, regardless of tillage system used. At that point you will come to US map and are asked to click on your state. This will bring you to the main FHB Risk Management Tool page.
   
• The FHB Risk Management Tool page will have a map of Kentucky showing the locations in the state where the weather data are being retrieved. In the upper left corner of the page is a calendar section labeled “Flowering Date”. This section needs a bit of explaining. You will note right away that the model will only let you input a “flowering date” as late as the current day. It also covers the preceding 7 days. So, if you estimate your crop will flower 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 is favorable for FHB, and establish what the FHB risk has been for the preceding 7 days (April 26 to May 2). Of course, since your crop is not flowering, the real FHB risk is zero, no matter what the forecast model says. Nevertheless, that information will tell you if FHB is brewing or not. My advice is to begin determining the FHB risk using this model several days out from crop flowering. Keep checking your wheat and keep checking the model every 1 to 2 days. By the time your crop reaches 10 to 15 % bloom, you will 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 reality, then you might consider spraying Folicur within 1 to 2 days.
   
• The web address for the FHB Prediction Center is http://www.wheatscab.psu.edu/. 
  Check it out. 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. This is where the model failed us in 2004. Specifically, disease-favorable weather occurred during late flowering and grain fill and greatly impacted final FHB/DON levels. As I said earlier, the forecast model is 80+% accurate, so final FHB/DON conditions will 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 and that growers achieve record yields and grain quality as they did in 2005. However, if this is not the case, wheat producers now have an additional tool to consider, and possibly use, to minimize FHB and DON development this spring.