Thanks to the researchers at Penn State University, Ohio State University, Kansas State University, Purdue University, North Dakota State University, and South Dakota State University, we have a new wheat disease prediction tool available to wheat producers East of the Rocky Mountains. This new tool comes in the form of predictive models which are designed to forecast an outbreak of Fusarium head blight (FHB)(head scab) in wheat.
According to the University of Kentucky, economic losses resulting from head scab were in excess of 3 billion dollars in the 1990’s. It’s a devastating disease, and a considerable amount of effort has been put forth in an attempt to minimize it’s impact. The FHB prediction tool is a direct result of that effort.
The main benefit to those who grow wheat is the ability to predict a disease outbreak before it happens. This is especially welcomed in the case of FHB because you can not scout for this disease. If you find that you have the disease, it’s too late – the disease has already done it’s damage and caused a yield loss. This has caused many growers to move to a planned fungicide application across every acre every year – regardless of whether or not environmental conditions are favorable for disease development. The problem with this approach is that it results in a lot of fungicides being applied when they are not needed. Now however, we have a viable alternative.
According to the developers, the models can predict an FHB epidemic of greater than 10% severity at an accuracy rate of 80%. It accomplishes this high rate of accuracy by analyzing weather variables that occur before flowering. More specifically, for winter wheat, the model “considers the duration of time that relative humidity is 90% or greater and temperature is also between 48 and 85°F (9 -30°C).” For spring wheat it’s a bit different in that the model incorporates varietal resistance into the equation, but weather is again an important factor.
The key feature in obtaining a prediction for your wheat crop is the Risk Map Tool. It’s an easy to use web based interface that allows for a quick assessment of the potential for a FHB outbreak in any given area. In just a matter of a few clicks, you can see whether or not your crop is at risk. There are however a few key items of information that you will need to know beforehand. The prediction center recommends the following:
Key Items Needed to Obtain a Prediction
Flowering date– You will be asked to identify the flowering date for your fields. Visit fields to determine the date when anthers are exposed on 15% of the heads. Wheat is most susceptible during the flowering growth stage, and the models will use weather conditions observed during the seven days prior to the flowering date you select. Planting date and variety will affect flowering dates so each field may have a different flowering date. (You can use the 24 and 48 hour forecast buttons in the upper left corner of the tool to help you estimate risk several days before the actual flowering date).
We suggest that you monitor the risk of disease in your area for a full week prior to flowering. As the wheat crop approaches the actual flowering date, we recommend that you also monitor your local weather forecast. The greatest risk for scab occurs when weather conditions prior to flowering have been conducive for reproduction of the fungus (indicated by yellow or red colors on the risk map), and when weather during the early stages of kernel development favors infection. Three or more days with frequent rainfall and moderate temperatures (65 to 80 F) during the kernel development may significantly increase the risk of head scab.
Wheat class– Identify whether you are growing a spring wheat (spring planted) or winter wheat (fall planted). This selection will activate different components of the system and customize the prediction for your crop.
Production practices– If you select spring wheat, you will be asked to provide information about the resistance level of the variety planted in your fields. This is important because planting a susceptible variety may significantly increase your risk of disease. Most varieties of wheat are susceptible to head scab, and we advise that you use this as the default level of resistance unless you know that your wheat variety has a different level of resistance to head scab. More information about the resistance level of spring wheat varieties can be found in the variety evaluation reports provided by North Dakota State University.
With the above information in hand, you’re now ready to use the map tool. Just follow the three easy steps at the beginning, and you’ll soon have a map something like the one shown below.
Be sure to choose the weather station closest to your field so that you can get a more detailed assessment of the risk for a disease outbreak. You’ll also get a summary of the conditions during the past 7 days for that particular area as well as a risk rating of low, medium, or high.
There is one drawback to the prediction model – it can’t predict future weather conditions. As you and I both know, the weather can change in an instant. Conditions may not have been favorable for disease development, but it could be in the near future, so the decision to apply a fungicide should be based not only on the model but also on the weather forecast over the next 7 to 10 days.
As an agronomist, I can’t stress the importance of using this new tool. Any application of fungicide should be based upon the potential risk of disease development rather than treating every acre every year regardless of whether conditions warrant an application or not. I know some will argue that applications are warranted based upon a “plant health” standpoint alone, but field trial data does not back this up. The data clearly shows that a return on investment is consistent with the level of disease present in the crop. Under conditions of low or no disease presence, the return per dollar invested is very inconsistent. The only exception is for grain grown for food or seed. Fungicides can increase grain quality which oftentimes results in a higher premium, so that has to be taken into consideration. Otherwise, if you don’t need it, don’t spray it.