Predicting Risk of
Fusarium Head Blight (Scab) in Wheat
Kiersten Wise, Assistant Professor
of Field Crop Diseases, Department of Botany & Plant Pathology,
Wheat in far southern Indiana reached flowering (Feekes
growth stage 10.5.1, Figure 1) this week, and wheat throughout southern
Indiana is in late boot stage or beginning to head. Wheat in central
to northern Indiana is still variable, ranging from early boot to
just past jointing (Feekes 7). In southern Indiana this is an important
time to consider the risk for Fusarium head blight development in
The fungus that causes head scab,
Fusarium graminearium, infects the wheat plant during flowering,
or Feekes growth stage 10.5.1. Rainy, warm, and humid weather conditions
favor disease development. Symptoms include bleached spikelets
on the head (Figure 2), and small or shriveled grain kernels, commonly
The fungus also produces hazardous toxins, such as deoxynivalenol,
or DON, which can accumulate in the infected grain. DON is toxic
to livestock, especially swine, and grain with DON levels between
1 and 3 ppm can reduce weight gain in animals. DON-infected grain
may also be subjected to dockage or refusal, depending on the grain
Crop rotation and selection of partially resistant varieties can
help prevent Fusarium head blight development, but timely fungicide
applications may be needed to prevent or manage the disease in-season.
There are several good fungicides available for Fusarium head blight
control, and these are listed in the foliar
fungicide efficacy table (pdf file) developed by the North Central
Regional Committee on Management of Small Grain Diseases or NCERA-184
Applications of fungicide prior to head emergence, such as those
applied at jointing or flag leaf emergence may not reduce FHB infection.
Also, some research has shown that fungicides containing strobilurin
modes of action(Headline, Quadris, Quilt, Stratego, Twinline, etc.)
increase the level of DON accumulation in FHB infected wheat (1,2).
Therefore, we do not recommend applying strobilurin fungicides for
Fusarium head blight control. Also, be sure to follow label restrictions
on how many days must pass between fungicide application and harvest.
Fungicides are an additional input into wheat
production, and are not always necessary, especially if the risk
of Fusarium head blight infection is low. Fusarium head blight
has not been as problematic in Indiana over the last several years;
however, the frequent rains and warmer temperatures could increase
the chances of Fusarium head blight development in 2009. There
is an excellent risk model tool available for growers to use to
assess the risk of Fusarium head blight infection in Indiana. This
model can be accessed through the following link: <http://www.wheatscab.psu.edu/>.
Weather conditions have been favorable for Fusarium head blight development
in far southern Indiana, and growers should be checking the model
to determine the approximate level of risk for their location. Additionally,
it is important to scout fields in southern Indiana to determine
the exact growth stage of wheat for optimum timing of any potential
At this site there are several links that explain
how the model was developed, and links providing additional information
about Fusarium head blight on wheat. To access the model directly,
click on the link marked “Risk Map Tool.” The first
screen will explain how to use the model. This model requires that
you know the approximate flowering date of your wheat variety,
and after reading the initial screen, you can click on calendar
to input the date that your variety is expected to flower. At this
point, if you click on the state map of Indiana, it will take you
to the local scab forecast, and you can calculate the Fusarium
head blight risk level for that specific area (Figure 3).
This model uses weather information including temperature, rainfall,
and relative humidity to calculate risk levels for Fusarium head
blight. Although it is a good tool for predicting risk, it has an
estimated accuracy level of 80%. Keep in mind that the model does
not provide a guaranteed prediction for whether or not scab will
occur in individual fields.
C.A. Bradley, E. Adee, S. Ebelhar, and B. Young. 2008. Fungicide
control of Fusarium head blight on soft red winter wheat in Illinois.
In: Proceedings of the United States Wheat and Barley Scab Initiative
2008 National Fusarium Head Blight Forum p. 10. Online at: http://www.scabusa.org/pdfs/forum08_proc_complete.pdf.
C.R. Hollingsworth and C.D. Motteberg. 2008. Determining potentials
for DON accumulation from prehead timing of fungicide application
on spring wheat and 6-rowed malting barley in Minnesota. In: Proceedings
of the United States Wheat and Barley Scab Initiative 2008 National
Fusarium Head Blight Forum p. 26. Online at: http://www.scabusa.org/pdfs/forum08_proc_complete.pdf.
Click image to enlarge
Fig. 1. Feekes growth stage 10.5.1.
Fig. 2. Bleached spikelets on the head of wheat (Photo courtesy
of G. Shaner).
Figure 3. Risk model predictions for Fusarium head blight development
in Indiana for May 8th.