Fusarium head blight in wheat: Questions and Answers
What is causing the white kernels in harvested wheat?
Wheat harvest began in earnest in many areas of the state this week. In some cases, farmers may be seeing some white, chalky kernels intermixed with otherwise normal looking grain (Figure 1). These white kernels are often an indication that Fusarium head blight (head scab) infections that took place weeks ago when the wheat was flowering or at the early stages of grain development. While it is possible to see the symptoms of infection in the field during the dough stages of kernel development, most people don’t realize they have a problem until they see the Fusarium-damaged kernels in the grain.
Figure 1. Symptoms of wheat grain damaged by Fusarium head blight. Photo by Erick DeWolf, K-State Research and Extension.
Where did the Fusarium fungus come from?
The Fusarium fungus survives in the debris of many different types of grasses. In agricultural systems, the fungus is most likely to survive on the debris from previous corn and wheat crops. Planting wheat directly into fields with large amounts of crop residues on the soil surface increases the risk of disease. The local effect of the residue is diminished in years when weather conditions are highly favorable for the reproduction of the fungus. In these years, the Fusarium spores are moved considerable distances by wind and all fields are at risk for severe disease regardless of previous crop or amount of local residue.
Could fungicides have helped prevent Fusarium head blight?
Fungicides provide only partial suppression of Fusarium head blight. The triazole class of fungicides, such as Prosaro and Caramba, provide about 40-50% suppression of the disease. Products such as Folicur and Tilt provide 20-30% suppression. Other fungicides provide very little protection and are not labeled for the disease. Application timing is a significant issue for obtaining even these moderate levels of control of Fusarium head blight. The fungicide must be applied after heading to be effective. The most effective fungicide applications are timed to coincide with flowering or the early stages of kernel development.
Is there anything that can be done to address the Fusarium infection now?
During harvest it may be possible to reduce the amount of Fusarium-damaged kernels by adjusting the combine to remove the diseased kernels. Of course, there is a practical limit to benefits of these adjustments because some healthy grain will be lost at the same time. The bottom line is to try some different adjustments. See what you can do to reduce the amount of scabby kernels in the harvested grain.
If you have on-farm storage, you might also want to allocate part of your storage for holding the most severely damaged grain. Price discounts are often most severe at harvest and may decrease as an elevator or grain terminal has a better understanding of the overall grain quality they have to work with this year. Storing the grain temporarily on farm can offer some flexibility when marketing Fusarium-damaged grain.
Fusarium-damaged grain can be used for seed but you will want to take some extra precautions to ensure seed quality before planting the next crop. The Fusarium fungus can reduce germination of seed and cause seedling blights when the infected seed is planted. In some cases, plants that do survive may develop a root rot as mature plants. Fungicide seed treatments can help address these problems. Many of the widely marketed seed treatment products are labeled for control of seed-borne Fusarium and suppression of Fusarium root rot. More information about seed treatment options can be found in the publication: Seed Treatment Fungicides for Wheat Disease Management, 2015 (MF2955) at: http://www.ksre.ksu.edu/bookstore/pubs/MF2955.pdf
Erick DeWolf, Extension Plant Pathology