With the wheat maturing and harvest underway in parts of Oklahoma and Kansas, concerns of head scab or fusarium head blight (FHB) are present. Head scab will cause partial or completely white heads in the field but be aware that there are other causes for white heads. Dr.’s Romulo Lollato and Erick DeWolf from K-State do a great job of explaining the many causes of white heads in the most recent Agronomy eUpdate, which can be found here. The rest of this article will be focused on fusarium head blight and the concerns and problems associated with it.
Fusarium head blight is a fungal disease that mainly affects the heads in wheat, rye, barley, oats and triticale. The same pathogen also causes stalk and ear rots in corn. The disease prefers warm, wet conditions and infects the head if these conditions are present from flowering all the way through the soft dough stage. The earlier the infection occurs, the greater the severity of FHB.
Symptoms of head scab will have at least one spikelet or up to the entire head that appear prematurely whitened or bleached (Figure 1). FHB also causes a dark discoloration to the rachis (stem where the individual spikelets attach) directly below the infected spikelets (Figure 2). The area and severity of the head infected depends on when the warm, wet conditions occurred. Once infected, the FHB pathogen sporulates on the glumes and spikelets resulting in a pink to salmon color mass of spores (Figure 2).
FHB bleached spikelets are typically sterile or contain kernels, referred to as “tombstones,” which are shriveled and often have a chalky white or pink color (Figure 3). These infected kernels may also contain mycotoxins with vomitoxin, or DON, being the most prevalent which causes vomiting and decreased feed consumption in livestock. Overall the presence of “tombstones” leads to decreased test weight, decreased milling quality, and if DON is present, decreased feed quality. Also, if the infected field is being used for seed production, FHB infected kernels will have a decreased germination and seedling vigor compared to healthy kernels. Even some kernels that appear healthy can be infected with FHB in their seed coat causing a decrease in germination in what appears to be a healthy seed lot.
There are a few things that you can do as a producer to decrease your risk of head scab infection. Since the same pathogen can cause stalk and ear rots in corn, it is recommended that you do not plant wheat after corn. If you must plant wheat after corn, choosing a variety that has some tolerance to FHB, such as Everest or K-State’s new variety, Zenda, will decrease the severity of the disease. Plowing corn residue can also decrease the risk of FHB but is generally not recommended due to other agronomic reasons. Triazole fungicides such as Caramba and Prosaro can help mitigate head scab but must be applied as close to flowering as possible and with high volumes of water to maximize their benefit. Fungicide applications aimed at controlling scab are best if used in combination with varieties that have some FHB tolerance. Finally, managing irrigation timings to allow the crop canopy to dry between passes will also help decrease FHB severity if growing wheat under irrigation.
If you plan on saving seed from a field that was infected with fusarium head blight, there are a few steps that you can take to ensure that you meet the germination standards for that seed lot. To begin with, “tombstone” kernels are a lighter density than healthy kernels and can be removed with air screen cleaners and gravity tables, thus increasing both test weight and germination. Secondly, the fusarium pathogen that lives on the seed does not have a long life span and can actually die if the seed is stored for a long enough period during the heat of the summer. Finally, if the seed lot still does not meet germination specs without a seed treatment, most fungicide seed treatments on the market today are effective at controlling the fusarium pathogen on the seed.
In the rounds I have been making the past couple of weeks, fusarium head blight levels are fairly minimal. I think we are close enough to harvest or are harvesting in South Central Kansas and Central Oklahoma that FHB will not be a huge concern in these areas. As wheat continues to progress in North Central Kansas and South Central Nebraska, I strongly recommend farmers to be scouting for head scab. The wheat in this area is at the stage where scab is fairly noticeable if present. For the most part, the lack of moisture and warmer temperatures across the state this past week and in the forecast for the next week will help minimize further development of head scab.
By Bryson Haverkamp