Fusarium head blight (FHB) or scab was spotted the week of April 16, 2023 in southwest Alabama. FHB is an economically important disease of wheat and barley, as it can cause yield losses of more than 45 percent if not treated. It is caused by the fungal plant pathogen called Fusarium graminearum, which can produce DON (vomitoxin), a harmful toxin to livestock and humans. High humidity and frequent rainfall increases the risk for FHB. Wheat is most susceptible to FHB infection at flowering (Feekes 10.5.1) through early dough stage (Feekes 11.2).
FHB symptoms are found on the wheat head, grain, and sometime the stem, near the wheat head (peduncle). At the beginning, individual, some, or all of the spikelets on infected heads will be bleached, while healthy heads are still green (Figure 1). As the fungus moves into the rachis, spikelets located above or below the initial infection point may also become bleached. During wet, humid weather, pink or orange masses of spores may be visible on infected spikelets (Figure 1). Infected kernels will appear discolored, shriveled, and are lightweight.
The integrated pest management strategy for FHB relies on selecting resistant wheat varieties, planting high-quality seed, cropping practices, and preventative fungicide applications. Unfortunately, there are no resistant barley varieties available.
There are several fungicides labeled for use against FHB. These are most effective when the risk is medium to high. In wheat, fungicide applications are most effective at flowering, when the yellow anthers start to show on the heads. In barley, applications are most effective at heading, when the heads emerge from the boots. The following products are all labeled for use and have good efficacy against FHB.
- Caramba at 10 to 17 fluid ounces
- Proline 480 SC at 6.5 to 8.2 fluid ounces
- Sphaerex at 4 to 7.3 fluid ounces
- Miravis Ace SE at 13.7 fluid ounces
- Prosaro Pro SC at 10.3 to 13.6 fluid ounces
However, fungicides containing QoIs (FRAC code 11; strobilurins) should be avoided after the flag leaf stage, as they can increase DON (vomitoxin) in a scab epidemic.
Miravis Ace, Sphaerex, and Prosaro Pro are the most effective in reducing FHB. In wheat, these should be applied at early flowering or up to several days later. In barley, these should be applied about 6 days after full heading.
Currently, wheat and barley across Alabama are at different growth stages and fungicide applications will not be practical in all cases. For specific recommendations, producers should utilize the disease management section of Alabama Extension’s Small Grains IPM Guide and the North Central Regional Committee on Management of Small Grain Diseases’ Crop Protection Network publication Fungicide Efficacy for Control of Wheat Diseases. Producers should also continue to monitor their risk using the Fusarium Risk Tool available at www.wheatscab.psu.edu/. The good news is that dry weather will reduce risks moving forward in some parts of Alabama (Figure 2). The risk for FHB is highest in southwest Alabama, but it decreases as you move toward central and north Alabama, which carry a low to medium risk.