Fusarium Head Blight (Scab) and Wheat Update

Darcy Telenko, Extension Field Crop Pathologist


Wheat is starting to head out across the central and northern Indiana, with flowering not too far behind. Our plots in southern Indiana hit early anthesis (flowering) last week and we put out our Feekes 10.5.1 fungicide trials out at Southwest PAC, Vincennes, IN. The wheat was 50% flower. Rainy, wet conditions can favor many fungal diseases in wheat. Our southern neighbors have started reporting multiple diseases in wheat. These include – strip and leaf rust. We did find Septoria leaf spot in the lower canopy in our southwest plots.

There are a number of resources are available to help distinguish wheat leaf diseases, they include the Purdue Wheat Field Guide (https://www.edustore.purdue.edu/item.asp?Item_Number=ID-448) and “Identifying Rust Diseases of Wheat and Barley.” https://www.ars.usda.gov/ARSUserFiles/50620500/Cerealrusts/Rust_Diseases_National.pdf

Samples can always be submitted to the Purdue Plant Pest Diagnostic Lab for disease identification and confirmation. https://ag.purdue.edu/btny/ppdl/Pages/default.aspx

Fusarium head blight (FHB) is caused by the fungus Fusarium graminearium. During flowering (anthesis) warm, wet weather with high relative humidity will favor the development of Fusarium head blight (scab). It infects wheat during flowering, beginning at Feekes 10.5.1 (Figure 1). Symptoms of FHB will appear as bleached spiklets on the head later in the season (Figure 1). Infection can lead to small or shriveled grain kernels referred to as “tombstones.” In addition to shriveled grain, this fungus can produce mycotoxins such as deoxynivalenol (DON), which can accumulated in the infected grain.

Figure 1. Wheat beginning to flower and Fusarium head blight infection. Photo credits: Darcy Telenko

Looking at the Fusarium Risk Tool wheat scab risk there are a number of areas starting to move into medium risk (orange color; Figure 2), there are also some areas that are red if wheat is planted to a susceptible cultivar. The risk is reduced if the cultivar is moderately susceptible or moderately resistant to Scab where most of Indiana remains in the low risk (yellow color; Figure 3). There’s a new feature on the Scab risk map that enables users to view graphs of recent trends in humidity and disease risk. The graphs are activated by clicking on any point in the risk map (Figures 4). Looking at this new feature if you have planted a very susceptible (VS) cultivar the forecasted risk is inching up into high risk (red).

Figure 2. Fusarium risk tool for May 9, 2024 for a susceptible cultivar.
Figure 3. Fusarium risk tool for May 9, 2024 for a moderately susceptible cultivar.
Figure 4. The new feature on the Scab risk map that enables users to view graphs of recent trends in humidity and disease risk. The lower graph plots the risk for each of the wheat models for very susceptible, susceptible, moderately susceptible and moderately resistant winter wheat cultivars. The trends show that if a very susceptible cultivar is planted the risk has moved to high if the wheat is currently flowering.

Keep in mind that actual disease risk depends heavily on the growth stage of wheat in your area.  We are approaching a critical time here in Indiana. These risk estimates are most relevant just prior to flowering (Feekes 10.5.1) or the early stages of grain development. Fusarium head blight risk is highest when there are three or more days with extended periods of high relative humidity and moderate temperatures (65 to 80°F) during the early stages of kernel development.

A fungicide application might be considered if a Fusarium head blight (FHB) susceptible variety is planted, or if you are worried about scab on your farm. These applications should be made at Feekes 10.5.1, or early flowering to suppress FHB. Fungicides recommended for FHB and DON include Prosaro, Proline, Miravis Ace, and Sphaerex. The use of products containing strobilurin fungicides may result in higher levels of DON accumulation in grain when damaged by FHB. These are not labelled for FHB management. 

Fungicide Efficacy Tablesare updated yearly and available from the Crop Protection Network publications https://cropprotectionnetwork.org/publications/fungicide-efficacy-for-control-of-wheat-diseases

These tables can help you identify products to use based on your targeted disease. As a reminder follow the label on harvest restriction as some products may have 30 to 45 days required between last fungicide application and harvest. Once the full head has emerged flowering will likely occur in 3-5 days, depending on weather and variety. It is time to keep an eye on your fields. Those most at-risk would-be fields that were planted to a Fusarium head blight susceptible variety or those with limited rotation that follow a previous crop of wheat or corn.

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