Wheat in Indiana is starting to head out in central Indiana and flowering will probably start this weekend. During flowering (anthesis) warm, wet weather with high relative humidity will favor the development of Fusarium head blight (scab). Due to the recent cooler conditions, the risk remains low for the next 72 hours based on the Fusarium Risk Tool (Fig 1.) If you do choose to spray, aim for this early flowering period.
Our southern neighbors have started reporting multiple diseases in wheat, such as strip rust and Septoria leaf spot. We have yet to see many samples or reports here in Indiana. There are a number of resources are available to help distinguish wheat leaf diseases, they include the Purdue Wheat Field Guide (https://ag.purdue.edu/agry/dtc/Pages/WheatFG.aspx) 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
Figure 1. The 72 hour Risk Forecast for Fusarium, the map was generated on 20 May 2021. Orange = high risk, Yellow = medium risk, and Green = low risk for Fusarium head blight on wheat just prior to flowering or the early stages of grain development. Image credit: http://www.wheatscab.psu.edu/.
Fusarium head blight (FHB) is caused by the fungus Fusarium graminearium. It infects wheat during flowering, beginning at Feekes 10.5.1. Symptoms of FHB will appear as bleached spiklets on the head later in the season. 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 2. Wheat beginning to flower and Fusarium head blight infection. (Photo Credit: Darcy Telenko)
A number of resources are available to help you make disease management decisions in wheat.
1) The Fusarium Risk Assessment Tool is available at the following website. http://www.wheatscab.psu.edu/. This tool estimates the risk of a Fusarium head blight epidemic (> than 10% field severity) using weather conditions (temperature, rainfall, and relative humidity) measured 15 days prior to flowering. See above for the current risk map – Indiana is still green (low risk for scab development).
Keep in mind that actual disease risk depends heavily on the growth stage of wheat in your area. We are moving into flowering; the estimate is 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.
I wanted to remind you that this tool is available. Farmers and crop advisors can sign up for alerts from the U.S. Wheat and Barley Scab Initiative; these can be sent to a cell phone as a text or email. To sign up visit https://scabusa.org/fhb_alerts.
2) Fungicide Application: 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, Caramba, Proline, and Miravis Ace. 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 Tables for wheat were just updated and are available from the Crop Protection Network publications. https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-wheat-diseases-filename-2021-04-21-154024.pdf
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.
