First published in Kentucky Pest News.

Several wheat fields in Kentucky are now at the anthesis stage (Feekes 10.51, “flowering”) or fast approaching it. Anthesis is a critical time, as wheat becomes susceptible to infection by Fusarium graminearum, the primary causal agent of Fusarium head blight (FHB; also known as scab) in Kentucky (Figure 1). This disease can cause reduced grain yield, test weight, and quality. In addition, the fungus can produce toxins that will contaminate grain, such as deoxynivalenol (DON; also known as vomitoxin). Harvested grain with high levels of DON may be discounted or outright rejected at the elevator. To achieve the best management of FHB, different management practices must be implemented, such as planting wheat into fields that were previously cropped to soybean (rather than corn), planting wheat varieties with moderate to high levels of resistance to FHB, and applying foliar fungicides at the proper timing. Of these different management practices, the application of foliar fungicides is the only one that can be done during the growing season.

Fungicides

Proper fungicide application timing is critical in achieving the best efficacy. The best application timing is when plants are beginning to flower (early anthesis – Feekes growth stage 10.51), but some efficacy may still be achieved within a few days after Feekes 10.51. It is important to always follow the label recommendations and consider the preharvest interval (PHI) requirements, which can vary from product to product. Fungicide products that contain quinone outside inhibitor (QoI; strobilurin) active ingredients should not be applied for control of FHB, and most do not list FHB control or suppression on their label. In multiple university research trials, strobilurin fungicides have been shown to increase DON levels in grain compared to non-treated checks. Therefore, it is extremely important that only effective fungicides be applied for management of FHB. 

Some questions about the possibility of making two applications for management of FHB have been asked recently. A two-application system would include the first application at Feekes 10.51, followed by an additional application about 4-6 days later. The Bradley Lab at the University of Kentucky has evaluated treatments such as these, and some results from 2020 to 2022 are shown in Table 1. The results of these trials are a bit mixed, where an additional statistically significant decrease in DON was observed with multiple application treatments vs. a single application of Miravis Ace at Feekes 10.51, but an economic benefit would not always been likely. If a second application is made, it is important that labels are read and understood to be certain that the second application is legal. Some restrictions on the maximum amounts of active ingredients that can be applied could come into play as well as some restrictions on the latest growth stage that products can be applied and the pre-harvest intervals.

Table 1. Results of single vs. multiple fungicide application from research trials conducted in Princeton, KY. Single or first application made at Feekes 10.51 with second application made 6 days later.

*Prosaro sprayed in 2020 and 2021; Prosaro Pro sprayed in 2022 
**Caramba sprayed in 2020 and 2021; Sphaerex sprayed in 2022 
***LSD 0.05 = Least significant difference value with 95% confidence; NS = no statistically significant differences

When making a decision on if a fungicide application is needed, FHB risk should be assessed. An FHB Prediction Tool is available on-line here. This risk is based on weather conducive for FHB and should be assessed for each field as they begin to develop heads in anticipation of flowering. It is important to continually monitor the FHB Risk Prediction Tool as more and more wheat fields get closer to the anthesis stage.

Additional Resources

Some additional resources listed below may be helpful when making decisions about FHB management in wheat:

• “Fungicide Efficacy for Control of Wheat Diseases” on the Crop Protection Network (link)
• Results from the U.S. Wheat & Barley Scab Initiative Integrated Management Trials across several states (slides available here)
• U.S. Wheat & Barley Scab Initiative “Scabinar”, which discusses management of FHB (link)

Acknowledgement

This article references the results of research supported by the U.S. Department of Agriculture (USDA) under agreement no. 59-0206-0-183, which is a cooperative project with the U.S. Wheat and Barley Scab Initiative. This federal funding has been crucial for university scientists and USDA-Agricultural Research Service scientists across several states to discover and developing new ways to manage Fusarium head blight and the associated mycotoxins, such as deoxynivalenol (DON; “vomitoxin”), that can contaminate grain.