In the past few weeks, there has been much discussion among Extension Specialists in the U.S. regarding recommendations for early and reduced rate applications of foliar fungicides for wheat. Currently, most foliar fungicide recommendations use the Feekes 8 (flag leaf visible) growth stage as the primary growth stage for when fungicide decisions are made. This timing is targeted at protecting that flag leaf and the leaves (F-1; F-2) directly below the flag leaf. These leaves contribute the majority of the photosynthates required for grain fill. Therefore, an early fungicide application would be one that occurs prior to this growth stage. Secondly, discussions have also centered on the use of a reduced rate fungicide application, which means one that is a tank mix application with early-spring herbicide applications prior to Feekes 5 (leaf sheaths strongly erect).

 

To date, results from University field trials around the U.S. have been inconsistent regarding if and when an early foliar fungicide application is warranted. In the majority of situations, optimal disease control has been when a fungicide application has been made close to the appearance of disease in a specific area. For example, in the southern U.S., early applications may be warranted on a case-by-case basis when stripe or leaf rust occurs early (Feekes 4 (beginning of erect growth) to Feekes 6 (first noticeable stem)), however, taking this approach for Wisconsin is probably not warranted since rust development occurs later. Furthermore, to help us make our management recommendations specifically for rust diseases on wheat, we monitor the distribution of the different rusts in the U.S. through the USDA Cereal Rust Laboratory (http://www.ars.usda.gov/Main/docs.htm?docid=9757). One specific situation where an early fungicide application has been recommended is in North Dakota. This has been targeted to tan spot, which can occur during the spring wheat growing season in North Dakota. Tan spot is favored under continuous wheat production and early season management may benefit late season damage, especially since infection of wheat seed by the tan spot pathogen is correlated with the severity of tan spot on the flag leaf. The North Dakota recommendation is for a foliar fungicide at the 4-5 leaf stage, however, whether this management approach is effective for other wheat diseases is not well known. In Idaho, results looking at reduced rate and early applications of fungicides have shown that highest yields were achieved when applications were made in the Feekes 8 (flag leaf visible) to Feekes 9 (ligule of flag leaf visible) growth stages and that applications made between these stages had the lowest percentage leaf area of foliar diseases.

 

Based on results around the U.S., we recommend that growers actively scout their fields for the presence of wheat diseases before making a foliar fungicide decision. We also want to emphasize that you should always follow the label recommendations for any fungicide in wheat since not all products are effective against all wheat diseases. In an effort to help Wisconsin’s growers make fungicide management decisions, we will publish in the Wisconsin Crop Manager over the next few issues articles about scouting and identifying wheat diseases.