The leaf diseases leaf rust, stripe rust, tan spot, Septoria tritici blotch, and powdery mildew are the most common cause of disease-related yield loss. Often, leaf diseases are managed by a combination of genetic resistance and crop rotation; however, foliar fungicides may be needed when these practices fail to keep diseases at low levels.
This year, so far there have been some reports of wheat stripe rust in Kansas over the past two weeks. Low levels of stripe rust were detected in several counties in S. Central Kansas during the last week of April. So far the disease is restricted to the middle canopy and still at a very low incidence. This past weekend low levels of stripe rust have been reported in Ford, Saline, Dickinson, and Geary counties. The disease is still at low levels and in the middle canopy. The disease is mostly occurring on known susceptible varieties. However, even if you are growing a variety that has resistance, scouting wheat fields is still advisable. Many growers may be evaluating the potential need for fungicides over the next 7-14 days.
To highlight some key points from a K-State Research & Extension (KSRE) publication that answers common questions about the role of fungicides in wheat disease management and helps evaluate the need for a fungicide by analyzing information available at the time of application. The entire publication, MF3057 “Evaluating the Need for Wheat Foliar Fungicides,” can be viewed at https://bookstore.ksre.ksu.edu/pubs/MF3057.pdf
When should a fungicide be applied relative to crop growth? Fungicides can best protect these critical growth stages from disease when applied between full emergence of the flag leaf and anthesis (flowering). Diseases that damage plants at these early stages often reduce the grain yield significantly. Fungicide applications made before flag leaf emergence generally result in less disease control on the upper leaves during grain development and smaller yield responses. Always check and follow product label recommendations to ensure full compliance with growth-stage limitations and pre-harvest intervals.
How long will the fungicide provide disease control? The residual life of the fungicide application is influenced by the product used, rate of application, and disease targeted for control. In general, products belonging to the triazole and strobilurin classes of fungicide will provide 14 to 21 days of disease control. Small differences in residual life among products typically do not result in large differences in grain yield.
In general, the fungicides stay near the site of application or move toward the leaf tip. The fungicides only protect leaves, stems, and heads present at the time of application.
Are there important differences in how well various fungicide products work? Nearly all fungicide products labeled and widely marketed for use on wheat in Kansas contain active ingredients belonging to triazole, carboxamides and strobilurin classes of fungicides or mixtures of these classes. Both fungicide classes are effective at controlling common leaf diseases in Kansas. Products containing only the triazole class of fungicides are the best option in areas prone to Fusarium head blight (head scab). There are a few options containing triazole + carboxamides that would also be a good option of head blight control. More information about product options and efficacy against diseases can be found in the KSRE publication EP130 Foliar Fungicide Efficacy Ratings for Wheat Disease Management.
What is the typical yield response of wheat to foliar fungicides? Researchers with KSRE have been evaluating the potential role of fungicides in leaf disease management for many years. In most situations, these experiments were specifically designed to evaluate the benefits of fungicides when susceptible varieties are grown in environments extremely favorable for disease development. A summary of decades of experiments indicates that a single fungicide application between flag leaf emergence and anthesis often results in a yield increase between 4 and 14 percent, with an average yield increase of 10 percent. These figures can be combined with yield potential of a wheat crop to estimate the potential yield response in bushels per acre.
Because the yield response to fungicides is variable, it is often helpful to consider different approaches that can maximize the potential benefits of the fungicide application. Set priorities based on a variety’s balance of genetic resistance, susceptibility to disease, yield potential, weather information, and potential freeze injury this year before adding additional input costs.
Information provided by Erick DeWolf, K-State Wheat Pathologist.
Stacy Campbell is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at firstname.lastname@example.org or calling 785-628-9430.