As wheat starts to green-up across the state, questions are coming in about the benefit of early fungicide applications.
Research at K-State and in other regions continues to demonstrate that it is often possible to achieve high levels of foliar disease control with a single fungicide applied between flag leaf emergence and heading growth stages. The yield response to this later fungicide application is influenced by the level of disease risk (amount of disease and predicted weather conditions), variety resistance to the most threatening fungal diseases, yield potential of the crop, foliar fungicide efficacy, and other factors.
Fungicides can also be applied as an early application made between “spring green-up” and jointing. This application may provide some yield benefit in some fields and years. It’s important to note that an application during these early stages of crop development is not a substitute for a flag leaf application, as any leaf that emerged after the application will not be protected. Early fungicide applications may result in small yield advantages due to a reduction in early disease establishment in the lower canopy. This may be particularly true for “leaf spot diseases” such as tan spot or Septoria leaf blotch that survive in wheat residue and can establish early in the year. Yield benefits are most likely in wheat fields planted back into wheat stubble and when weather conditions are wet enough to favor fungal disease development.
If deciding to make an early application, it is important to factor that into the full season fungicide program. Many active ingredients have use restrictions, where a limited amount of an active ingredient can be applied during a single season. It is important to make sure the early fungicide does not limit options for fungicide applications at flag leaf (which have the potential for higher yield protection in conducive disease years).
Advantages and limitations of split applications
These are some advantages to making an early application:
- Low cost. There is no additional cost for application if the fungicide is tank mixed with other products, such as liquid nitrogen fertilizer or herbicide. Often, however, the optimal timing for an early fungicide application is not until after the wheat has jointed – with one or two joints present. This is usually sometime in mid- to late-March in southern Kansas and later in northern Kansas. Top-dressed nitrogen and many postemergence herbicides should be applied before this stage to be most effective and, in many cases, to be within label restrictions, so the optimal timing of both applications may not match. A separate trip for an early fungicide application adds to the cost of production.
Since the payoff for an early application is less certain than with later applications, it is perhaps best to consider using a low-cost generic fungicide for the early application and saving more expensive products, if desired, for the later application.
- Provides suppression of early-season disease caused by tan spot, powdery mildew, and septoria leaf blotch (Figures 1 & 2) that overwinter locally in Kansas. The benefits of fungicides applied at green-up is more sporadic for diseases like leaf rust and stripe rust (Figure 3), which are less likely to survive the winter in Kansas. The rust diseases typically blow into the state from Texas and Oklahoma during the spring, and often become established as the crop transitions from jointing to flag leaf emergence. If a field has hot spots of stripe rust at jointing or earlier, a fungicide application made at jointing could help suppress the developing epidemic. However, a second application will be needed to protect the flag leaves during the early stages of grain development.
The limitations of early-season fungicide application include:
- Leaves not present at the time of application will not be protected. Therefore, these applications will not control leaf rust or stripe rust epidemics that come in from the south at later stages of growth. The early applications are most effective when combined with a second, later application of a fungicide.
- Additional product cost may not pay off under some conditions, especially this growing season when the yield potential of the crop may be limited by drought. Remember, the second application does the heavy lifting in the dual-application approach. If capital resources are limited because of low prices, it may be best to invest your money where you are likely to see the largest yield response.
Product rates and restrictions
Producers considering the use of split applications must pay close attention to label restrictions. Every active ingredient in a fungicide has a maximum total amount that can be applied during the season.
For example, if an early application of a generic form of tebuconazole is applied at 4 oz/acre, a subsequent application of any fungicide containing tebuconazole alone or in combination with other ingredients (e.g. premix) around heading could put you over the limit for the crop season. Thus, be sure to read the label to determine the maximum amount of a chemical that can be applied in a single season and the exact amount of a chemical(s) that is in a fungicide.
For information on the efficacy of different foliar fungicide products, refer to K-State Research and Extension publication: Foliar Fungicide Efficacy Ratings for Wheat Disease Management 2023, EP130.
The main conclusions we can draw from recent studies in Kansas and Oklahoma are:
- In K-State studies, the greatest average profit has come from the flag leaf application of fungicides. Fungicides applied prior to jointing are less likely to result in a positive profit.
- The likelihood of profit for an early-season fungicide application is greatest for susceptible varieties in continuous wheat systems with a high level of surface wheat residue.
- Fields with hot-spots of tan spot, septoria leaf blotch, and stripe rust prior to flag leaf emergence are candidates for an early fungicide application, provided environmental conditions are conductive for further disease development and yield potential of the crop. These applications are often most effective when made around the jointing stages of growth.