Cultural disease management strategies are beneficial in reducing kernel and false smut disease pressure. Historically, both kernel and false smut are severe in late-planted, susceptible rice cultivars raised in a field with a history of these diseases and that have had excessive nitrogen fertilizer application.
Under favorable conditions most rice cultivars, including hybrid rice, are susceptible.
Applied at the correct timing, rate and canopy coverage, the kernel smut pathogens are more sensitive to the fungicides with up to 90% to 95% disease suppression. With false smut being a newer and emerging rice disease, it has been found that the triazole fungicides can suppress the disease only from 50% to 70%.
The rate for the Tilt equivalent has been increased from 4 fl oz/ acre rate to a minimum of 6 fl oz per acre since 2012. The optimal timing recommendation is from early boot to mid boot (Figure 1). Fungicide application before early boot is too early since the fungicides may not remain effective until after the flowering stage.
Fungicide application timing after late boot is too late. Early or late boot split is too late (Figure 2). If you have to wait longer, it should not be until boot split. This is unfortunate because this has to be done a little earlier than the protection application for neck blast (neck rot).
The most common mistake in fungicide application is waiting for too long.Scouting for kernel or false smut is not recommended to plan for fungicide application. Once either or both of these smuts show up, it is already too late for fungicide application.
Fungicides should be protective and need to be applied at the correct timing for optimum suppression. Triazole fungicides containing Propiconazole (Tilt equivalents) are still the available preventative fungicide options.
Figure 1. Early to mid-boot is the optimum timing for kernel and false smut fungicide application.
For adequate canopy coverage, use a minimum of 10 gallons of water per acre to mix and apply the fungicides. Stand-alone fungicides such as Tilt, Bumper, Propimax or combination fungicides such as Quilt Xcel or Stratego can used.
Figure 2. Protective fungicide application to suppress kernel and false smut after late boot is not beneficial. It is already too late. Early or late boot split is also too late.
Tips for getting the most benefit from fungicide applications
- Well-managed fields benefit more from fungicide application.
- Fungicides applied at recommended timing and rate maximize their benefit.
- Fungicides mixed and applied using adequate volume of water provide better coverage.
- If tank mixing fungicides, check for compatibility.
- Rotating chemistries with different modes of action helps delay the development of fungicide resistance (there are no options for the smuts’ protection)
- Avoid automatic application where there is no disease potential to cut expense.
- Tank mixing compatible products by adjusting rates as required cuts cost over pre-mix fungicides.
- Using higher rates can cut down cost by cutting down the frequency of fungicide applications (this works more for sheath blight). In particular, scouting for sheath blight helps determine fungicide rate, timing and necessity.
- Check the content of active ingredient of fungicides of your choice and adjust the rates. For example, the highest rate for Stratego only contains 5.5 fl oz/acre rate of Tilt equivalent. Going for lower rates of Stratego can lower this rate (Table 1).
- To read more on fungicide rates and timing for major rice diseases, read: Rates and Contents of Fungicides; Fungicide Timings for Selected Rice Diseases.
Table 1. Rates and active ingredients in Stratego
