Friday, September 24, 2021

Follow best application timing to maximize control of smuts

• By Yeshi Wamishe and Jarrod Hardke •

early boot rice
Fig.1. Early to mid-boot is the optimum timing for kernel and false smut fungicide application — photos courtesy University of Arkansas

In flooded or furrow-irrigated rice, most cultivars including hybrids are susceptible or moderately susceptible to kernel or false smut or both. Under favorable weather conditions, kernel and false smut are generally severe in late-planted susceptible rice grown in a field with a history and/or having dense canopy and receiving excessive nitrogen fertilizers.

Appropriate cultural practices are highly recommended to reduce the severity levels of both diseases. Scouting for kernel or false smut is not helpful to plan for a fungicide. Once the diseases appear, it is already too late for a fungicide application.

The recommended fungicides are protective and need to be applied between early boot to mid-boot (Figure 1).

Mid-boot is the optimum timing. The benefit from fungicide use continues to decrease if applied after mid-boot, and applying at boot split (Figure 2) is too late.

late boot rice
Fig. 2. Applying protective fungicides after mid-boot to suppress kernel or false smut is too late.

Triazole fungicides containing propiconazole (Tilt equivalents) or difenoconazole arecommercially available fungicides to suppress these diseases. When the fungicides are applied at the correct timing and rates using an adequate water volume, 90% to 95% suppression can be attained in kernel smut.

While the false smut fungus is less sensitive to the chemistries, research has shown 50% to 70% suppression using triazole fungicides. A minimum of 6 fluid ounces per acre of Tilt or Tilt equivalent is recommended.

To suppress kernel and false smut, triazole fungicides such as Tilt, Bumper or Propimax can be used. If premixes are desired, Quilt, Quilt Xcel or Amistar Top can be used.

When Stratego or Flint Extra are used, adjust the Tilt equivalent to at least a 6-fluid-ounce-per-acre rate. Check out the blog on rice fungicides and mix rates. Read fungicide labels carefully before mixing or application. Labels are the rule.

Sometimes the recommended fungicide timing for smut suppression may align with the sheath blight at the threshold level. In such situations, combination fungicides may be used to address the three diseases together and save additional application costs.

For adequate canopy coverage, a minimum of 5 or up to 10 gallons of water per acre are encouraged.

Dr. Yeshi Wamishe is Extension plant pathologist – rice. Dr. Jarrod Hardke is rice Extension agronomist. Both are with the University of Arkansas.

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