Be Proactive and Manage Kernel Smut and False Smut in Rice

by Yeshi Wamishe, Extension Plant Pathologist - July 5, 2022

Fungi for kernel smut and false smut can infect both conventional and hybrid rice, if susceptible or moderately susceptible. Best cultural practices are highly recommended over fungicide applications to reduce damage due to these diseases, particularly false smut. Kernel smut and false smut are severe under these favorable conditions:

1. Late planted susceptible rice grown in a field with a history
2. Fields applied with excessive pre-flood nitrogen fertilizers
3. Fields with a dense canopy
   
   

Scouting for Kernel Smut and False Smut

Scouting is not recommended. Once these diseases show up, it is already too late for fungicide application or engagement of any cultural practices.

Application of Protective Fungicides

Fungicides need to be applied as a protective measure, although they will not provide 100% protection or disease suppression. Fungicides used in recent years include Triazole fungicides (Tilt equivalents) mostly containing Propiconazole, or Difenoconazole. 

Fungicide Application Timing

Early boot to mid-boot application is recommended. Mid-boot is the optimum timing. More delayed application reduces benefit from fungicide application.

Fungicide Rates

The kernel smut fungus is more sensitive to fungicides than the false smut fungus. In recent years the recommendation was at least 6 oz/acre rate of Tilt or Tilt equivalent. If you are to use Quilt Xcel, the minimum you could use is a 21 oz/acre rate, which contains a 5.9 oz/acre rate of Tilt. If you must use Amistar Top, you should consider a minimum rate of 12 oz/acre rate.

Efficacy Levels of Fungicides to Suppress Kernel Smut or False Smut

Based on past studies, the kernel smut pathogen is more sensitive to these fungicides with up to 90% - 95% disease suppression if applied at the correct timing, rate and canopy coverage. False smut was suppressed at 50% - 70%.


Pairing Rice Diseases for Fungicide Application

Application cost may be reduced when pairing protective fungicides to suppress the smuts with prophylactic application for sheath blight. Pairing fungicides is possible if sheath blight is at threshold at around mid-boot. You may use pre-mix fungicides or mix them yourself at the correct rates. 

Note: Do not attempt to pair protective fungicides for the smuts with neck/panicle blast. Late boot is the earliest timing for fungicide application against neck blast. By this time, a fungicide application will be too late for protection against the smuts. However, if sheath blight is progressing slowly, then fungicide application can be paired for sheath blight and neck/panicle blast.

Tips for the Most Benefit from Fungicide Application

• Well-managed fields benefit more from a fungicide application.
• Apply fungicides at recommended timing and rate to maximize their benefit.
• Fungicides mixed and applied using an adequate volume of water provide better coverage.
• If tank mixing, fungicides need to be checked for compatibility
• When tank mixing, compatible product rates can be adjusted as required.
• Rotating chemistries with different modes of action helps delay the development of fungicide resistance.
• Avoid automatic application with no disease potential - i.e., field history, susceptibility of the variety, excessive seeding and nitrogen rates.
• For sheath blight, scout to make an effective economic decision.

Figure 1. Kernel smut affects both yield and quality.

Figure 2. Rice grain mixed with false smut galls affects quality.