Among the many rice diseases we endure in the South, kernel smut (black smut) is one of the most aggravating to deal with. While all the reasons are not understood, kernel smut has increased in importance in recent years in different areas of Southern rice production.

So what can be done about it? In 1998, kernel smut wore us out in Arkansas on the high-yielding variety LaGrue, a favorite for parboiling. While kernel smut often does not cause major yield losses, heavily smutted rice cannot be parboiled without causing quality problems in the finished product.

Since 1998, using a combination of cultural practices, variety selection and the older rice fungicide, Tilt, most farmers have brought kernel smut under control on their farms.

In a nutshell, we recommend several options to minimize kernel smut in rice. These include:

  1. Pick the right variety for the field. Some varieties are more susceptible to kernel smut than others, so don't plant them in a field with a strong history of the problem. LaGrue is an example of a very susceptible variety. Wells has not been as susceptible — although all varieties will have some level of the disease under favorable conditions.
  2. Grow the variety right. Kernel smut likes heavy nitrogen fertilizer rates, so try to throttle back on the urea a little bit if you are consistently having problems with this disease. There is a magic rate of nitrogen where yield is as high as it will get while not encouraging severe disease. Extension recommendations will probably get you close to this, but you may have to experiment a little in your system to find the right rate for your farm. It has been our observation that total nitrogen rates above 160 pounds per acre get the kernel smut going and the more you put on above 160 pounds, the higher your risk for black combines. Invariably, I see the black combines in fields where more than 180 pounds of nitrogen per acre were applied.
  3. Use propiconazole fungicide to prevent kernel smut if you mess up on 1 and 2. Propiconazole is the chemical name for the fungicide in Tilt and Propimax, and it is one of the fungicides in the new product, Stratego — which controls both sheath blight and kernel smut. In our experience, propiconazole has worked very well in preventing high levels of kernel smut although there will always be a few smutted kernels no matter what. In our trials over the years, the proper time to spray this fungicide is during the swollen boot stage of rice. This means that you cannot scout for kernel smut but must make an application on faith, believing that you will have significant kernel smut in the field to be treated.

Factors that help your decision include:

  • Is the field planted to a susceptible variety like LaGrue, Cocodrie, Cypress, CL 121, etc?
  • Did you fertilize the field heavy?
  • Most importantly, have you had smut problems in the field in recent years?

If you answer yes to all the above, then the field is probably a candidate for the fungicide approach.

Can you spray too late? Yes. For one thing, propiconazole applications are illegal on heading rice, and it is also probable that applications later than boot will not be as effective in controlling the disease as earlier ones.

While kernel smut is one of the many aggravations in rice farming, it can be understood and controlled with a little planning and timely decisions. Good luck on a clean rice harvest.


Rick Cartwright is an Extension plant pathologist with the University of Arkansas Division of Agriculture.