By Yeshi Wamishe, Extension Rice Pathologist
- I have my fields planted with hybrid rice this year. They were all planted early in the last week of April. Do I need any fungicide application for kernel smut (Figure 1) or false smut (Figure 2)?
Most hybrid rice varieties are susceptible to one or both smuts. Your decision for protective fungicide application for the smuts needs to consider the field history, pre-flood nitrogen fertilization rates, varietal susceptibility, and planting date. Warm and wet weather is often favorable for kernel smut but false smut is more favored by cooler temperatures than needed for kernel smut. Excessive nitrogen applications encourage both diseases. False smut is often seen more in late-planted susceptible varieties. Fungicide decision often requires your judgement based on all these factors together.
- If I already knew the variety is susceptible for kernel and false smut but my field has no history of either of these diseases, do I need to protectively spray for the smuts?
If pre-flood nitrogen is adequate, fungicide protection for the two smuts is not recommended in such fields.
- I know the rice variety I planted is susceptible, nitrogen fertilization is based on NSTAR recommendation and the field was planted relatively early. Do I need protection fungicide for the smuts?
No, it is not likely for the smuts to be severe in such fields.
- In my other field, I have pushed a little more pre-flood nitrogen. Do I need to worry about kernel smut in it?
A little more does not tell how much more. You should be able to tell the differences between rice fields having similar varieties by looking at the color of the leaves and the vegetative growth of the rice. If it is really excessive, it is of concern.
- What are the factors I need to know to make a good decision for protection fungicide to suppress the two smuts in rice?
Varietal susceptibility level, field history, seeding and pre-flood nitrogen fertilization rates, and planting dates.
- I need to prevent smut infection because my field has a history and the variety is susceptible. Sheath blight pressure at the moment is low and is not at a threshold level. Should I use Stratego to suppress both the smuts and sheath blight or just use tilt for the smuts?
Stratego has tilt in it. Either would work to suppress the smuts. You can wait until mid-boot (boot swollen, flag leaf not fully extended), to weigh out the sheath blight pressure. If the variety is tall and the weather forecast is not favoring its development, I would worry less about sheath blight and apply Tilt at the right rate. However, if threshold is reached, use combination fungicides such as Stratego, Quilt Xcel or Quilt to address both diseases. Sheath blight is a concern if it is aggressively moving, threatening the upper two or three leaves. Note that in some fields, fungicides for smut and sheath blight suppression are synchronized.
- Which fungicide is best for smut protection?
So far, our options are only the triazoles for the two smuts in rice.
- Do you have information on fungicide rates and timings for most rice diseases?
Yes, go to Rice fungicides timing and rates. The recommended timing for protective fungicides for kernel and false smut is early boot to mid-boot. Boot split and beyond as shown in Figure 1 is too late.
Fig. 3. It is too late to apply fungicides for kernel and false smuts late boot and beyond. Optimum timing is mid-boot.