This year we moved out of the cold and cool conditions of March and moved straight into summer, bypassing any of the gradual warming typical of spring. The summer temperatures have our rice developing at a fast and steady pace this year. Most of the rice in southwest Louisiana has received its mid-season nitrogen fertilizer and it is now time to shift gears and begin thinking of our disease management plan.
The winter was long and we have had hot conditions with little rainfall and a lower than normal humidity so far this year. These conditions suggest that disease potential will be lower-than-normal. However, we are having trouble keeping water on the field in some places which increases the potential for blast.
We also have several thick stands of rice which increases the potential for sheath blight. Weather conditions can change overnight too, so our low rainfall, low humidity and clear blue skies can change to frequent showers, extended overcast conditions and high humidity which favors disease development.
The bottom line is that we should be sure to scout for disease and apply fungicides when needed to prevent any disease outbreaks.
Blast can be one of the most devastating diseases in rice. Strobilurin (Group 11) fungicides are labeled for use in rice to manage blast. These include Quadris, Equation and Gem. They are also available mixed with propiconazole fungicides which include Quilt, Quilt Xcel, Stratego and Amistar Top.
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If a one-shot application of a fungicide is to be used for blast control, it should be applied when 50-70 percent of the panicles are just beginning to emerge from the boot. This is sometimes referred to boot split. This cannot be seen from the truck and must be observed from the in the field. This is not to be confused with 50-70 percent fully headed rice.
If significant leaf blast is observed in the late tillering stages or during the booting stages, a two-shot fungicide application strategy should be considered. A prophylactic two fungicide application strategy should definitely be considered when growing a variety which is very susceptible to blast such as CL151 or CL163.
The best timing for the first application is when the rice is in the boot stage and has a 2- to 4-inch panicle. This 2-shot prophylactic strategy should also be considered for varieties which are susceptible to blast like the new Provisia variety PVL01.
This is especially true for PVL01 since we have to apply more nitrogen to this variety (150 to180 pounds per acre recommended) to maximize its yield potential as compared to most other varieties (120 to 150 pounds per acre).
Sheath blight is another disease we need to scout for and apply a fungicide to manage. Applications of a strobilurin and carboxamide fungicides (Elegia and Sercadis) can be used. However, for if you have strobilurin resistant sheath blight you must use Elegia, Sercadis or the new fungicide Amistar Top.
Applications from the boot stage to 50-70 percent of the panicle emerging from the boot (boot split) are both effective.
Cercospora, kernel smut, and false smut
Cercospora, kernel smut and false smut protection in rice is best achieved with a propiconazole (Tilt, Bumper, PropiMax) fungicide. Propiconazole can also be found in the mixed fungicides such as Quilt, Quilt Xcel, Stratego and Amistar Top. Remember, to control kernel and false smut the fungicide application must be applied before the panicle begins to emerge from the boot (boot split).
The recommended application timing for the smuts is 2- to 4-inch panicle. For Cercospora, application can be made from boot up to heading, with earlier applications recommended when rice is planted late.