Varieties have been selected, and the rice crop has been planted. So, two of the most important rice disease cultural management practices, planting early and using resistant or less susceptible varieties, are complete.
Points that you still need to consider are to establish and maintain the permanent flood to suppress blast, do not over fertilize with nitrogen, know which varieties are susceptible or very susceptible to blast, sheath blight, and Cercospora, keep a close eye on them for disease development, keep track of rice growth stages so fungicide applications can be done correctly, and have a fungicide resistance prevention plan.
The primary diseases that fungicides are used for include sheath blight, blast, Cercospora, and the grain smuts. Fungicide trials have been conducted at the Rice Research Station since the early 1980s. The studies demonstrated that fungicide selection was important in sheath blight, blast, and Cercospora control.
Effective fungicide use must be based on the presence of the most damaging disease in a field. This is determined by knowing the varietal susceptibility, field disease history, weather conditions in your area, and, most importantly, by scouting for disease in the field multiple times during the growing season.
Propiconazole-containing fungicides – Tilt, PropiMax, Bumper, Stratego, Quilt, and Quilt Xcel – were most effective against Cercospora and kernel smut. But Tilt, PropiMax, and Bumper were very weak against sheath blight and have no activity against blast when used alone. Based on research from Arkansas, propiconazole is most effective against kernel smut and some activity against false smut.
Application at the mid- to late-boot stage is most effective. The strobilurin fungicides have activity against both sheath blight and blast. Azoxystrobin-containing fungicides – Quadris, Quilt, and Quilt Xcel – were more effective against sheath blight than the trifloxystrobin-containing fungicides, Gem and Stratego.
But the trifloxystrobin-containing fungicides were somewhat more effective against blast. The SDHI fungicides, Sercadis and Elegia, are effective against sheath blight including the strobilurin-resistant sheath blight pathogen. Sercadis has some Cercospora activity.
If the strobilurin-resistant Rhizoctonia solani is present in the field, Sercadis or Elegia must be used to control sheath blight; however, these fungicides have no activity against blast. Reports of SDHI resistance in the sheath blight pathogen population are not substantiated at this time.
A new fungicide, Amistar Top, may be available late this year for rice. It contains both azoxystrobin and difenoconazole and will add to our fungicide resistance arsenal. It has sheath blight, blast, and Cercospora activity when applied at the correct growth stage.
Multiple fungicide applications may be necessary to manage multiple diseases in a field because of selective activity, disease severity, and label restrictions.
There are limitations on fungicide application timings. You must read and follow the label. Also, check fungicide prices to determine the most cost-effective program. For additional information and current disease control options, contact your local LSU AgCenter extension agent for information and advice.