Planning Your 2020 Fungicide Program For Rice

By Donald Groth, Ph.D.

LSU AgCenter

The primary diseases we use fungicides for include sheath blight, blast, Cercospora, and the grain smuts.

Fungicide trials have been conducted at the H. Rouse Caffey Rice Research Station since the early 1980s. Various fungicides and fungicide combinations were applied at different growth stages, ranging from seven days after panicle differentiation to 50 to 70 percent heading. Varieties selected were susceptible to sheath blight, blast, or Cercospora and were managed to favor disease, i.e. inoculated, fertilized with high N rates, planted late, and/or planted in high disease pressure fields.

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- and Difenoconazole-containing fungicides – Tilt, PropiMax, Bumper, Stratego, Quilt, Quilt Xcel, and Amistar Top – were most effective against Cercospora. But Tilt, PropiMax, and Bumper were very weak against sheath blight and had no activity against blast when used alone (See Table 1). The strobilurin fungicides had activity against both sheath blight and blast.

Azoxystrobin-containing fungicides – Quadris, Quilt, Quilt Xcel, and Amistar Top – were more effective against the wild type sheath blight than the Trifloxystrobin-containing fungicides, Gem and Stratego. But, the Trifloxystrobin-containing fungicides were somewhat more effective against blast. If the strobilurin-resistant Rhizoctonia solani is present in the field, Elegia, Sercadis, and Amistar Top must be used to control sheath blight; however, Group 7 fungicides have no activity against blast.

Based on research from Arkansas, propiconazole is most effective against kernel smut and some activity against false smut. Application at mid-boot is most effective. 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 Cooperative Extension agent.