By Yeshi Wamishe, Extension rice pathologist
Leaf blast: So far (as of 7/3) in 2018, a total of 10 Arkansas counties have reported blast in rice. These include: Lonoke, Randolph, Poinsett, Pulaski, Lawrence, Greene, Woodruff, Monroe, St Francis, and Clay on Titan, Jupiter Diamond, CL151, Roy J.
The current weather is favorable for diseases—hot and humid. Please continue scouting for blast, especially in fields that have been planted in susceptible varieties. Since maintaining a deep flood depth has been challenging due to the heat with no or limited rain, open fields without a history of blast may show blast if varieties are susceptible. Typically rice blast shows up as diamond-shape lesions often with ashy center, however, early symptoms can be confusing. To learn more on blast symptoms, go to “Recent Disease Update.” To suppress leaf blast from burning down the leaves, fungicides are not often recommended. But raising flood depth to at least 4 inches is recommended and should be maintained throughout the season until draining for harvest.
Sheath blight: Hot and humid weather enhances the progress of sheath blight in rice. Such weather with rain worsens the disease situation. Scouting for sheath blight should start from green ring and go until after heading. Remember, you need to know the threshold before deciding on a fungicide application. Do not make a fungicide application decision based on dense field edges or the bottom of the field. Fungicides are more beneficial in well managed fields. Sheath blight can be severe in fields with high seeding rates that obtained excessive nitrogen fertilizer. Sheath blight progresses both vertically along the plant height and sideways to neighboring plants. Sheath blight can also be more severe in susceptible semi-dwarf medium grain rice than in susceptible, taller, long grain rice. As rice matures make sure the upper two or three leaves are protected from the disease to support adequate grain fill. To read more on sheath blight threshold, scouting technique, and fungicides, go to “Arkansas rice-reproductive-scouting.”
Kernel and false smut: The probability of having severe smut is higher in rice fields with a history of either or both smuts and obtained excessive nitrogen. Scouting for either of these smuts is not easy and not recommended. Therefore, they are suppressed by protective application of triazole fungicide at the correct timing and rate. For more information, go to “A common mistake-Waiting too long.”
Fungicides: Remember the importance of water volume for coverage. To read more, go to “Water volume fungicides.”
Timing for blast suppression: For neck and panicle blast, two applications may be required for maximum suppression with the first at late boot to 10% heading and the second at 50-75% head out. If the necks of the main and secondary tillers are out of the boots, fungicide application is too late. Increase flood depth for early season leaf blast. In cases of leaf burn down, spot treat.
Timing for sheath blight suppression: Boot application followed by heading spray application may be required if cultivar is S or VS; early application is needed if disease starts early followed by PD to boot application. In Arkansas, however, making two applications for sheath blight alone is not profitable.
Timing for kernel and false smut suppression: Timing is narrow and critical. >6 Oz/Acre rate of Tilt equivalent is critical to maximize protection/suppression. Triazole fungicides are applied as protective at the correct timing and rate. For more information go to “A common mistake-waiting too long.”
Fungicides and active ingredients for rice disease management: To see the tables for rice fungicides and their composition go to Rice fungicides.