Over the past 10 days, we have seen a lot of rain across the state, and if it was not raining, it was humid and overcast. These are perfect conditions for the development of sheath blight.
With the increase in the apperance of sheath blight over the past week, Dr. Don Groth, rice pathologist, has provided a sheath blight disease update and management section below. The incidence of blast, however, has remained low thus far in southwest Louisiana.
Rice Disease Update
Severe sheath blight (see photo above) has been reported in several fields, mostly CL111, moving upward very rapidly, but it is hard to detect in other fields. Some hybrids have had treatable levels of sheath blight. The current weather patterns (warm and moist) favor continued sheath blight development. As the rice approaches reproductive stages, sheath blight development will increase. A few fields have already started to head.
Remember, fungicides need to be applied by 50-70% boot split (early heading)! Some blast has been found mostly on Jupiter but other susceptible varieties may be affected. I would still plan on spraying a blast fungicide on very susceptible varieties at heading. This later application should still have good sheath blight activity.
A little Cercospora has been reported especially on CL111, which is the most widely grown variety this year. The longer a variety has been released and the more common it becomes, diseases tend to become more severe. We are recommending 9-12 oz per acre of propiconazole to control Cercospora. This is higher than previously recommended, but the pathogen is starting to become tolerant of the fungicide.
Temperatures remain hot but not excessively high (95o F and above) so damage from bacterial panicle blight will hopefully remain light. T
he strobilurin-resistant sheath blight fungus continues to spread, so we need to rotate fungicide chemistry in our rice and soybean fields. Sercadis and Elegia fungicides provide much better sheath blight control in fields where the strobilurin-resistant sheath blight fungus is present than the strobilurin-containing fungicides Quadris, Quilt, Stratego and Gem.