Like most of the Midsouth, Louisiana has seen an abundance of rain this year, setting rice producers up for high disease pressure. Growers have reported high incidence of sheath blight due to seemingly constant rain and high humidity.

Sheath blight, one of the most prevalent diseases in Louisiana rice, is caused by a soilborne fungus that also infects soybean. In areas where rice and soybean are rotated, disease pressure is increased.

Trey Price, associate professor in LSU’s Department of Plant Pathology and Crop Physiology, discussed best management practices for rice disease at the recent Rice Field Day. Price recommended an application of fungicides containing a strobilurin, SDHI, or difenoconazole from boot to heading to manage sheath blight. If disease initiates earlier, applications may be warranted.

“Resistance to strobliurin fungicides has been documented in areas of south Louisiana,” Price said. “In areas where resistance is suspected, applications of Elegia, Sercadis, Amistar top or Artisan are recommended. Some varieties/hybrids have a degree of resistance to sheath blight. However, under conditions favorable for disease resistance, fungicide application may be necessary, even in resistant varieties.”

Other rice pests

The rice water weevil remains the most damaging pest of U.S. rice. Larvae feed on roots and can reduce yields by 20% or more if not managed. Weevils are effectively managed with insecticidal seed treatment.

“Of the products currently offered, Dermacor X-100 is the most effective available seed treatment for weevil control. This product also controls armyworms and stem borers,” said Blake Wilson, assistant professor with field crops entomology with the LSU AgCenter. “The seed treatment Fortenza received a registration for rice in 2019. This treatment is as effective against weevils as Dermacor X-100 when used in combination with CruiserMaxx.”

Alternative management strategies to prevent the development of insecticide resistance to seed treatments include delayed flooding. Wilson said delaying establishment of permanent flood allows for the growth of a robust root system before infestation occurs, reducing yield loss.

New emerging rice pests include invasive apple snails. Pink globular egg masses are easy to see. Apple snails can reach much larger sizes (apple-sized) than native species and lay easy-to-spot bright pink egg masses above the water surface. The impacts of snails on drill-seeded rice are minimal, but stands of germinating rice can be greatly reduced in water-seeded fields. Crawfish production has been severely impacted in some areas as high populations of snails clog traps and disrupt fishing. Current research efforts are monitoring expansion of the snails and investigating chemical controls which are compatible with crawfish production.

Another emerging pest is billbugs infesting furrow-irrigated rice (row rice). The removal of the permanent flood exposes rice to new insects that are not problematic in aquatic systems. Billbug larvae feed inside stems at the base of the plants near the soil surface. This feeding produces a whitehead similar to those caused by stem borers. Yield loss approaching 20% has been observed from billbugs in row rice in northeast Louisiana. Insecticidal seed treatments are not effective, and current research is aiming to identify effective foliar insecticide strategies.