Prevention Of Kernel Smut Disease In Rice Harvest

ASHLEY VARGO

COLLEGE STATION, TEXAS

Over the last several years, rice kernel smut disease has transformed from a low-grade issue to a challenge for rice

growers in Texas and other U.S. Rice Belt regions, according to experts.

Young-Ki Jo, Ph.D., Texas A&M AgriLife Extension Service specialist and professor in the Texas A&M College of Agriculture and Life Sciences Department of Plant Pathology and Microbiology, said kernel smut has become increasingly problematic for Southern U.S. rice producers. Concerns about rice kernel smut disease culminated with an outbreak in 2021 that led to a significant reduction in rice quality and quantity for Texas growers.

“Things are changing in the rice industry,” Jo said. “Every year, we have a new threat – too much or too little water, triple-digit temperatures during sensitive growth stages. Those factors are always going to affect plant health, but emerging diseases and pests are causing additional problems alongside extreme weather.

“Kernel smut disease has been around for a long time, but only recently has it started to raise major concerns in rice production in Texas. Especially with the frequent rain this season, growers need to act now to limit the risk of a disease outbreak during the first crop harvest.”

What causes kernel smut disease

Kernel smut disease is an infection of the endosperm in rice kernels by the fungus Tilltia horrida. Jo said kernel smut spores disperse by wind and water and can remain in the soil for longer than three years. The resilience of the spores increases the likelihood of repeated outbreaks in the same fields.

The initial infection of the fungus on rice plants is unnoticeable and does not affect the plant growth, Jo said. Infected kernels look normal at the early stage. However, at maturity, infected kernels are filled with a black sooty powder — the fungal spores, called teliospores. In addition to reducing yields, the infection can result in price reductions at mills or even outright rejection of rice grains contaminated with black spores.

“One of the challenges in controlling kernel smut disease is the early diagnostics,” Jo said. “There aren’t any lesions or symptoms on the leaves, the grain looks fine, and then suddenly when it matures, the infected grain is full of black spores. We don’t always know when the fungus starts to infect the plant, but we know the fungus must enter flowers to complete its disease cycle.”

Kernel smut prevention strategies

There are no fully disease-resistant rice cultivars or silver-bullet treatment methods for kernel smut, which means disease management must be preventive, using fungicides.

“Since early diagnosis is very difficult, if not impossible, we will have to use fungicide proactively to control the disease,” he said. “Growers should treat with fungicide in the early stages and may need to perform multiple applications before or immediately after panicle emergence.”

Jo recommends using fungicides with newer triazole ingredients, such as difenoconazole at the mid-boot stage, and applying a second round of fungicides within a 14-day interval when the weather condition is favorable for fungal infection, like this year.

Additionally, planting early and using hybrid rice varieties, which are known to be generally less susceptible to diseases, can help in reducing disease occurrence.   ∆

ASHLEY VARGO: Texas A&M University