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.

Wilted stalks of rice with black spores indicating kernel smut infection
Rice infected with kernel smut may not show symptoms early on, but will contain black fungal spores at maturity. (Young-Ki Jo/Texas A&M AgriLife)

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.

AgriLife Extension’s response to rice disease

People sit and stand on a trailer in a field listening to a scientist from AgriLife Research
Rice field days offer producers the chance to hear from experts within AgriLife Extension and AgriLife Research. (Michael Miller/Texas A&M AgriLife)

Beginning in July, Jo said AgriLife Extension’s county agent rice team will begin its annual field surveillance to collect data across Texas rice growing regions on disease severity and any additional issues.

“We collect data throughout the summer and compile it to determine how to best respond to rice disease issues,” he said. “We’re going to have new information, which allows us to update and improve our recommendations every year.”

Jo said the rice team also coordinates and shares their findings with rice researchers at the Texas A&M AgriLife Research and Extension Center at Beaumont, who are working to develop disease-resistant cultivars and better management practices. Producers can attend the Eagle Lake Rice Field Day on June 25 and the 76th annual Beaumont Rice Field Day on July 11 to tour the research stations and hear from experts about rice breeding, plant physiology, and insect, weed and disease management.

“Our AgriLife Extension rice team is trying to facilitate more coordinated efforts to support the Texas rice industry,” Jo said. “The major goal is to keep a tight relationship between county agents, specialists, rice researchers and Texas rice growers.”

For more information on disease management recommendations, visit the Department of Plant Pathology and Microbiology’s AgriLife Extension site or contact Jo and Sam Rustom, Ph.D., AgriLife Extension rice specialist.

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