Wet conditions help pathogens gain ground in rice fields.

Raney Rapp, Senior Staff Writer, Delta Farm Press

At a Glance

• Moderate temperature, high moisture perfect for rice diseases.
• Some hybrids and other varieties are susceptible to cercospora.

Perhaps the most ‘normal’ weather for farmers is the lack of any sort of ‘normal’ weather at all. Every year brings unique challenges and for rice farmers throughout the midsouth wet conditions are pulling pathogens to the forefront of management decisions.  

“This year is it’s been raining almost every day for multiple weeks, but the difference on this year than the year before is that the temperatures are now more moderate than they were,” said Felipe Dalla Lana, Louisiana State University Extension rice pathologist. “This year, temperatures are about 80 to 82 where last year and the year before they were usually 95 to 100 – much more hot than it is right now.” 

At the H. Rouse Caffey Rice Station in Crowley, conditions are proving to be a good proving ground for disease resistance and control, as well as a barometer for surrounding producers facing the challenges of a wet, cool start to the growing season. 

“At temperatures above 100, you have no concerns about those disease, but at 80 with a lot of moisture, that’s just the perfect conditions for most of diseases,” Lana said. “The weather is being very conducive for disease and we are starting to see those effects in the field right now.” 

Sheath Blight 

Sheath blight is a pathogen dependent on inoculum in the soil from previous seasons. At the Crowley Station, Lana said plots have seen minimal sign of sheath blight because the plots planted in rice this year, were also in rice in 2023, a hot, dry year where much of the inoculum needed for sheath blight did not survive.  

“We expect to see a lot of variation in sheath blight from field to field,” Lana said. “Where we planted this year in 2025 we also planted in 2023. That was a very hot and dry year, so we did not have that much inoculum building in the soil and sheaths blight is a soil borne disease.” 

Lana said farmers growing rice with a crawfish rotation potentially also have less inoculum accumulated in the soil, but farms with a soybean rotation likely have more. Sheath blight risk revolves around the availability of the pathogen in the soil and specific on-farm conditions, so it’s important to scout and assess the individual risk of each field.  

“Even though we have a very good weather, a lot of fields don’t have as much inoculum in the field. So we expect to see much more variation field to field,” Lana said. “It’s hard to say if this is a bad season for sheath blight or it’s not. It depends from field to field and farm to farm.” 

What to look for:  

• Large oval spots on the leaf 
• Spots on the leaf blades 

Cercospora  

“For cercospora, 2022 and 2024 were the years that we have more concerns on cercospora, and more problems with cercospora,” Lana said. “What happened those years? We had a lot of rain, a lot of moisture after heading and after flowering.” 

For cercospora concerns, Lana said the weather through the month of July would determine how challenging conditions would get. If wet weather continues through heading and flowering, farmers could begin to see more cercospora problems.  

Louisiana isn’t the only region with cercospora concerns for 2025, University of Arkansas rice pathologist Camila Nicolli said farms in her region could also see instances of the disease.  

“Although it is a big problem in Louisiana, we also have cercospora problems in Arkansas,” Nicolli said. “There are some hybrids and some other varieties that are susceptible to cercospora, so it’s good to check recommendations.” 

What to look for:  

• Linear brown lesions on leaves 

• Lesions with tan centers and brown borders The H. Rouse Caffey Rice Research Station during LSU’s 116th annual field day at the Crowley location. (Raney Rapp)

Rice Blast  

While rice blast is not a problem pathogen for growers every season, it is a pathogen with potentially devastating effects, especially in wet conditions.  

“Blast is a disease that I personally have a deep respect for,” Lana said. “In a bad season of sheath blight, you might lose 30% of your yield, but in a bad season of blast, it can destroy your whole yield.” 

Typically blast is not a major concern because of varietal resistance, Lana said. Reports of blast cases in varieties like LSU’s Titan, are a cause for concern for the coming season. 

“In terms of blast, most of our varieties are resistant,” Lana said. “We have a lot of options. The varieties are very stable. But we still have some varieties that have susceptible to glass, and the weather that we have right now is just perfect for blast.” 

Arkansas as well has already had a case of blast reported, Nicolli said.  

“For a long time, we hadn’t seen too much blast in Arkansas, and last year I visited 22 fields that was positive for blast,” Nicolli said. “What I want to say is to check the weather.”  

In many cases, Nicoli said blast will appear about 7 days after a heavy dew. After hearing reports of a morning with the right conditions, she had her first report of the disease a week later. 

“On my way home, I will collect the first report of blast in Arkansas,” Nicolli said. “The weather is right, the inoculant is there, so the pathogen is present. Sometimes what we need is just the susceptible variety and the weather, and then we can see some of these diseases.” 

What to look for:  

• Diamond shaped leaf lesions with a white center and brown border 

• Infection of the panicle 

Published Date: July 17, 2025