Pathologist: Less disease pressure seen on 2020 crop

The 2020 Louisiana rice crop suffered less disease than the previous year, said Don Groth, LSU AgCenter plant pathologist.

“Disease pressure was not severe, and we saw much less grain smut compared to last year,” Groth said. “This could be due to less favorable environmental conditions in 2020 and the timely application of smut-effective fungicides that were applied to a large percentage of rice fields.”

He said false smut was present in research plots that were not sprayed.

“We planted late due to COVID-19, but nurseries and plots turned out very uniform,” Groth said. “In our disease ratings for Louisiana breeding materials, we saw blast disease ratings from 0 (immune) to 9 (very susceptible).”

Groth said bacterial panicle blight ratings ranged from 2 to 8. He said resistance to bacterial panicle blight is available in the populations that rice breeder Adam Famoso is working with.

He said his plots inoculated with sheath blight had ratings that ranged from 4 to 8.

“What is important is the lines with a sheath blight rating of very susceptible that were common in older varieties and germplasm have been virtually eliminated, and a significant number of moderately susceptible to resistant lines have become common in the breeding populations,” Groth said. “These lines will not require fungicide applications except under very favorable environmental and cultural conditions.”

The bacterial panicle blight resistant lines will not have enough damage to be detected in yield reductions like current susceptible and very susceptible varieties except under hot conditions.

He said a new fungicide, Excalia, appeared to be promising at controlling fungicide-resistant sheath blight fungus in a trial conducted in Calcasieu Parish. “Unfortunately, yield and milling data were confounded or even lost to Hurricane Laura,” Groth said.

Groth said the product has been effective at very low rates of 2 to 3 ounces per acre in previous years.

Fewer fungicides are being tested for rice, he said, “but gains in genetic screening and breeding should help greatly in the near future.”

Groth also said smut fungicide trials showed a striking difference between plots that were sprayed and those that were not treated.

“It was some of the best trials I’ve ever had,” he said. “A night and day difference.”

He said products with propiconazole at 6 to 10 ounces per acre or difenoconazole, one of the active ingredients in Amistar Top, were effective.

Disease workJPG

Resident coordinator of the H. Rouse Caffey Rice Research Station Don Groth, at right, conducts disease ratings for different varieties in his plots while Caitlyn DeNux, research associate, records his observations. Groth is retiring at the end of January at the end of almost 38 years as a plant pathologist.

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Don Groth holds a rice panicle infected with false smut disease from one of his test plots that showed the benefits of fungicides to treat the problem. In 2019, farmers reported problems with kernel and false smuts but few farmers had that problem in 2020.

11/24/2020 9:58:58 PM
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