Minor diseases... major problems

LITTLE ROCK — Most heading diseases of rice are considered minor compared to blast and sheath blight, but in some areas of Arkansas they’re more than a nuisance or scientific curiosity.

In Poinsett County, for instance, bacterial panicle blight has become a serious threat to the county’s 60,000 acres of Bengal, a high-yielding, medium-grain rice variety.

Another heading disease is a threat to some of the long-grain varieties. “In some long-grain varieties, especially LaGrue and Francis, kernel smut can cost farmers yields and quality, hitting them hard in the pocket book,” says Mike Hamilton, county agent with the University of Arkansas Cooperative Extension Service.

“Kernel smut was not as bad in 2003 because farmers applied fungicides,” Hamilton says. In areas of the county where farmers did not use preventative fungicides, combines turned black at harvest from black fungus spores.

Rick Cartwright, Extension plant pathologist, says heading diseases show up late in the season unexpectedly and often too late to do anything about it. Heading diseases of rice causing problems include neck blast, kernel smut, false smut and bacterial panicle blight. They can substantially affect yield or quality, or both.

While traditionally considered a minor concern, these diseases have become major problems for some growers under the right environmental conditions on new, higher-yielding rice varieties.

Cartwright began studying heading diseases a couple of years ago with help from the Arkansas Rice Research and Promotion Board. Fleet Lee at the Rice Research and Extension Center at Stuttgart, Ark., already had a research project studying the most important heading disease — neck blast.

Cartwright initially worked with chemical control methods. He found that fungicides such as Tilt, Propimax and Stratego were effective in preventing kernel smut and suppressing false smut, if applied at the correct time.

This board-sponsored research led to current university recommendations for using these fungicides to help manage the smut diseases and improve rice quality at harvest.

Meanwhile, Cartwright says researchers at UA and LSU have been testing experimental chemicals that are effective against bacterial panicle blight.

“We’ve also found that fungicides such as Quadris, in certain instances, seem to help Bengal rice affected by bacterial panicle blight. While this material doesn’t have a direct effect on the disease, it seems to help preserve yield and quality.

“We’ve measured yield losses from bacterial panicle blight of up to 30 percent. It has turned the very high yielding Bengal variety into just average,” says Cartwright.

More recently, the heading disease program has enlisted the help of other scientists and researchers.

“Nathan Slaton at Fayetteville, Ark., is studying the effect of nitrogen fertilizer on smut diseases. He has found that pre-flood nitrogen rate mostly affects the severity of the diseases. We had always assumed the mid-season nitrogen applications were more important.

Cartwright says David TeBeest at Fayetteville and Lee at Stuttgart are trying to determine how various heading diseases survive from crop to crop in the seed and whether they can be controlled with seed treatments.

Yiyong Yang in the Department of Plant Pathology is trying to determine how to detect bacterial panicle blight in seed. “We’ll have a sampling and detection method soon,” says Cartwright.

Yang is also looking at biotechnology to make plants more resistant to bacterial panicle blight. Conventional resistance to the disease has not been easy to find in rice varieties grown in the southern United States.

Meanwhile, Cartwright is screening various rice lines in the field, mainly at the Pine Tree Station, for susceptibility to heading diseases.

“As new varieties get close to release, we want to make sure we don’t get surprised by their reaction to heading and other rice diseases.”

Lamar James is an Extension communications specialist with the University of Arkansas.