Tiny Pest Hits Rice; Scientists Think Insect Is New Species

Boris A. Castro, Schultz, Bruce  |  4/28/2005 1:21:31 AM

News Release Distributed 01/27/05

What critter has no name, eats rice plants and has the potential to make farmers see red?

The answer, according to Dr. Boris Castro, LSU AgCenter entomologist, is a tiny fly.

"The way it looks, it probably is a new species for the U.S.," Castro said of the pest discovered in a number of rice fields last year.

And Howard Cormier, LSU AgCenter county agent in Vermilion Parish, said the insect’s damage was devastating on two fields he inspected last year.

"Where it hit fields, the rice never did come back," Cormier said.

Farmer Ted Girouard of Kaplan had one of those fields. "It just demolished the rice," he said.

Girouard said he lost 51 acres of rice to the pest, and his remaining 130 acres yielded a paltry 12 barrels an acre.

Castro said the pest has so far been referred to as the rice whorl maggot because of its similarity to a fly in Asia that afflicts rice fields there. But he said a taxonomist at the Smithsonian Institution has concluded this fly probably is a new, unidentified species in the United States, although it could be a species originating from Costa Rica that hasn’t been named.

Oriental rice fields also are damaged by the Asian rice whorl maggot, Castro said, so it may be necessary to distinguish the fly in U.S. rice fields as the American rice whorl maggot.

Whatever the insect is, it has infested rice fields in Vermilion, Jefferson Davis, St. Landry and Concordia parishes, Castro said, and Dr. Mo Way, Texas A&M entomologist, has found it in Texas rice fields on a smaller scale.

Castro said he inspected seven fields in 2004 that had severe infestations – where large areas were denuded of vegetation, but he suspects it affects more fields to a lesser extent.

"Probably this insect is in more fields than we think it is," Castro said.

For the past few years, he said, it was believed the damage was caused by another small fly called a rice leaf miner, also a major pest in Asia. "Here, we consider the rice leaf miner a secondary pest," Castro said.

While a leaf miner produces larvae that burrow between the two layers of a plant’s leaf, Castro said the larvae of this newer pest, which is an eighth of an inch to a quarter-inch long, feeds on a leaf’s edge and works its way down into the whorl of a seedling where a plant’s leaves and stem emerge. It’s not unusual to find several larvae infesting one plant, he said.

Damage is severe, either killing the plant or retarding growth, Castro said.

Girouard said the problem in his field developed two weeks after planting last year. He said he first thought the problem of yellowing leaves was the result of bronzing, a mineral deficiency, and he released the water from the fields.

Girouard then replanted 51 acres, but the problem returned, and he gave up on that field.

"It’s the first time I ever lost a crop," he said.

In the fields where plants reached maturity, Girouard said the plant density was so thin that weeds overwhelmed the surviving rice.

The insects’ effect on yields is significant, Castro said, but research will have to be done this year to determine the range of damage.

It also will be important to find out the early signs of infestation, the LSU AgCenter entomologist stressed. By the time a plant shows obvious signs of dead leaves, it is too late to use any chemicals. And so far no insecticides are labeled for use against the pest, Castro said.

Castro said LSU AgCenter research this year also will include spraying different insecticides, which are already labeled for other rice pests, on test plots where the insect is found.

The fly doesn’t seem to have a preference of varieties or seeding methods, Castro said, but late planting appears to be a common thread. It usually struck in June and July, he said, explaining the first case was found in a field that was planted in May.

"The earlier you plant, the better," Castro said.

The LSU AgCenter recommends planting rice between March 15 and April 20 in South Louisiana, and the recommendation for North Louisiana calls for planting between April 5 and May 10.

Girouard said he usually plants in March or April, but he was delayed until July because he had difficuly getting a dependable well.

"I’ll never plant late rice again," he vowed.


Contact:     Boris Castro at (225) 578-7386 or bcastro@agcenter.lsu.edu
Writer:        Bruce Schultz at (337) 788-8821 or bschultz@agcenter.lsu.edu

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