Good Offense Is Good Defense Against Pests

Boris A. Castro, Webster, Eric P., Schultz, Bruce, Saichuk, John K.  |  4/22/2005 6:18:18 PM

Eric Webster

News Release Distributed 04/20/04

ABBEVILLE – A good offense is a good defense in the game against pests, LSU AgCenter experts told rice farmers and agricultural company representatives last week.

Weed and insect specialists from the LSU AgCenter met Friday (April 16) at the Cecil McCrory Exhibit Hall in Abbeville to field questions from farmers and others and to give advice. They recommended a proactive approach.

Dr. Eric Webster, an LSU AgCenter weed scientist, reminded farmers that the Newpath herbicide, made to use with herbicide-resistant Clearfield rice, kills red rice and other grasses but not broadleaf weeds – although it will affect broadleafs before they emerge.

"I like to get my first treatment on early," Webster said.

Clearfield is expected to be planted on almost a fifth of the 530,000 rice acreage anticipated for Louisiana.

Webster said the second Newpath application should be 10-14 days later.

Webster said an application before and after flooding is best – with the second application made prior to permanent flood establishment. He urged against using the entire Newpath application prior to a permanent flooding.

The LSU AgCenter expert cautioned the recommended rate of 4 ounces per acre should be followed closely and said he’s convinced using less than the recommended amount is false economy.

"When you start cutting rates, you buy yourself another application," he said.

The active chemicals in Newpath bind to the soil, and if fields are allowed to dry, the chemicals are less likely to re-activate when moisture returns, Webster explained.

In addition, Newpath is active only when a plant is growing, so the cold weather affects the chemical’s effectiveness, he said, and many weeds stop growth at 50 degrees.

Weeds should be sprayed before they reach the 4-leaf stage; otherwise farmers will be facing an uphill battle, Webster said.

The LSU AgCenter scientist recommended keeping fields moist to help prevent red rice from germinating.

He said he favors the use of water to control red rice instead of allowing red rice to germinate and grow before spraying with Newpath. Practically speaking, he said, no herbicide has a 100-percent kill rate.

In other news, Dr. Boris Castro, an LSU AgCenter entomologist, warned that the rice water weevil is the main insect pest farmers should be concerned with now.

The weevils are emerging from their winter homes in woodlands and they are flying to fields as soon as their wings fully develop, Castro said. Once in the fields, the insects will feed on rice plants, mate and lay eggs in rice leaves just above or below the waterline, he explained.

It’s the larvae from those eggs that do the damage, chewing on rice plant roots, Castro said.

Once established, adult weevils will lose their ability to fly, because their wings essentially degenerate, or at least lose the ability to function, he said. Recent cold weather won’t make them leave the fields either, he said.

"If rice water weevils were already established in your field, they are not going anywhere else," Castro said.

Feeding scars will indicate the adults’ presence, Castro said, and locating a few of the hard-to-find insects will confirm suspicions of a larger population.

"If you see one, there probably is more than one, because they typically arrive in waves of many adults," Castro said.

A degree-day model being developed by the LSU AgCenter has predicted weevils will first migrate in early April, followed by a larger mass migration three weeks later, Castro said.

That particular model applies to the Crowley area only, however, so different rice fields may have conditions that either encourage or delay the arrival of weevil adults, the expert explained. Therefore, rice fields must be monitored for this insect, he said.

It’s important to spray insecticide after finding adults or feeding scars, Castro said, because the only pesticides authorized now for use after planting are for adults only. Once eggs are laid and hatch about a week later, there isn’t any chemical control against the larvae, Castro pointed out.

The pesticide Dimilin, which targets eggs, is too expensive, and draining field to reduce larval populations is not always effective and may bring additional costs, he said.

In addition, the seed treatment Icon is no longer being made, and available stocks are being used up. The pyrethroid insecticides Mustang Max and Karate are on the market to kill adult weevils, and two more similar products, Proaxis and Prolex, are expected to be available in May. All four chemicals are sprayed on the affected plants to kill adult weevils both by contact and ingestion.

Castro said he’s worried that pyrethroid chemicals are the only type of agent available for farmers, because the possibility exists that insects will become resistant to those materials.

Since one female can lay 200 to 400 eggs, and just one larva will reduce yield by 1.3 percent, Castro stressed a major infestation could cost farmers as much as $91 an acre from yield losses.

Rice specialist Johnny Saichuk of the LSU AgCenter said a verification field in Allen Parish had to be sprayed twice for weevils, but that is the exception.

Castro advised spraying as early as 24 hours before flooding also is an option, and he said it best to spray when the first weevils are found in a field, and when water is or will soon be present in the field.

A mass adult migration typically occurs soon after water is present and rice plants have emerged, according to the experts. In addition, pyrethroids generally are effective only four days to five days after spraying, so fields must be scouted again for additional weevil arrivals five to seven days later, Castro said.

Contacts: 
            Boris Castro at (225) 578-7386 or bcastro@agcenter.lsu.edu
            Johnny Saichuk at (337) 788-7547 or jsaichuk@agcenter.lsu.edu
            Eric Webster at (225) 578-5976 or ewebster@agcenter.lsu.edu
Writer: 
            Bruce Schultz at (337) 788-8821 or bschultz@agcenter.lsu.edu

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