Rice water weevils pose problems

Rice water weevils are tormenting Mid-South rice producers and causing many to rue the recent loss of several controlling products.

“Some growers had water weevils sneak up on them this year,” says Glenn Studebaker, an Arkansas Extension entomologist who spoke at an IPM meeting in Haynes, Ark., on June 15. “I've had a lot of calls on those (since the beginning of June).

“Regularly I hear, ‘I had my rice flooded for two weeks. I just went out and had a look and have scars on every plant. I pulled some and there are larvae on the roots. What do I do?’

“There's no answer producers will like. The only thing that can be done is drain the field. You have to almost dry it all the way to kill the larvae.

“We need to scout rice fields heavily the first week of flood. After that, you've lost the chance to spray adults before they lay eggs.”

In Louisiana, the rice crop is further along, but it too has had intense weevil pressure. For the most part, Johnny Saichuk's verification fields are past treatment stages.

The LSU AgCenter rice specialist suspects the majority of acreage at threshold has been treated or should have been.

“It's probably too late to treat now,” says Saichuk. “The really big problem is we have no larvacide to deal with weevils in the roots. If you miss the adults, draining is all you can do. Most of our rice is beyond that stage, by now.

“Pyrethroids are fine but we…need a larvacide badly. Until we (have one), we will run into situations where we believe the weevils have been controlled and then find out the roots are full of them. That means we missed a flight.”

Until recently, water weevils were a secondary concern — particularly for producers using Icon.

“This is life without Icon,” says Chuck Wilson, Arkansas Extension rice specialist. “Rice water weevils are eating our lunch. And this is widespread.

“Water-seeded fields are really being hurt by weevils. But I've been in drill-seeded rice where weevils have pruned off all the roots and the crop is barely hanging on.”

Adult weevils can be controlled with pyrethroids. Those must be applied pre-flood or up to a week post-flood. Miss that window and the weevils will have laid their eggs. Once the eggs hatch and larvae are out, the crop is in trouble as there's no chemical control.

At that point, draining and drying the field is the only control option.

Unfortunately, many producers haven't the water capacity to drain and flood again.

“If they drain and dry the field, they'll never catch up with the water,” says Wilson. “That's presenting problems.”

At the same time, the rice crop is moving fairly rapidly. Many farmers have had to delay the flood to try and get the crop healthy. Two weeks after flood there are already fields with moving joints.

“In that situation, it's a tough call on whether to drain a field. I like to have the flood back on the field when the joints start moving.”

Over the years, some growers have put out mid-season fertilizer to try and help plants recover. That can be a Catch-22, warns Wilson.

“You've got to have roots to take up fertilizer, but you also need fertilizer to encourage root growth. I wouldn't expect a lot of benefit from adding fertilizer. But sometimes that may lead to some extra root growth.”

The Mississippi rice crop, which looks good overall, has also seen its fair share of weevils.

“We had some thin stands, so a lot of pyrethroids were put out either pre-flood or a week after flood,” says Nathan Buehring, Mississippi Extension rice specialist. “We went with more of a preventive approach.”

However, there have been some cases where second shots of pyrethroids were needed. “Those we put out near flooding and then 10 days later — after live adults were found in the field. Without Icon — and especially Furadan — there aren't a lot of options.

The early Mississippi rice crop — planted before April 15 — looks great.

“We haven't had major problems with it. We had great weather right out of the gate. There was some 90-degree weather in April. The rice jumped out to good stands. But shortly after that, the weather got cold and wet and the crop slowed down. It picked back up a couple of weeks later.”

Mississippi has a wide range in crop maturity. “We've got a quarter to a third of our crop past mid-season. Then, we've got rice at the two-leaf stage.

“We had some major troubles with glyphosate drift in mid-May. That was a big issue in the state. We probably replanted 15,000 acres. Whether that went back to rice or soybeans depended on the situation.”

Another 20,000-plus acres of rice was at least “somewhat affected” by glyphosate drift. “It was a headache whether that was a bit of stunted growth that needed a flush and fertilizer to get going, or other symptoms that set back acreage.”

Following hurricanes and drought, Louisiana's rice acreage took a hit this year.

“We've done some unofficial estimates and it appears we're at 65 to 68 percent of last year's acreage,” says Saichuk. “That puts us at about 360,000 acres.”

The Louisiana crop in the field “looks decent. It won't be a record with this dry weather. But the dry weather holds a positive — there's been very little disease pressure.

“Of course, a big negative is the higher pumping costs. A farmer called me and said he was up to $60 per acre just on pumping. This is an expensive crop. We do usually make higher yields the more we pump.”

Wilson says recent problems with Clearfield hybrids (see http://deltafarmpress.com/news/060706-Clearfield-rice/index.html) appear to be lessening. “The ones I've seen are looking a little better. In some cases, the stand remains thin.

“To me, what was different this year than in the past was how widespread the problems with those hybrids were. Another thing that was different is a lot more of it was killed. Last year, we saw injury and sick hybrids. But the flood and fertilizer helped it grow out of the trouble. Hopefully, we can figure out what to do to keep from revisiting this.”

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