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Agribusiness: Start weed control early

RESEARCH TRIANGLE PARK, N.C. – Now that rice planting has begin in Texas and Louisiana, can thoughts of weed control be far away? Because practices vary so much across the major rice growing states, university and Extension specialists in Arkansas, Louisiana and Mississippi were asked to provide growers solid advice for controlling weeds and for using a new rice herbicide.

Ricestar HT, which received registration in late 2003, provides superior postemergence control of annual grass weeds in rice, according to Bayer CropScience, the product manufacturer. Ricestar HT will be available in limited quantities for the 2004 growing season.

With a weed control spectrum including barnyardgrass, broadleaf signalgrass, fall panicum and johnsongrass, consistent control of larger weeds up to one tiller is a key benefit of Ricestar HT, company weed scientists say.

“In our greenhouse trials, Ricestar HT was applied at a 17-ounce rate to three-leaf rice,” says Ken Smith, Extension weed control specialist with the University of Arkansas. Smith’s trials used Bengal and Cocodrie varieties, which he explains are more sensitive to herbicides.

“We found that Ricestar HT demonstrated good crop safety under greenhouse conditions. It will be a good tool for rice growers,” he said.

“Get out early, scout early, spray when the weeds are small. Don’t wait for them to get too big,” says Bob Scott, Extension weed specialist with the University of Arkansas in Lonoke, Ark.

A typical weed control program in Arkansas includes the application of a soil-applied herbicide, Command, pre-emergence followed by a postemergence program right before flooding.

Last year, Bayer CropScience issued a 2ee recommendation to tank mix Ricestar herbicide with Command and apply it by aerial application as allowed by the Section 24c special local needs label approved by the state of Arkansas. In 2002, a Section 24c label was granted in Arkansas for aerial application of Command alone.

Recently the state of Mississippi approved a similar label for aerial applications of Command, as well.

“Applying Command by air gives growers more flexibility when it rains as it often does in Arkansas,” says Scott. “Adding a grass herbicide such as Ricestar to Command will add more flexibility because growers will be able to wait a couple of weeks and apply right before flood. Growers will have only one application early season.”

Scott rates Ricestar an 8 or a 9 on most all grasses with 10 being perfect control. “It’s rated really high. I like to see Ricestar go out early. It fits well with Command early post timing because it’s labeled for up to one- to two-leaf grass. I think that’s probably perfect for Ricestar to go out early like that with Command,” recommends Scott.

Command plus Ricestar applications have performed very well in South America, according to Sam Garris, technical service representative with Bayer CropScience.

“We see good potential for a one-shot grass control program with the Command plus Ricestar application,” says Garris.

“Growers need to be walking their fields,” says Joe Street, former rice specialist from the Delta Research and Extension Center in Stoneville, Miss. “They need to identify what they have out there, evaluate their budgets and decide on a weed control program.”

The most troublesome grass last year in Mississippi was barnyardgrass, which is not out of the ordinary.

“We had more of a problem than usual with barnyardgrass last year because the weather was cool early in the season,” says Street. “Our normal applications of propanil did not work well because propanil doesn’t work in cool temperatures. Barnyardgrass got too big for effective control in a number of fields.”

Most rice growers in Mississippi start with applications of Command right after planting. According to Street, Command will last for three to four weeks and that usually doesn’t get a grower to flood. As a result, some barnyardgrass and sprangletop may emerge with the rice, and other grass herbicides are warranted for control.

“Ricestar is better on smaller grass. It’s really good on sprangletop and that’s where it’s found its niche for this part of the country. It’s good on barnyardgrass up to the four-leaf stage. If barnyardgrass gets bigger than that, then you need to add Whip 360 to get the bigger grass,” says Street.

Eric Webster, weed scientist at the LSU Agriculture Center in Baton Rouge, La., says growers need to control grasses when they are smaller.

“Anytime you can get grass when it is small, you need to. It doesn’t matter what grass herbicide you are using,” he says. “What you want to do is control grass when it’s at the two- to three-leaf stage. All grasses, barnyardgrass, broadleaf signalgrass, sprangletop, will be tougher to control when they are at the four-leaf stage and bigger.

“You’re going to get your best control early, plus you’re getting the competition problem out of the way. The longer grass stays in the field, the longer it will impact rice. Ultimately, you will see a reduction in yield,” says Webster.

Barnyardgrass is always a problem in the rice fields of Louisiana, along with sprangletop and now some perennial grasses, according to Webster.

Red rice is also a major concern for growers in that part of the Rice Belt. Because red rice is such a concern, about 90 percent of the rice acres in Louisiana are water-seeded, making weed control practices different from those in neighboring Mississippi.

“We flood our fields prior to planting and then we fly the rice in. Usually the seed is pre-germinated and we let it sit for a day or two. Then, we drain the field and give the rice two to three days to let the root peg into the ground and get a little bit of green foliage. Under an ideal situation, we start bringing the water back into the field slowly, and as the rice starts to elongate, growers keep the tip of the extended leaf just above the water. That’s mainly for red rice control,” explains Webster.

Because the fields are flooded prior to planting and rice is water-seeded, growers look at other grass herbicides later in the season and mainly to control anything that escapes the flood.

“We keep the fields wet so that the red rice seed will not germinate. But we still have problems with grasses, especially sprangletop and barnyardgrass. They will germinate through the flood. Growers need to have a pretty good eye out and they need to know what’s going on with weed pressure in their fields,” says Webster.

Most growers start making their early weed control decisions in the fall when they are harvesting rice. According to Webster, they can evaluate what problems they had the season before. Then, when it’s time to put on the first application at the two- to three-leaf stage, they do it almost blind, meaning that they don’t need to be walking the field at that time because they already know what the problem is.

Webster says the herbicides choices for early grass control are changing. He has noted some resistance with propanil and Facet when it comes to early applications.

“I’m leaning more toward Ricestar early to pick up those grasses at two- to three-leaf stage due to some of the resistance issues we’ve noted. Plus, I know that if I need to tank mix, then I can add a broadleaf compound with Ricestar and not see any antagonism problems. Growers have a lot more options earlier than they do later,” says Webster.

“Make sure your pre-flood applications are timely so when it’s time to flood, you don’t have to come back with any salvage treatments,” says the University of Arkansas’ Scott.

“Identify your weed spectrum up front,” says Street. “Know what your weed is and start your weed control early.”

“Make your applications early,” advises Webster. “If you can see the weed, a lot of times it’s too late. Don’t be afraid to use your water. I think it’s just as important as it used to be.”

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