Clearfield rice offers potential, concern

Red rice frustrates rice growers all over the Delta. To help combat the plant, BASF recently introduced Clearfield rice. The rice varieties offered under the Clearfield system are herbicide-tolerant and thus make controlling red rice much easier. The new technology works well, but isn't foolproof and there are several things to watch for, says Tomilea Baldwin of Practical Weed Consultants.

Currently, there are two Clearfield varieties available: CL 121 and CL 141. They're both good varieties, says Baldwin, but they can't tolerate two applications post-emergence.

“Normal varieties don't have that problem. For example, you can come early with a post-emergence propanil treatment and come back with a second treatment to get the weeds you missed the first time.

“We're trying to use Newpath (a BASF herbicide used in the Clearfield system) like propanil on these Clearfield varieties. These varieties won't tolerate Newpath at two applications. Since Newpath is both foliar and soil active, we can go out with a soil application (either preplant incorporated or pre-emerge), get some control from that, and then come back with a postemerge application.”

The test plots Baldwin has set up outside Lonoke, Ark., are a mish-mash of preplant incorporated followed by a post, pre-emerge followed by a post, and several sequential post-emergence applications (both early and later timed).

Newpath, an extremely slow-acting herbicide, is very good on most annual grasses, she says. The only thing it's weak on is sprangletop. It also misses some broadleaf weeds — hemp sesbania and northern joint vetch are particularly problematic. That's a reason Baldwin is looking at the effectiveness of some tank mixes.

“In this particular study, we haven't seen any post-emergence injury from Newpath. I have seen that — up to 40 percent injury with a post application — in earlier studies, though. Compared to plants that escaped damage, the Newpath injury didn't hurt yields significantly. It did, however, delay maturity from a few days to a week.”

The main symptom of injury from the herbicide is stunting of the plant. That's a hard thing to notice just looking across a field, says Baldwin. It's easier to spot in a plot.

“We use SuperWham to get rid of weeds Newpath won't get. Any of the propanil formulations make really good tank-mix partners for the second application of Newpath. I also like Aim, which is really good on hemp sesbania. Permit is also good, especially if yellow nutsedge is a problem.”

There are more-tolerant Clearfield varieties in the pipeline. The new Clearfield variety — CL 161 — is “much tougher” than the two Baldwin is currently working with. In research last year, Baldwin twice put a 5X rate of Newpath on CL 161 and didn't bother it. She “basically killed” CL 121 with the same treatment.

When CL161 becomes available, Baldwin thinks one of the favorite treatments will be Command pre followed by an early post-emergence application of Newpath. Then, just prior to permanent flood, farmers can apply another shot of Newpath with any needed tank mix partners. Growers can then “fertilize it, roll the water on and hopefully be done for the year.”

Like Command, Newpath must have water to be activated. That's especially true if farmers are going to use it as a soil application. If you put it out preplant incorporated and have good soil moisture to get seedlings up, you'll be in good shape.

“Using it pre-emergence instead of preplant incorporated and spreading it on the soil surface, I like to have a flush of irrigation water to make sure it's activated. Waiting for a rain that doesn't come or getting a drizzle that doesn't do the job isn't the way to go. You can flat miss a whole flush of red rice trying that.”

And having red rice survive in the Clearfield varieties brings up the bugaboo researchers face in growing this crop: outcrossing. When that occurs, the Newpath-tolerant gene gets into the red rice.

And Baldwin has seen it close up. In 2000, outcrossing occurred in several test plots she was working.

“We had simultaneous flowering between the Clearfield and red rice and so, when we harvested, we bagged seed. During the winter, we took those bags — from fields with 60 or 70 percent control — and found some mixes of a good ratio of red rice to Clearfield seed.”

Baldwin planted some flats in the greenhouse and started spraying them with Newpath when they reached two-leaf stage. She sprayed them again a week later with the standard rate of Newpath (4 ounces) and then waited to see what survived.

“We had some plants come through and we started thinking, ‘Uh-oh, this isn't good.’ At that time, we sprayed them with a double rate of Newpath. The plants that survived were transplanted to pots and allowed to grow to maturity. Some of the survivors turned out to be Clearfield rice and some were tolerant red rice.

“That led us to screen the whole area like we did the greenhouse tests. We sprayed 4 ounces at two-leaf and 4 ounces a week later, and a couple of weeks after that we hit it with a double rate of Newpath. We still had survivors.”

Everyone needs to be aware of the outcropping potential. If farmers have red rice plants still growing after Newpath applications, they need to go in and yank them out by hand, hand spray them — basically do everything possible to prevent those plants from going to seed, says Baldwin.

Environmentalists have been all over the outcropping potential. Horror stories about “super weeds” have been recited and Baldwin says at least some concern is justified.

“Rice is generally a self-pollinating crop. But pollen travels easily. The outcrossing percentage is low. Researchers looking into this say it's around 1 percent when they try and induce it. But it's happened in crops from sorghum to johnsongrass to some wild millet and sunflowers. Everyone must be very careful with this, make sure they switch crops when necessary and be smart with this new technology.”

e-mail: [email protected].

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