Heed crop rotation issues with Clearfield rice system

Clearfield rice was grown on approximately 560,000 acres last season and there will be upwards of 850,000 acres worth of seed in 2005.

The varieties and hybrids available for 2005 will include CL 161, CL 131, Clearfield XL8 and Clearfield XP730. Most of the CL 131 will be for seed production. It is my understanding that the amount of Clearfield XP730 will be limited. (As a side note, it is my opinion that the CL131 being grown for seed should not be grown in red rice-infested fields.)

There have now been two commercial years for Clearfield rice, 2003 and 2004. There was seed production and some limited trial acres the year before that. I hope you have all kept track of where those fields were if you have grown Clearfield.

One major drawback of the Clearfield system, and more specifically Newpath herbicide, is that you must follow Clearfield rice with soybeans, another legume crop, corn (nine months) or fallow in order to get back into a regular rice rotation. That is, Clearfield rice and Newpath herbicide have an 18-month rotation to rice.

You can follow Clearfield rice with another year of Clearfield rice, but then you have the same problem again the following year if you want to somehow get back into a regular or conventional rice rotation.

Due to the potential for out-crossing, which has now been identified or is suspected in more than one field in Arkansas, the University of Arkansas and BASF Corporation recommend you rotate Clearfield rice with soybeans after one year to help prevent the buildup of resistant red rice.

That and striving for 100 percent control of red rice in a given season are the core of the stewardship program for Clearfield rice. The rotational problem is why at this time Clearfield rice has a very limited fit in continuous rice. You have no choice but to fallow the field or go back into Clearfield. This will allow red rice plants that escaped the Newpath last year to grow and prosper the following year.

I recently attended the Arkansas Soybean Research Conference in Brinkley, Ark. The attendance at this meeting was double what our soybean agronomist, Chris Tingle, had expected. I would like to say that the reason for the high attendance was to hear all the weed science information presented, but I am certain most folks came to hear about soybean rust. Most feel that there is a fair amount of uncertainty about just how bad the soybean rust problem will be.

I overheard a few growers say that the fungicide that they were going to use was called “Francis” until they figured out if the rust problem would be bad enough to affect the bottom line on soybean production. This was well and good, except one of the growers had grown Clearfield last year. So, he is limited to growing Clearfield again, which as mentioned above may cause problems from a resistance standpoint.

I'll bet that some of you are thinking about trying a field or two of regular rice following Clearfield rice. I just want to remind you that Newpath and Pursuit herbicides have the same active ingredient. The Pursuit rate for soybeans in a season is half the rate used in Clearfield rice with Newpath and the Pursuit label lists a 40-month rotation to rice.

The 18-month rotation interval is real; the Newpath label is more realistic than the Pursuit label, but it illustrates the concern. I do not recommend trying to get around it. The symptoms of Newpath carryover include stunted, yellow rice with necrotic leaf tips and possibly a “skippy” stand. Some rice may survive, but yields will be affected.

Some of you have asked about the possibility of labeling Beyond herbicide for two (or three) applications in Clearfield rice. Beyond does not have the residual that Newpath has and likely will not carryover to rice. We have looked at this some in the plots and it looks pretty good. However, Beyond is more expensive than Newpath and it is my understanding that the necessary residue studies, etc, have not been initiated.

So for now, Beyond probably will be limited to our 24C for salvage applications only after two Newpath applications have failed. Please check your records and plan your crop rotations well as we enter this third year of Clearfield rice production.

If you are picking up a new lease or buying a new rice farm, a good question to ask is, “Was Clearfield rice grown in this field last year?”

Bob Scott is the University of Arkansas Extension weed specialist. e-mail: [email protected]

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