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Rotate crops, herbicides for resistance management

There was an article in our local newspaper recently stating that so far all of our new crop rice had tested clean for LibertyLink. That is great news and it fits right into what I want to write about — in two ways.

Last week I stated that rice prices need to strengthen to put rice back on a level playing field with other grains. Hopefully this will help. Because of the high input costs for rice compared to most alternative crops, rice prices really need to be more favorable than the other grains.

I also started a topic last week about herbicide resistance and the fact that the most recently discovered example was barnyardgrass resistance to Command.

I wrote in that article that between the barnyardgrass species we have in Arkansas and related species occurring in other states and countries, resistance has been documented for most of our major herbicide modes of action. Examples include resistance to quinclorac (Facet and others), propanil and now Command in Arkansas; and resistance to the ACC’ase inhibiting herbicides such as Clincher and Ricestar HT and ALS inhibiting herbicides such as Regiment, Grasp, Beyond and Newpath in California and other countries.

Before I get a nasty call, this does not mean examples have been found for each individual herbicide mentioned. However, once a weed demonstrates resistance to a mode of action, it places all of the herbicides with that mode of action on the radar screen.

The first step in barnyardgrass resistance management is going to require doing everything we can with technology we now have. The broad categories there are crop rotation and herbicide rotation.

The other step is eventually going to have to be the development of some new technology. The technology we have today can carry us only so far.

Farmers will determine what the crop rotations will be. I can give a lot of advice on herbicide usage, but I can never tell a farmer what crop he should plant in a field.

I can say in general terms that the more you rotate, the better off you will be from a resistance management standpoint. Some learned that corn following rice can sometimes be a tough rotation. I heard one scientist say that “corn following rice is a no-no and corn following Clearfield rice is a h___ no-no.

A lot of ground in Arkansas is better-suited to rice than other crops. A lot of it is zero graded and was shaped with the intent of water seeding. There are fields where water seeded rice has been grown continuously for years.

While some weeds are difficult to control in water seeded rice, barnyardgrass control can be relatively easy. Through the years much of the good intent on water seeding has gone by the wayside and a lot of these flat fields are being dry seeded.

Growing continuous rice in these fields, attempting to use the Clearfield technology as the vehicle, is a red flag to me from both a red rice and barnyardgrass resistance standpoint.

The second step in resistance management with current technology is a good herbicide rotation program. Certain herbicides are basic and Command is one of them. It will likely continue to be used in most fields. However it must be backed up with a mixture of different herbicide modes of action.

Tank mixtures are one means of resistance management and rotating modes of action is another. Several of the postemergence herbicides for barnyardgrass control will do similar things, but have different modes of action. We can do a lot with existing technology if it is managed properly. However, technology must also move forward. I will start here next week.


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