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Controlling grasses in rice

Last week I discussed the importance of controlling barnyardgrass in soybeans as the foundation for a resistance management program in rice. A barnyardgrass control program in soybeans incorporates both primary principles of a resistance management program — crop rotation and herbicide mode of action rotation.

This week I will tackle resistance management in the rice crop itself. That is a difficult task because barnyardgrass resistance has been documented for every major herbicide mode of action we have registered in rice. This makes a resistance management program based upon rotating herbicide modes of action somewhat of a challenge.

Hopefully this also helps explain why I feel like we cannot let the resistance situation get any worse.

To date only two fields have been confirmed in Arkansas to have barnyardgrass resistance to Command. Keep in mind, however, this does not mean the problem is isolated to those two fields. There could be (and probably are) problems out there in fields that have never had samples pulled for testing.

Command, in my opinion, is the foundation herbicide for grass control and one we can least afford to lose. When it is taken out of the weed control program, barnyardgrass control becomes much more difficult.

Even in Clearfield rice, some of the biggest grass control messes I see are where Command was left out of the program because the grower felt like the Newpath would provide adequate control.

This illustrates the Catch 22 we have without new technology. Clearfield rice would be the most logical place to be able to rotate away from Command as a resistance management tool. However, if you leave the Command off, then you wind up with tremendous selection pressure on the ALS inhibitor herbicides such as Newpath.

Widespread resistance to the ALS inhibitors will drastically reduce the usefulness of the Clearfield technology. Therefore, it is a darned if you do or darned if you don’t scenario.

One alternative to Command in both Clearfield and conventional rice is a treatment of Prowl plus Facet or Quinstar (quinclorac) delayed pre-emergence. Even though the price of quinclorac has come down, this tank mix is still more expensive than Command.

In addition, the delayed pre-emergence treatments are not as straight forward to use as just spraying immediately after planting. Resistance to quinclorac is fairly common in Arkansas but research has shown there is less resistance to quinclorac soil-applied than to postemergence.

Prowl plus quinclorac delayed pre-emergence is an excellent treatment when properly used. Realistically though, I doubt if it takes a lot of acres away from Command.

I hear some talk about just using Prowl alone as a delayed pre-emergence treatment as a substitute for Command. Prowl is simply not effective enough to be a standalone treatment.

I also hear a lot of talk about just throwing some Prowl in with whatever is being applied since it is inexpensive. It is inexpensive and sometimes you might get something out of it. However, it should not be something you are depending on.

I wish we had an alternative mode of action that was as economical and effective as Command so we could effectively alternate pre-emergence herbicides, but we simply do not.

Unless you can effectively make the Prowl plus quinclorac delayed pre-emergence treatment work for you, the difficulty of controlling barnyardgrass postemergence if you leave off the Command is a bigger short-term problem than the risk of resistance if you continue to use it.

However, as we continue to use Command as our foundation herbicide, any escapes must be controlled. This is often easier said than done.

We will start here next week.


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