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Against barnyardgrass Diversify herbicides in rice fields

Last week I wrote about Command and how we will continue to depend on it as our first line of defense for barnyardgrass control in conventional and (in my opinion) Clearfield rice.

There are some situations where Prowl plus quinclorac (Facet or Quinstar) delayed pre-emergence can be substituted. Beyond that, however, the risk of uncontrolled barnyardgrass is greater if the Command is left off than the risk of resistance development is if it is used.

As a result, I see no viable alternative to using Command on most of the rice acres. The challenge then becomes how to continue to use Command on the bulk of the rice acres and prevent the spread of Command resistance.

At present, the only answer is to do a better job of barnyardgrass control in the rotated crop and to keep good diversity in the rice herbicide selection process.

One might ask, why not just rotate away from Command and strictly use postemergence herbicides as an alternative program? While it is possible to do this, there is a high risk of a grown-up mess.

Whether or not it is due to resistance, barnyardgrass has become much more difficult to control postemergence. If the grass ever emerges and is missed with the first shot at it, it seems we can not get it under control after that. As a result, my program has become: do everything you possibly can with soil residual herbicides before the barnyardgrass ever emerges — then go after what is left.

If any escaped barnyardgrass can be controlled following the Command application, there is little possibility of a resistance problem developing.

My concern is all of the fields where Command was used last season, some escapes occurred, and the farmer or consultant threw the kitchen sink at the escapes and did not kill them.

In conventional rice, I like the program a lot of consultants have gone to where they try to get two soil residual applications out before any grass emerges. In that program they will typically use Command pre-emergence and hopefully get a rain to activate it.

Then, if there is a good forecast of a rain or a flush is needed for rice emergence, they will go right back with another residual application. That application may be quinclorac alone or in a mixture with Prowl or in some cases more Command depending on the rate of Command used initially.

If there is any grass emerged at the time of this application, then a postemergence plus residual mixture should be used. Examples would be propanil, Ricestar HT or Clincher plus Command or quinclorac.

Another postemergence herbicide that is making a comeback is thiobencarb or Bolero. RiceCo sells a propanil plus thiobencarb mixture as Ricebeau that gets another mode of action in the program. A gallon of Ricebeau provides the “old” 3 plus 3 lb/A of propanil and Bolero we recommended years ago for barnyardgrass and sprangletop control.

Following Command or Prowl plus quinclorac, one of the above treatments can give you a quick one-two punch before the barnyardgrass ever gets started. The choice will depend upon the weeds, stage of growth and the treatment used previously. The key is to target the situation and also get some herbicide diversity into the program.

If Command is used early, then a propanil, Ricestar HT or Clincher plus quinclorac will provide two additional modes of action. Ricebeau plus quinclorac will provide three. You can also add some additional Command to some of these.

You may say, “That is a chunk to spend before I see much grass!” It is, but if you spend it then and kill the grass, that is better than spending a chunk later and it still growing up.

We will go from here next week.

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