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Resistant weed? Better safe than sorry

This season is getting away in a hurry — especially for rice. The weed control season is over for all practical purposes.

I have received an increasing number of calls from consultants who have not been able to control barnyardgrass in certain fields. The complaints have not been on any particular herbicide.

The disturbing part is that in a lot of the fields they have used most all of the available herbicides or herbicide modes of action. They have “thrown the kitchen sink” at the barnyardgrass and often have not slowed it down.

One thing I observe — at least, think I observe — is barnyardgrass gets much harder to control when conditions are hot and dry in June and early July. This usually affects only late-planted rice.

I often get comments along the lines that “this herbicide or that herbicide worked great all season, but in the past couple of weeks I have not been able to control anything with it.”

Sometimes herbicides just do not work and escapes occur. However, in situations where you feel conditions were right and you did everything right, it needs to be determined why the failure occurred if possible.

Of course, my concern is always herbicide resistance. Not all failures are due to resistance. In fact far more failures occur for other reasons. However, we continue to push certain modes of action in our rice herbicides very hard and we are not getting any new ones.

The University of Arkansas has an excellent herbicide resistance testing program headed up by Jason Norsworthy. You can get in touch with Jason, or other University of Arkansas weed scientists, through Arkansas county Extension agents and they can assist you with sampling instructions.

There have been several fields this year where I suggested barnyardgrass plants be dug with the mud attached and placed in buckets of water and taken to Bob Scott at Lonoke, Ark. Those plants can be grown out and seed can be collected. This usually assures seed will be obtained.

Others choose to wait and harvest mature seed heads. The problem with that is by the time the crop gets that far, everyone is so ready to get out of the field that good intentions often go by the wayside and the seed do not get harvested.

I am certainly not suggesting the university guys get covered up with seed from every field where a failure occurred. However, in those fields like I am getting calls on where it would sound like things should have worked, I strongly suggest you sample them.

If you sample a field and resistance to certain herbicide modes of action are confirmed, alternative plans can be made. If it is determined that a suspected sample is not resistant, then we can look for other reasons why the failure occurred and perhaps correct it.


TAGS: Soybean
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