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Arkansas rice: Research seeks answers for resistant weeds

The University of Arkansas has announced the confirmation of Command-resistant barnyardgrass. I have written in several articles that I see Palmer pigweed resistance in the row crops and barnyardgrass resistance in rice as the two biggest herbicide resistance threats (for the immediate future) in Arkansas.

Hopefully you can take both examples and relate them to the articles on the need for new technology that I and Bob Scott (University of Arkansas weed scientist) have been writing.

I do not believe that herbicide resistance in general should be a cause for panic.

However, it should be obvious to everyone that we need to make some changes in our weed control programs. The weeds are talking — is anybody listening? Perhaps better would be: the weeds are talking — are any farmers listening?

When I looked at Bob Scott's pigweed plots near Newport, Ark., there were several effective treatments in addition to glyphosate.

At that particular research location, the pigweed population is not yet glyphosate-resistant. There is no reason to believe, however, that herbicides other than glyphosate will behave any differently on a resistant versus a susceptible population.

One herbicide that has been effective for Palmer pigweed control — if properly activated — is Prefix applied pre-emergence. Prefix is a mixture of Dual and Reflex. This treatment has been highly touted around the South as a promising treatment for resistant pigweeds in both cotton and soybeans.

I think this treatment can help some and I do not wish to sound like “Uncle Scrooge.” In general, however, I do not believe pre-emergence herbicides are going to be much of an answer to any herbicide resistance problem in Southern row crops.

They weren't consistent in the 1970s and 1980s, and they won't be consistent now.

With Palmer pigweed in Arkansas, there is about a three-day window after planting to activate a pre-emergence herbicide. How often can one count on a rain in any given three-day period in the South?

In fact, in a lot of situations, a farmer does not even want a rain within the first three days after planting.

There was an excellent illustration of my point in Bob's plots. In one of the studies where Prefix and other pre-emergence herbicides were used, they irrigated with a sprinkler immediately after planting. There were some excellent treatments, including Prefix, in the test.

In a similar test he did not irrigate immediately and the same treatments failed.

Before the phone calls come, I am not being critical of anyone's herbicide or group of herbicides in general. We are going to have to try to make some of our existing herbicides work, or at least help, in a resistance management program.

Pre-emergence treatments will find a place in some situations.

However, except where overhead irrigation is available, folks need to remain realistic about the consistency of pre-emergence herbicides in the South.

Another herbicide that looked good in some of the research plots was Valor used in some of the burn-down treatments. Valor has some potential for soybean injury when used as a pre-emergence treatment.

I have seen the most injury when a rain occurs during or immediately after emergence.

The injury potential apparently can be reduced or eliminated by applying the treatment ahead of planting in a no-till situation.

Hopefully industry and university weed scientists will find the best way to fit this herbicide into a program because it does have good pigweed activity.

The treatments that “stole the show” in the pigweed plots were those that included Ignite in LibertyLink soybeans. I will start here next time.

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