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Mid-South farmers need new herbicides

Around 10 years ago weed scientists in general had gone from believing that resistance to herbicides was not likely to understanding that it could happen. We learned that with some families of herbicides it was very likely to happen and it would happen in multiple species.

There was still an overriding feeling that weed resistance would never be a real serious problem.

Part of that perception might have been due to the relatively fast-paced introduction of new herbicides from various classes of chemistry or herbicides with different modes of action (that is, the way they kill a plant).

It seemed that with most weeds, there were at least one or two choices for herbicides. In addition, Roundup Ready, Liberty Link and Clearfield crops were being developed and the future seemed bright.

I have been with the University of Arkansas for five years now. I am concerned that in those five years I have now worked on three confirmed glyphosate-resistant weeds: Palmer amaranth, common ragweed and horseweed. We are currently in the process of screening a fourth weed, giant ragweed, which at least has a range of susceptibility from population to population.

It seems like at least once every two to three months someone asks me to look at another weed for tolerance to glyphosate.

As far as other herbicides go, one of my research counterparts in Fayetteville, Ark., Nilda Burgos, has confirmed the presence of ALS-resistant ryegrass. She and I also confirmed one of the first cases of red rice resistance to Newpath herbicide (although this was from out-crossing).

Here at the Lonoke, Ark., center, we are investigating a horseweed that we believe is ALS resistant. It all leaves me to wonder what will be next.

Why is resistance so much of a concern now? The problem is our heavy reliance on one or two herbicides or herbicide modes of action for weed control. Another problem is that herbicides are more efficient and economical than tillage. In addition, the benefits of reduced tillage in terms of time management, soil conservation and moisture savings have pushed growers in this direction.

There is little coming that I can see that will change this.

I recently attended an excellent meeting on glyphosate resistance that was organized by Stephen Duke and Steve Powles in Chicago. It was held in conjunction with the American Chemical Association annual meeting. During a forum at the end, we discussed strategies for resistance management. It did not give me a warm fuzzy feeling.

We have an over-riding problem in terms of dealing with herbicide resistance — no new chemistry. Most strategies put forth by the group involved the reliance on old standby products and the continued use of the products with resistance currently developing.

For example, in Arkansas we are almost completely reliant on one compound, dicamba, for control of glyphosate-resistant horseweed.

Some of the companies believe that financial incentives for resistance management will have an impact. I do not believe the numbers we discussed will be enough. In the end, the farmer will be asked to pay for managing resistant weeds, while still paying a full premium on seed and full price on herbicides.

The solution lies in providing growers with alternative chemistries that provide at least similar ease and simplicity to glyphosate. The bar has been raised, and due to the way we farm now, the bar cannot come down.

One reason that there are few new technologies coming has been a shift of money away from ag chemical development to seed traits. Meanwhile the cost of developing, registering and producing a new herbicide has steadily increased.

For any real changes some of those dollars must go back to the chemical side one way or another. There is an opportunity for ag chemical companies to seize the opportunity that is now evolving and develop new products to solve tomorrow's problems.

I do not mean to be preaching too much doom and gloom. Both the companies and the university have some good herbicide resistance suggestions and programs available for consideration. I just do not like the overall situation in terms of weed resistance and alternative control options that I see coming.

There are a few relatively new products like Valor and new uses of old products, like the use of Reflex herbicide applied pre in soybeans (as the pre-mix Prefix (Dual + Reflex)) and there are a small number of new experimental products that companies are almost ready to talk about.

In addition, there are new herbicide-tolerant crops coming, like STS/RR stacked soybeans (GAT), Ignite-tolerant crops, and dicamba/RR stacked crops. STS and dicamba stacked crops will undoubtedly help in some areas, but we already have ALS-resistant weeds (STS) and a heavy reliance on dicamba.

Hopefully some companies can find a way to invest in new technology and we can get some new herbicides to help out this new/old technology.

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