Herbicide resistance problem is real

Low peanut and cotton prices, high cost of production, soaring fuel prices, and scarce labor are all reasons for Southeastern row crop farmers to worry. Yet, all are dwarfed by the possible ramifications of herbicide resistance.

At the last Beltwide Cotton Conference, Alan York, who is one of, if not the top, cotton weed scientists in the country, told growers about the growing risk of over-use of glyphosate and subsequent resistance of Palmer amaranth pigweed. His comments were reported in January 2006 in the Farm Press and other magazines. Throughout the Southeast, winter 2006 crop meetings were highlighted by resistance management programs.

Despite the dire predictions, little was done to reduce or eliminate pigweed resistance to glyphosate, and in 2006, the problem has grown exponentially. York said in a recent phone conference with media representatives that pigweed resistance to herbicides has the potential to be a bigger problem for cotton farmers than the boll weevil.

York, who is a professor and researcher at North Carolina State University, has worked with cotton farmers and herbicides in the state for nearly 30 years. From the old school and not prone to making dramatic statements, York's assessment of the potential problem is one that should carry substantial weight for cotton growers.

In the Southeast, cotton has become the preferred crop rotation for hundreds of thousands of peanut acres. Roundup Ready technology, ease and effectiveness of glyphosate-based herbicide programs and advances in no-till farming have made cotton and peanuts an economic necessity for many farmers.

For peanut farmers ALS-inhibiting herbicides are every bit as important as glyphosate is to cotton farmers using Roundup Ready technology. In 2005, Palmer amaranth pigweed that was suspected of having built up resistance to ALS herbicides was documented. Now, researchers are close to documenting a case of crossover resistance by pigweed to ALS herbicides and glyphosate. An obvious, but terribly flawed remedy to glyphosate resistance in cotton is the use of ALS-inhibiting herbicides, because they work so well in peanuts and other crops. The problem is not so much glyphosate or ALS-inhibiting chemistry, rather the prolific biology of pigweed. Swapping glyphosate use in cotton for ALS herbicides, then using the same family of herbicides the following year in peanuts will guarantee a more rapid resistance problem.

It seems like there is an easy solution — don't use glyphosate or ALS herbicides. The reality is that too many farmers either don't understand the risk or can't afford the alternative herbicide schedule.

In cotton, replacing glyphosate-based herbicides that cost in the $12-15 per acre range with a Cadillac treatment of pre-emergence, early post-emergence, directed over-the-top and lay-by applications cost more than $40 per acre — just for the herbicides. Variations of the Cadillac treatment may be in the $25-30 range, but nowhere close to the cost of using glyphosate as a broad spectrum weed control system.

In peanuts, the cost of replacing ALS herbicides is not so dire, perhaps as little as $10 per acre more, depending on weed complex. The question is efficacy of these alternative herbicides, which require more precise timing and application skills than glyphosate. And, peanut producers face more severely restricted prices for their crop, making the dollar to dollar comparison with cotton fairly close.

Coping with the problem of herbicide resistance won't be easy to manage or cost-efficient, but it will likely determine whether some growers stay in business. For the 2007 crop, it will be critical for growers to understand the mode of action of all the herbicides they use and to plan their cropping system based on how these materials can be used effectively on various crops.

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