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Battle Continues On Resistant


Virulently resistant, Palmer amaranth (aka Palmer pigweed) in cotton is similar to Formosan termites or cockroaches. It’s a whole lot better to prevent the pest than face the costly and perhaps endless problem of trying to get rid of it.

In Georgia, where resistant pigweed hit early and hard a few years ago, there is optimism that 2009 will mark a turning point toward that proverbial light at the end of the tunnel in prevention and management.

Everywhere across the Cotton Belt there is worry that this may be the year of a “blowup” like Georgia and the Carolinas have seen, especially if too many farmers try to cut costs by skipping residual herbicides or cutting rates.

“In 2007 and 2008 we made great progress helping Georgia growers realize how serious a threat resistant Palmer is to their ability to continue producing cotton and using conservation tillage,” says Dr. Stanley Culpepper, University of Georgia Extension weed scientist.

“The attendance and comments of producers at winter meetings, and the surveys of our county agents, have convinced me that growers are very serious about this pest. They now understand its movement, seed production capability, and how in just about three years it can come to dominate a landscape.”

The alarm has gone off – in North Carolina, which along with Georgia was first to see how Palmer amaranth can turn a cotton field into an intractable weed farm almost overnight – and in Tennessee, Mississippi, Alabama, and Arkansas. Points west like Texas and Louisiana have taken notice and are on alert, expecting to see more encroachment of resistant Palmer this year.

Economic Uncertainties

The economic uncertainties of the 2009 growing season will be a real test on many farms. Seeing a reduction of commodity prices after record costs for fuel, fertilizer, biotechnology fees and even land rents, some producers now are hit with higher costs of credit.

Dr. Larry Steckel, University of Tennessee weed scientist, has called Palmer amaranth the biggest threat to cotton since the boll weevil. He also is concerned about today’s economy bringing about a bad trade-off among some producers.

“With last year’s prices growers were more willing to use residuals, but this year they may not see a real need and try to get by,” he says. “In fact, I have no doubt. I just hope enough folks heed the warnings, get some pre-emerge applications out there, take advantage of any rebates or bargains the companies offer.”

Residual Programs

Resistance strategies in Georgia and other universities usually offer several alternatives for combinations that can be used if the resistance is to glyphosate or ALS inhibitors (or both), irrigated or dryland, full resistance or moderate to heavy sensitivity, and what herbicide tolerances are included in the variety.

The resistant weed spectrum on the farm is a major consideration, and with all these variables some producers will need agronomic advice on the best herbicide combinations.

“A full post-patent program can be developed now that MANA has added Cotoran 4L and Pyrimax 3.2L (Pyrithiobac-sodium, or Staple) to its cotton line,” says Dr. Duane Martin, MANA manager of new business and product development.

A program of this type could include:

• Triflurex HFP pre-plant incorporated followed by Cotoran 4L pre-emergence.

• Diuron 4L or Pyrimax 3.2L plus Cotoran 4L for pre-emergence.

• Glyphogan plus Pyrimax 3.2L or Parallel PCS (metolachlor) post-emergence over the top.

• Cotton Pro (prometryn) plus MSMA or Cotoran 4L plus MSMA for post-emergence directed.

Regardless of what residual herbicide program is used, it’s going to be more cost-effective than waiting until Palmer amaranth has infested a cotton field,” says Culpepper.

MANA contributed information for this article.

Develop A Plan For Battling Pigweed

• Make good use of residual herbicides.

• Monitor fields closely.

• Don’t wait too late.

• Implement aggressive scouting.

• Use effective tankmixes.

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