With resistant pigweed, control may have become more complicated but producers, “still have options,” Osborne said. “Yellow herbicides still work. A generation of farmers, however, may have grown up with Roundup technology,” and will now have to understand the new environment and go back to some older practices.

“If we use yellow herbicides properly, they are worth the price,” he said. He cited Treflan and Prowl as standbys and good options. Each product has specific requirements, however.

Treflan must be incorporated quickly. “It will not set out in the sun and wait for rain. It breaks down in sunlight. Tillage is the best means of incorporating.”

Prowl “will set out a few weeks,” Osborne said. Tillage incorporation is effective but rainfall or irrigation also do well and can move the material through residue. “Producers may need to increase the rate in heavy residue,” he said.

Both of those products are effective on Palmer amaranth in addition to other annual grass and small-seeded broadleaf weed species, he said, and should be considered in an overall weed control program.

Producers have a lot of pre-emerge herbicide options, used behind the planter and before the cotton and weeds emerge. But growers should do some homework before they select a product. “Know the soil type,” Osborne said. “The possibility of injury exists with some products in some soil types.” Also, rainfall or irrigation will be necessary to activate the products. “We have to have it and sometimes the Southwest struggles to get rain. Since most of our rain comes in April, May and June, we need to focus on the front end of the season to make residual herbicides work here in the Southwest. It’s easier if producers have sprinklers, but not everyone does.”

Over-the-top herbicide options include Roundup and Liberty (on appropriate tolerant varieties), Staple, Warrant, Dual and Prowl. Liberty, Osborne said, is not the preferred product for pigweed here in the Southwest. He also noted the importance of label instructions and timing.

“Each product has label restrictions,” he said. “Know the limitations and the make a plan. Some products have no burn-down effect, only residual.”

Post-emergence materials include Caparol, Cotoran, Karmex, Direx, Layby Pro and Aim. “These may provide burn-down and residual effects but may also injure cotton.” Spray applications that shield the cotton plant may be necessary.

In the new environment of herbicide-resistant weeds, the key to a successful weed control program, Osborne said, is use of residual herbicides. “Those products reduce early season competition and trips across the field while saving fuel and adding different modes of action. Residual herbicides can help to preserve current technology.”

Osborne said when new herbicide crop systems from Monsanto and Dow come out in the next two years or so OSU will look to see where they fit best. “They have shown excellent crop tolerance. And both systems offer remedies to most of our current weed problems. But product stewardship will be important. Scouting weeds and application timing will be important. We also will look at affordability. How much can we afford to pay?”

The systems, which will include either 2, 4-D or dicamba tolerance in a stacked trait variety along with glyphosate and glufosinate, will mean learning new weed control tactics. “Education will be the key,” Osborne said.

Cotton farmers may find more information on herbicide options on the Internet at http://cotton.okstate.edu/.

Information includes product listings, including mode of action.


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Consider resistance in weed management strategies