Bill McGoogan, who farms near Lumber Bridge, N.C., first noticed some pigweed in one of his soybean fields that had been sprayed with glyphosate. He went back and sprayed it again with glyphosate, making sure to get good coverage.

“The second time I sprayed it, I knew I had good coverage and nothing happened with the pigweed. I called Monsanto, and they came and sprayed a 3X and a 6X rate of Weathermax, and it still had little effect” the North Carolina farmer says.

In 2005, McGoogan says he didn’t see any other real bad spots, though there were Palmer pigweed escapes throughout his farm. Pigweed escapes are not at all uncommon, and he couldn’t pinpoint for certain that any of these were caused by herbicide resistance.

After finding the resistant pigweed in his soybeans, McGoogan began noticing patches of weeds in neighboring fields.

In 2006, the resistant pigweed spread to cotton and soybean fields. On cotton, he used 24 ounces per acre of Weathermax, plus 1.7 pints of Staple. When that didn’t control the pigweed, he put on a second application of 24 ounces of Weathermax, and did not control the weeds.

Already looking toward the 2007 season, McGoogan tried three different combinations of pre-plant, residual herbicides in test plots on his farm. His goal is to help keep pigweed under control for 4 or 5 weeks after cotton is planted. In these test plots, he used Prowl alone, Reflex alone, and Prowl plus a pint of Direx.

The best combination, he says, was Prowl H20, and he got similar results with Prowl plus a pint of Direx, Prowl alone cost $4-5 per acre and a pint of Direx adds another $2 to the tab. Reflex did not perform as well in McGoogan’s test and cost about $11 per acre.

In the 2006 test, the North Carolina farmer said conditions were nearly perfect for using a pre-plant material. Adequate rainfall after he applied the test plots of Prowl, Prowl plus Direx and Reflex gave each material the opportunity to work.

A big knock on pendamethalin, which Prowl is one of a number of herbicides available, is failure to work properly without adequate moisture

In 2007, McGoogan says he will probably go back to more cultivation, use pre-plant residual herbicides, most likely Prowl, then come back at the four leaf stage and apply Weathermax. Within a week or so after applying Weathermax, he will likely come back and cultivate and use a post-directed spray, probably Cotoran and MSMA.

For farmers who document cases of resistance on the farms, he says, plan on the problem getting much bigger the following year. “I thought, maybe it won’t carry through from one year to the next, but it does. If you see an isolated area this year, you better count on it being a quarter or half the field the next year,” he says.

e-mail: rroberson@farmpress.com