Keeping herbicide-resistant pigweeds from producing seed will work to reduce resistant weeds in fields, as shown by research being conducted by the University of Arkansas Extension Service, under the direction of project leader and Extension weed scientists Ken Smith.

Pigweeds produce between 500,000 to 2 million seeds per plant, but those seeds aren’t that hardy compared to some other weed seed. The seed has a relatively short four-year viability in the soil; therefore, keeping pigweeds from maturing to seed bearing is being called Zero Tolerance by Smith.

Previous programs under research has been to eliminate herbicide-resistant pigweeds with deep burial by major tillage and a cover crop planted to help prevent germination until seed is no longer viable.

As reported in an Extension news release quoting Smith, the Zero Tolerance program seems to have more success potential, but the problem is that hand hoeing manual labor is required for Zero Tolerance. Old-fashioned hand-hoeing, along with pre-plant, post-emerge and layby herbicide applications are involved; therefore, it is not easy or inexpensive to try and achieve Zero Tolerance. Selecting the right herbicides to limit the hand hoeing is key, too.

“The Zero Tolerance concept prevents the seed bank from being replenished by stopping the seed before they form and allowing depletion over time,” Smith said.

Last year and this year a 68-acre plot in Marvell, Ark., is being used for the research. Smith reported, “The number of pigweed this spring is approximately 10 percent of the population last spring when Zero Tolerance was initiated.”

No pigweeds went to seed in the field in 2010, and keeping that purity again in 2011 is the goal. The manual labor for the field involved four people hand-hoeing the field four times in 2010. The 68-acre field required about two hours of hand-hoeing per acre.

“It’s amazing how the population of pigweed has been reduced,” Smith said. “And it’s exactly what we predicted: that we would have 90 percent reduction of the seed bank in the first year.”

Putting the Zero Tolerance program into effect for a commercial-sized farm is limited because of the labor-intensiveness. “The 90 percent reduction is not something we can achieve farmwide in year one, but maybe we can creep it up and creep it up over consecutive seasons,” Smith said.

Research is continuing including the combination of herbicides to use in conjunction with the hand-hoeing. Fewer weeds escaping the herbicide means less time involved in hand labor. A field day in July will showcase results.