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Reduced Herbicide Rates, Timely Cultivation As Effective As Full Rates

Reduced herbicide rates plus cultivation can be as effective as full herbicide rates, say researchers at the University of Wisconsin-Madison. A four-year study at the College of Agricultural and Life Sciences Arlington Agricultural Research Station showed that reduced rates integrated with cultivation decreased the annual weed seedbank in several tillage systems while maintaining crop yield.

“The results indicate that integrated weed management strategies can be successfully implemented without reducing crop grain yield and therefore, may increase net economic returns,” said CALS weed research scientist David Stoltenberg.

Stoltenberg and Dawit Mulugeta, a former graduate research assistant, compared continuous corn and corn-soybean rotation in no-tillage, chisel plow, and moldboard plow systems from 1992 through 1995. Common lambsquarters, giant foxtail, and redroot pigweed were the predominant weeds.

The researchers compared the influence of full-rate pre-emergence broadcasted herbicides, half-rate pre-emergence broadcasted herbicides plus inter-row cultivation, and full-rate pre-emergence banded herbicides plus cultivation (50 percent less herbicide applied per acre than the full-rate broadcast treatment).

At the end of the four years the researchers found that the weed seedbank decreased up to 50 percent for lambsquarters, 95 percent for giant foxtail, and 92 percent for redroot pigweed in both the full- and reduced-rate treatments across all tillage systems. According to Stoltenberg, crop rotation was not a major influence on changes in the weed seedbank, probably because of the simplicity of the rotation.

“Success of integrated weed management strategies, such as reduced rates, is largely dependent on careful and timely herbicide treatments and tillage operations,” said Stoltenberg. “Growers need to consider the increased time, labor, and management associated with mechanical methods such as cultivation.”

For example, if growers band-apply herbicides, they will need to rely heavily on inter-row cultivation to effectively manage weeds between the rows. Timely cultivation is important when weeds are still relatively young, and growers may need to cultivate more than once.

In contrast, if growers use a half-rate of broadcast herbicide, they may not need to cultivate. But, growers should be aware of what is going on in their fields by assessing weed emergence and be ready to go in and cultivate, Stoltenberg said.

If interested, growers should first try the reduced-rate approach on a few acres, where weeds have been effectively managed in the past. Integrated weed management strategies can provide both economic and environmental benefits to growers, and these strategies can also slow the development of herbicide-resistant weeds.

For more information, a June 1997 CALS press release on reduced herbicide rates is on the WorldWideWeb at