RESEARCHERS from the journal Weed Science have found rotation is critical in managing the impact of herbicide resistant weeds.
Numbers of giant ragweed, a major pest in the American Midwest, where it has serious impact on corn and soybean yields, are shown to decline by up to 38pc when break crops such as wheat or lucerne, known as alfafa in North America, are incorporated in the rotation.
Giant ragweed is resistant to multiple herbicide modes of action.
Researchers from the University of Minnesota looked into whether non-chemical control methods could lower plant numbers.
They evaluated six, three-year crop rotation systems, including continuous corn, soybean-corn-corn, corn-soybean-corn, soybean-wheat-corn, soybean-alfalfa-corn and alfalfa-alfalfa-corn.
The wheat and alfafa-based systems were clear winners, with 38pc fewer giant ragweed plants.
It also found that due to the short-lived nature of giant ragweed seed, a zero-weed threshold also works well in depleting the seedbank quickly.
When a zero-weed threshold was maintained, 96 percent of the giant ragweed seedbank was depleted within just two years.
However, in terms of problem herbicide resistant weeds in Australia this is not as effective as they have a long dormancy period.
The rotational work, however, may help Australian weed management experts with further clues about how to manage major problem weeds such as ryegrass and wild radish.