Crop Tech Corner

Study Shows Herbicide Rotation Alone Can't Stop Weed Resistance

Emily Unglesbee
By  Emily Unglesbee , DTN Staff Reporter
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Rotating herbicides to avoid weed resistance is not a magic bullet against resistance development, according to a new study from the University of Illinois. (DTN photo illustration by Nick Scalise)

ROCKVILLE, Md. (DTN) -- This bi-monthly column condenses the latest news in the field of crop technology, research and products.


Rotating herbicides to avoid weed resistance is not a magic bullet against resistance development, according to a new study from the University of Illinois. In the past, researchers have assumed that many of the random genetic mutations that help weeds survive a herbicide application come with a "fitness cost," meaning the mutated weeds are not as strong and productive as the susceptible weeds. From a painstaking study done with waterhemp plants, Illinois crop scientist Pat Tranel and his team discovered this was not the case. Over six generations, the waterhemp plants in their test population with herbicide resistance survived and reproduced at the same rate as susceptible waterhemp plants.

This is tough news for any farmers who believe all they need to do to avoid weed resistance is spray an alternate herbicide mode of action every other year. Because no herbicide kills 100% of a weed population, there is a good chance that resistant genes to a certain herbicide will still be in the field even after a year or multiple years of using a different chemical, the Illinois researchers concluded.

"This study tells us that fitness cost isn't going to help you much in terms of herbicide resistance, so even long rotations aren't going to work," Tranel said in a university press release. "I tell farmers, 'Once you have resistance, you're stuck with it.' It gives us that much more incentive to do the right things to avoid resistance in the first place." That means using multiple herbicide modes of action during single applications, following pre-emergence applications with post-emergence ones and even hand weeding any escapes if necessary, the researchers said.

See the press release here:… and the study abstract here:….


A public-private research partnership has yielded big dividends for soybean growers. Scientists from Dow AgroSciences and Purdue University teamed up to search for genetic resistance to soybean stem and root rot, which is caused by a fungus called Phytophthora sojae. The rotting diseases caused by Phytophthora fungi are some of the most economically damaging soybean diseases in the U.S. each year. The Dow and Purdue scientists pinpointed a gene called Rps11 that protects plants against a variety of types of this fungus. In a university press release, Dow asserts that it can use molecular markers to breed the gene into high-yielding elite soybean germplasm and make them widely available to farmers "rapidly." Purdue agronomist Jianxin Ma added that they will continue to search for additional resistance genes that could someday be stacked with Rps11 for even better resistance and longevity.

You can read more about the discovery in the Purdue press release here:….


Move over corn and soybeans -- there's a new biofuel source in town. Scientists from the University of Illinois have produced a promising economic analysis of genetically engineered (GE) sugarcane that produces an oil called lipidcane, which can be converted into biodiesel or jet fuel. The sugarcane is the result of an Illinois project called Plants Engineered to Replace Oil in Sugarcane and Sweet Sorghum (PETROSS), initiated and funded by a Department of Energy branch called the Advanced Research Projects Agency - Energy (ARPA-E).

The more lipidcane a sugarcane plant produces, the better. The theoretical limit (and researchers' goal) is 20%. In their study, the Illinois researchers concluded that these new sugarcane plants promise to be remarkably efficient at producing biofuel. They estimate that a sugarcane plant with 20% lipidcane can produce "more than 15 times more jet fuel (6,307 liters, or 1,666 gallons) per hectare than soybeans," according to a university press release. Even a sugarcane plant with only 5% lipidcane content could still produce four times more jet fuel than soybeans.

PETROSS researchers are also working to make the GE sugarcane more cold-tolerant, with the goal of growing it on marginal lands in the Southeast U.S. not suited to other row crops. The director of PETROSS, University of Illinois crop scientist Stephen Long, estimates that if this new sugarcane were grown on 23 million available marginal acres in the Southeast, the resulting fuel could account for 65% of the nation's jet fuel consumption.

Read more about the researchers' work from the university press release here:… and the study here:…. Read more about the PETROSS effort to make oil-producing sugarcane here:….

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Emily Unglesbee