SIDEBAR: How Weeds Build Herbicide Resistance
Herbicide resistance a major problem in agriculture
By John Lovett – May 23, 2024
FAYETTEVILLE, Ark. — Herbicide-resistant weeds are the most problematic and expensive management issue in row-crop agriculture, according to Nilda Burgos, professor of weed physiology and molecular biology with the Arkansas Agricultural Experiment Station.
A field infested with water and nutrient-stealing Palmer pigweed and barnyardgrass can become unproductive because those weeds can’t be controlled by herbicides, Burgos said. She is studying the broad-spectrum capabilities of a non-chemical solution — microwaves — to decrease the weed seeds in the ground and potentially curb herbicide-resistant weed evolution.
Synthetic chemical herbicides are popular, Burgos said, because they are usually effective on a broad spectrum of weeds and are more effective than natural herbicides. However, the chemicals generally target just one enzyme to disrupt a weed’s ability to function. Palmer pigweed, for example, builds resistance to the herbicide glyphosate by producing dozens of copies of the gene that produces the enzyme targeted by glyphosate.
“The recommended dose of glyphosate is not sufficient to inhibit all the extra copies of the target, so the pigweed harboring this capability survives,” Burgos said. “In most cases, weed populations become resistant to herbicides due to selection of plants with a mutation in the herbicide target that prevents interaction with the herbicide.”
Herbicide-resistant mutants are extremely rare, Burgos adds, but the possibility of selecting them increases with the number of plants being exposed and the frequency of herbicide use.
The risk of selecting such mutants also increases with genetic diversity of the weed, Burgos noted. Some plants in a farmer’s field could receive a sublethal dose of the herbicide due to various reasons — variable weed density, shading by adjacent plants, or weeds larger than optimum size. In that case, Burgos said the plants would survive by natural protection from herbicide damage or minimal ability to detoxify the herbicide.
“Repeated exposure to sublethal doses favors plants with higher tolerance, eventually resulting in a resistant field population,” Burgos said. “Palmer pigweed has all the ideal traits for resistance evolution. It has high genetic diversity and can grow 2 to 3 inches daily, produce up to 1 million seeds per plant and emerge throughout the growing season. Thus, Palmer pigweed has become resistant to many herbicides, including glyphosate.”
The study exploring microwave technology as a non-chemical solution is part of a larger weed science investigation supported by a nearly $300,000 Agriculture and Food Research Initiative grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture, with additional support from The Cotton Board and Cotton Incorporated.
To learn more about the Division of Agriculture research, visit the Arkansas Agricultural Experiment Station website. Follow us on 𝕏 at @ArkAgResearch, subscribe to the Food, Farms and Forests podcast and sign up for our monthly newsletter, the Arkansas Agricultural Research Report. To learn more about the Division of Agriculture, visit uada.edu. Follow us on 𝕏 at @AgInArk. To learn about extension programs in Arkansas, contact your local Cooperative Extension Service agent or visit uaex.uada.edu.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen agriculture, communities, and families by connecting trusted research to the adoption of best practices. Through the Agricultural Experiment Station and the Cooperative Extension Service, the Division of Agriculture conducts research and extension work within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension and Research programs and services without regard to race, color, sex, gender identity, sexual orientation, national origin, religion, age, disability, marital or veteran status, genetic information, or any other legally protected status, and is an Affirmative Action/Equal Opportunity Employer.
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