New Milestone in Herbicide Resistance Fight
Herbicide-resistant weeds are an ever-growing menace for crop producers in every part of the U.S. as well as other major agricultural regions around the world. Three of the most noxious agricultural weeds are waterhemp, smooth pigweed, and Palmer amaranth which lead to untold production losses on top of additional production costs every year.
In the “2020 Herbicide Guide for Iowa Corn and Soybean Production ,” released earlier this year, Iowa State weed scientists Bob Hartzler and Prashant Jha warn that the rapid increase in herbicide resistance across the corn belt is a serious threat to the current production system, with increasing numbers of herbicide-resistant biotypes being identified every year. They contend that weeds are evolving to resist herbicides in a new way and poses unique threats compared to other resistance mechanisms. Basically, the way these plants are able to resist one chemical may make them able to more easily resist others.
What they are talking about is called non-target-site or metabolic-based resistance (MBR), which allows weeds to literally detoxify herbicides before they can cause damage. As Hartzler and Jha explain, researchers don’t know whether these metabolic changes provide resistance to one herbicide group will affect other, unrelated herbicides. “Each situation will need to be evaluated individually to determine the extent of cross or multiple resistance.” But it’s pretty evident that this superpower poses an enormous threat.
One of the latest milestones in the fight against these “superweeds” is a landmark study that includes some of the most comprehensive genome information to date for waterhemp, smooth pigweed, and Palmer amaranth that they hope can help speed the discovery of new solutions. Pat Tranel, professor and associate head of the Department of Crop Sciences at the University of Illinois and co-author on the “Genome Biology and Evolution” study says the techniques they used provide a much clearer and richer picture of the species’ gene sequences, a requisite for many genomic studies.
It’s hoped that these details will allow researchers to narrow down where resistance is happening. For instance, it is usually very difficult to determine which specific enzyme, among hundreds, is responsible for detoxifying the herbicide. Now, researchers will essentially be able to sort through a list to find the culprit with the hope of either knocking out the enzyme responsible or modifying the herbicide molecule to evade detoxification.
Obviously, there is a lot of work still ahead which means producers will have to continue making the most of the tools available. In their 2020 Herbicide Guide, Hartzler and Jha conclude that “herbicides alone cannot win this battle. Production systems must be evaluated to determine what alternative strategies can be used to supplement herbicides.” They believe it is critical to develop herbicide programs that rely on multiple effective herbicide groups and provide full-season weed control, therefore minimizing weed seed production. While they admit that control methods such as narrower row spacing, planting cover crops, or harvest weed seed control methods do not provide the ‘big impact’ of herbicides, an effective mix is the only way to preserve the effectiveness of existing and new herbicide tools into the future, according to Hartzler and Jha.
If you are looking for more information to help your own operation manage herbicide, fungicide, and insect resistance, you might check out Take Action. They describe themselves as a farmer-focused education platform that helps farmers adopt management practices that lessen the impacts of resistant pests and preserve current and future crop protection technology. Their website has a ton of information including some really handy classification charts for herbicide, fungicide, and insecticide that can help producers identify the most effective chemicals for their needs. Click HERE . (Sources: High Plains Journal, PhysOrg, University of Illinois, University of Iowa, ERS)
