People who’ve read this column over the last few years might have guessed I’m a fan of pop culture references. And when it comes to resistant weed management, there’s no better pop culture reference than Jeff Goldblum’s Dr. Ian Malcom from “Jurassic Park.”
No, I haven’t seen the new “Jurassic World,” which has introduced Dr. Malcom to a whole new generation, but one of the quotes he’s most well-known for rings true time and again in resistance management: Life finds a way.
Never has this been truer than with today’s problem weeds — like Palmer amaranth, which is resistant to multiple modes and sites of action in parts of the U.S. Some growers have discussed or tried alternatives to chemical control, including mechanical or even manual control.
But could weeds develop resistances to these control methods too? It’s possible — and it’s happened before. Case in point: Barnyardgrass has been identified in China that resists hand-pulling by mimicking rice until it's too late to pull. This was after 300 years of evolutionary selection, and 300 years of manually pulling barnyardgrass from rice paddies. In other words, life found a way.
However, evolutionary selection can happen much faster — as growers have found with resistant weeds in Australia, according to a conversation at a recent Glyphosate-Resistant Palmer Amaranth Management Field Day with Bhagirath Chauhan, associate professor at the University of Queensland’s Centre for Crop Science.
One of the newest mechanical tools in weed management toolbox, the Harrington Seed Destructor, originated in Western Australia, where weeds like wild oats, ryegrass, wild radish and wild turnips have developed resistance to multiple herbicide modes of action.
The Destructor collects weed seeds at the time of grain harvest. It doesn’t grind or crush weed seeds, but destroys them through a series of high-speed impacts, rendering them impotent. For some growers in Australia, it’s becoming a big part of integrated resistance management, and it’s piqued the interest of several researchers in the U.S.
But even with mechanical control, certain weeds can develop resistance over time. Take, for example, wild radish, a problem weed for growers in Western Australia.
Recent research at Western Australia shows that while harvest weed seed control is an effective method, offering diversity from chemical control, it also depends on the machine’s ability to collect weed seeds at the time of grain harvest.
In some populations, this research shows the evolution of earlier flowering biotypes. Wild radish plants can drop seed earlier, prior to harvest, when machines like the Destructor would normally collect those seeds.
Here’s the scary part: Within this select population, it didn’t take long — about four or five growing seasons, according to Chauhan. In his words, “It’s not only herbicides you need to rotate.”
That’s why mechanical control, like other methods of control, is considered one of “many little hammers,” or part of a larger integrated resistance management approach. The term is used to describe how many approaches, although not as effective as chemical control individually, are an effective weed control method when combined. It takes all of them to effectively manage resistance. But relying on one single method repeatedly, whether chemical, manual or mechanical, will ultimately result in resistance over time.