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Book Review: American Farming Faces a Risky Future
Stahlman is not alone in making this observation. Today, mounting evidence suggests that temperatures of around 90 degrees Fahrenheit or above can make some herbicide-resistant weeds even more resistant, and cause other weeds to be less sensitive to certain chemicals.
Some farmers say they know high temperatures can mess with some herbicides, so they try to avoid spraying in the heat of the day. “A good rule of thumb is if it’s 85 to 90 degrees Fahrenheit, just don’t spray,” says Curt Gottschalk, a farm manager in Hays, Kansas.
Not all experts agree that this pattern, largely demonstrated in lab experiments, poses a problem for farmers. And some herbicides appear to work even better at high temperatures. But if heat is boosting many weeds’ resistance to major herbicides, the implications could be significant. Left unchecked, weeds can devastate harvests and income — if farmers didn’t make an effort to control weeds, they could wipe out around half of all corn and soybean yields across the U.S and Canada, according to the Weed Science Society of America, a nonprofit society of academic and industry scientists. The loss could cost farmers around $43 billion annually.
Farmers are already battling against epidemics of weeds that have developed genetic resistance to multiple herbicides, including glyphosate and dicamba. Stahlman and other weed researchers argue that temperature could be an overlooked second factor strengthening weeds’ defenses against herbicides. Although most farmers now understand that temperature affects herbicides, to the untrained eye it could look just like herbicide resistance, Stahlman says.
These researchers also fear the issue could worsen in the future as climate change raises temperatures and extreme weather events, including heat waves, become more frequent.
“We already know that herbicide resistance is the most problematic issue in chemical weed control,” Maor Matzrafi, a weed scientist at Israel’s national Agricultural Research Organization, wrote in an email to Undark. “Maybe reduced sensitivity due to climate change is next in line.”
Farmers used to rely less on herbicides, instead controlling weeds using laborious methods such as tilling and manual removal. But, starting in the mid-1990s, biotechnology companies began debuting genetically modified crops that were resistant to common, powerful herbicides. The new seeds allowed farmers to liberally spray their fields with agrochemicals to kill weeds while their GM crop flourished. The technology made most manual weeding unnecessary, and herbicide use surged globally. But weeds evolved in response, and herbicide resistant varieties emerged. That has set off a new battle between farmers and weeds, with farmers increasingly using combinations of chemicals, as well as additional doses, to try to knock off weeds.
After Stahlman’s experience with kochia weeds, though, he began to examine whether temperature could be affecting herbicide performance more than was widely recognized. (Stahlman, like many academic weed scientists, has received research funding from agrochemical companies in the past.)
To decipher how heat helps weeds fend off herbicides, Stahlman teamed up with KSU colleagues Mithila Jugulam, a weed physiologist, and Junjun Ou, a research assistant. The team grew seedlings from kochia populations that originated in Kansas, in chambers kept at temperatures ranging from 63.5 to 90.5 degrees Fahrenheit — representative of the state’s spring and summer daytime heat. The temperature in the chambers dropped every 12 hours to mimic cooler nighttimes. When the seedlings reached around 4 inches high, the researchers dosed some with glyphosate and others with dicamba. At weekly intervals, the team examined the weeds for signs of injury. After one month, they cut down the weeds and dried and weighed them.
The team found that, at high temperatures, they needed more than twice the amount of glyphosate and dicamba to control weeds. They published their results in 2016.
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原文来源：https://undark.org/2020/12/07/will-rising-temperatures-make-superweeds-stronger/
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