Weeds resistant to common herbicides — dubbed superweeds — have spread over 60 million acres of U.S. farmland,1 and the economic and environmental devastation caused the weeds is growing, too. Worldwide, weeds have evolved resistance to 167 different herbicides, and herbicide-resistant weeds have been reported in 93 different crops in 70 countries.2
Scientists are now scrambling to understand how weeds are outsmarting these widely used agricultural chemicals, but it's often said that the spread is due to independent evolution via herbicide selection.
However, researchers writing in the journal Agriculture, Ecosystems & Environment believe herbicide-resistance gene flow may be primarily to blame, calling it an "underestimated and underappreciated" phenomenon.3
Herbicide resistance gene flow may be causing superweeds
Concerns surrounding herbicide resistance increased after the 1990s' introduction of genetically engineered (GE) "Roundup Ready" crops designed to resist glyphosate, the active ingredient in Roundup herbicide.
As farmers used an abundance of Roundup on their fields, neglected other weed control measures and continued to grow the same crops on the same land repeatedly (i.e., monoculture), superweeds spread and flourished.4
"Interest in the magnitude and consequences of intra- and interspecific herbicide resistance gene flow, particularly that mediated by pollen, increased in the mid-1990s with the introduction of herbicide-resistant (HR) transgenic crops," the researchers explained. "During that time, less attention was paid to the movement of HR alleles via pollen or seed among weed populations."5
Simulation models predict, however, that frequent widespread applications of glyphosate and other herbicides facilitate an increase in the frequency and movement of herbicide resistance traits. How this is occurring could be due to the flow of GE herbicide resistance from one plant to another, possibly via the transfer of pollen.
"Once a new HR weed biotype has been confirmed in a jurisdiction, how often have we been surprised at its rapid areawide expansion?" the researchers asked. It turns out, however:6
"In genotypic studies of HR weed populations, the contribution of gene flow to incidence of resistance is frequently similar or greater than that of independent evolution."
It's possible, for instance, that pollen carrying genes for herbicide resistance can fertilize a nearby weed, leading to offspring that carry the herbicide resistant trait.7
"Is it a surprise?" the Guardian noted. "On one level no, gene flow and hybridization are as old as plants themselves. Short of creating sterile male plants, it's simply impossible to stop crops releasing pollen to fertilize related neighbors."8
Farmers using more pesticides to fight herbicide resistance
Farmers are scrambling to find a solution for uncontrollable weeds that have outsmarted these man-made chemicals. The solution from agribusinesses entities is to introduce new GE crops designed to withstand not only glyphosate but also additional pesticides to kill off the weeds glyphosate leaves behind.
Enlist E3 soybeans, made by Corteva Agriscience, a division of DowDupont and seed company MS Technologies, is one of the latest, designed to tolerate glyphosate, glufosinate (another herbicide) and 2,4-Dichlorophenoxyacetic acid (2,4-D), one of the ingredients in Agent Orange, which was used to defoliate battlefields in the jungles of Vietnam, with horrendous consequences to the health of those exposed.
"The U.S. Department of Agriculture estimates that by 2020, the use of 2,4-D on America's farms could rise between 100 percent and 600 percent now that it has been approved as part of Enlist Duo," the National Resources Defense Council (NRDC) stated.9
This is concerning because the International Agency for Research on Cancer (IARC) ruled 2,4-D a possible human carcinogen in 2015, and there is concern it may increase the risk of Non-Hodgkin lymphoma and soft-tissue cancer known as sarcoma.
Another example is Roundup Ready Xtend cotton and soybeans, which are GE plants designed to tolerate both glyphosate and dicamba, a highly volatile herbicide known for drifting and damaging off-target crops, including trees.
It's not only weeds that are developing resistance to herbicides, either. Bacteria that have been exposed to Roundup, dicamba and 2,4-D develop resistance to antibiotics 100,000 times faster than the same bacteria that have never been exposed to the herbicides, University of Canterbury has found.10
Herbicide resistance gene flow via pollen
A study of annual ryegrass revealed just how easily pollen may be facilitating the flow of herbicide resistance genes from GE crops to their neighbors. "The transfer of herbicide resistance genes by pollen is a major concern in cross-pollinated species such as annual ryegrass," the researchers noted.11
In the greenhouse, using favorable conditions for pollination, there was a maximum cross-pollination rate of 56.1%. In a field trial, researchers looked at cross-pollination that could occur in real-world conditions, evaluating distance and orientation to an herbicide-resistant pollen source.
In this case, cross-pollination rates varied from 5.5% to 11.6% in plants adjacent to the pollen source, with rates decreasing in farther away plants. According to the study:12
"This model predicted an average gene flow of 7.1% when the pollen donor and recipient plants were at zero meter distance from each other. Pollen-mediated gene flow declined by 50% at 16.7 m from the pollen source, yet under downwind conditions gene flow of 5.2% was predicted at 25 meters, the farthest distance studied."
Is stopping herbicide-resistant superweeds futile?
If gene flow is causing herbicide resistance to flourish, and the next herbicide-resistant weed is just a cross-pollination away, it could appear futile to stop the spread of superweeds. The featured study suggested, however, that the best mitigation strategy is minimizing weed population abundance and seed bank replenishment in fields and adjacent areas.13
The "weed seed bank" refers to the reserve of weed seeds present in the soil. One square foot of soil may contain thousands of weed seeds, and one of the most effective forms of weed management is eliminating "deposits" to the soil's bank of seeds.14 Some effective, nonchemical weed seed bank management practices, some of which you can use in your own backyard, include:15
- Pull weeds before they set seed and even before flowering, as some weeds can mature seeds from flowers that are pollinated
- Pull creeping perennial weeds before they can form new rhizomes, tubers or other propagules
- Grow crops ahead of weeds, as the crop canopy can overshadow weeds and decrease their ability to form seeds
- Pull large weeds before they flower; pulling the largest 10% of weeds may reduce seed production by 90%
- Mow or graze fields promptly after harvest to interrupt weed seed production
Glyphosate use increasing instead of decreasing
The rise of herbicide resistance hasn't stopped farmers from applying the glyphosate on their fields, despite its dropping effectiveness. In 2016, Midwest farmers used an estimated 188.7 million pounds of glyphosate, a fortyfold increase from 1992, and the Midwest accounts for 65% of the total glyphosate usage in the U.S. Some states have seen an even greater increase.16
In Nebraska, Indiana, Illinois, Minnesota and Iowa, glyphosate usage was about 80 times greater in 2016 than in 1992, and 15 times higher than in 2000. According to a 2018 glyphosate market report, the glyphosate market is also predicted to continue growing, potentially doubling by 2021, from the current $5 billion per year to as much as $10 billion.17
The overreliance on glyphosate is already implicated in herbicide resistance, and with increasing applications the problem is slated to worsen. Writing for the Midwest Center for Investigative Reporting, Christopher Walljasper and Ramiro Ferrando point out:18
"Once thought of as a miracle product, overreliance on glyphosate has caused weeds to grow resistant to the chemical and led to diminished research and development for new weed management solutions, according to Bill Curran, president-elect of the Weed Science Society of America and emeritus professor of weed science at Penn State University.
'We're way overreliant on roundup,' Curran said. 'Nobody thought we were going to be dealing with the problems we are dealing with today' … James Benham has been farming in Southeast Indiana for nearly 50 years. Benham said, as resistance grew, Roundup went from a cure-all to a crutch. 'Sometimes if you timed it just right, you could get away with just one spraying. Now we're spraying as often as three or four times a year,' he said.
Benham said farmers continue to spend more on seed and chemicals but aren't seeing more profit. 'That puts the farmer in that much more of a crisis mode. Can't do without it, can't hardly live with it,' he said. As glyphosate became less effective, farmers also turned to even more pesticides to try and grow successful crops each year."
More pesticides is not the answer
Adding more pesticides will only worsen the problem of herbicide resistance, according to the Union of Concerned Scientists, which notes, "Rather than delaying resistance, the use of multiple herbicides would lead to the quicker evolution of weeds that have multiple resistances."
These weeds would be a "nightmare scenario for farmers."19 What's more, the development of more GE crops designed to resist more herbicides is only adding to the issue that triggered the superweed problem in the first place.
The long-term solution lies with adopting regenerative, biodynamic farming principles that don't rely on GMOs and their related pesticides. According to the Union of Concerned Scientists:
"Recent studies have shown that herbicide use could be reduced by more than 90 percent — while maintaining or increasing yields and net farmer profits — through practices based on the principles of ecological science that reduce weed numbers and growth.
These practices include crop rotation (alternating crops from year to year), the use of cover crops and mulches, judicious tillage, and taking advantage of the weed-suppressive chemicals produced by some crops and crop varieties.
Even the use of composted livestock manure and crop residues rather than synthetic fertilizers can help to control some weeds, as these methods generally release nutrients more slowly, which can favor the growth of larger-seeded crops over small-seeded weeds.
These agroecological methods have other important benefits, such as increased soil fertility and water-holding capacity, [and] reduced emissions of water pollutants."
To be part of the solution, seek out non-GMO, organic foods as much as possible, and support farmers who are using regenerative and biodynamic farming principles instead of chemical pesticides.
Source: mercola rss