Superweed Saga: Australia’s Creative Tools to Fight Herbicide-Resistant Weeds

Superweed Saga: Australia’s Creative Tools to Fight Herbicide-Resistant Weeds

. 5 min read

Once Upon a Time All Food Was Organic

Although people have indirectly modified plants for thousands of years through artificial selection and domestication, the direct genetic modification of crops in the 1990s revolutionized agriculture. Before this, farmers around the world had been using herbicides to control unwanted plant growth. The most popular of these was Roundup, a highly effective herbicide produced by a subsidiary of Bayer formerly known as Monsanto. Roundup was particularly efficient because of its active ingredient—glyphosate.

Glyphosate was too effective though: a non-selective herbicide, it killed almost all plants by blocking the shikimic acid pathway. For farmers who needed their crops to survive, glyphosate was a risky option.

That changed in 1996, when the first glyphosate resistant crops were put on the market. It seemed ideal: farmers could use Roundup and other herbicides to eliminate weeds without endangering their produce. It could even lead to less pesticide usage overall, because one round of Roundup would get the job done.

For the first few years, farmers had a leg up on insects and weeds without having to destroy their crops, and consequently yields increased immensely. As threats to food security worsened and the rise of large environmental changes like desertification made arable farmland less abundant, maximizing crop yields became an integral part of staving off hunger and preserving the agricultural economy.

In addition to yields, herbicide-resistant crops provided other benefits, such as increasing the viability of no-till farming. Tillage—the annual turnover of soil, usually aided by machine, was historically considered a fixed part of the planting process necessary to incorporate topsoil and break apart weed root systems. But herbicide-resistant crops obviated that need. Tillage increases the risk of erosion and labor costs, so the emergence of no-till farming also contributed to the maximization of profit and a decrease in environmental damage.

Herbicide-resistant crops also reduced fuel consumption. From 1996 to 2009, the United States reduced fuel usage in tillage by 835 million liters, or a reduction of more than 2 billion kilograms of carbon dioxide.

Attack of the Superweed

Problems began to emerge when the glyphosate-resistant crops cross-pollinated with nearby weeds, spreading the resistance trait. These herbicide-resistant weeds, known as superweeds, contaminated fields, creating a feedback loop wherein farmers were forced to use ever harsher herbicides to beat back increasingly stronger weeds.

A 2013 survey found that almost half of U.S. farms had glyphosate-resistant weeds that were spreading exponentially; there are now more than 20 weed species that are resistant to glyphosate. This was especially true for mass-cultivated, economic cornerstone crops like cotton and soybeans: More than 90 percent of fields of those two crops are facing an onslaught of superweeds.

The rise of superweeds was also hastened by monocultural farming practices, wherein the same crop is grown in the same place year after year. Monoculture gave weeds time to “learn” how to compete with specific crops, such that the variations best adapted to certain crop species flourished and became more threatening.

A Mutating Problem

Superweeds pose a long list of potential threats. First, they nullify the benefits of herbicide resistant crops, as they are worse than the weeds farmers  initially sought to eliminate. As fields are overrun with superweeds, yield increases and profit gains disappear.

Glyphosate’s increased usage resulting from crop resistance also poses health risks. In a series of independently conducted studies, glyphosate has been shown to be carcinogenic to people; most studies which conclude differently have been tied back to the industry.

Additionally, there are wide-reaching environmental ramifications. Superweeds don’t just threaten crops, they also have the potential to outcompete other plant species. This can devastate local biodiversity and ecosystems as food chains are destroyed from the bottom up.

Finally, infested fields become useless to farmers, encouraging continual outward expansion of farmland. This results in habitat encroachment and unsustainable land usage, exacerbating the effects of other unsustainable practices like slash-and-burn agriculture.

Searching for Solutions

The classic solution to adapted weeds, super or otherwise, is crop rotation, the practice of regularly changing which crops are grown where in order to distribute nutrient usage, increase soil fertility, and decrease erosion.

But crop rotation, although historically favored until the dawn of the GMO age, typically doesn’t work without an existing market for the crops in rotation. Farmers simply lack the short term economic incentives to ditch the cash crops for less profitable but environmentally beneficial crops like oats or alfalfa. Facing extreme short-term stresses like seasonal weather shifts and blights, it is difficult for many farmers, especially family or small-business farmers, to consider long term solutions which could bankrupt them in the short term.

Another “solution” includes developing crops resistant to even more harmful herbicides. For example, herbicides such as Dicamba and 2,4-D are associated with non-Hodgkin's lymphoma in farm workers. Crops resistant to these herbicides would encourage more liberal use, which is dangerous to not just the farm workers but also to their local communities and other crops because the herbicides spread when blown by wind. Continuing the race for increasingly resistant crops would merely create weeds also resistant to those herbicides, which would accelerate rather than mitigate the superweeds dilemma.

Budding Hope

Australian farmers and scientists have teamed up to take on the superweed problem. Western Australia is considered the superweed capital of the world. Regionally low rainfall limits crops besides barley and dryland wheat, which are primary Western Australian exports. Dense ryegrass weed growth, aided by resistance to traditional herbicides, threaten these exports. In response, Australian farmers have developed a range of solutions that have global potential.

One idea, advocated by the Australian Herbicide Resistance Initiative (AHRI), is mixing and rotating different weaker herbicides: using different combinations of the chemicals and switching them up annually. AHRI modeled different strategies, and found that herbicide rotation alone worked in the short term, but didn’t prevent herbicide resistance in weeds in the long term. Purchasing a mix of herbicides however, can be more expensive than single herbicides.

Another solution Australian farmers have found is Harvest Seed Weed Control, which over 80 percent of Australian farmers expect to use in the foreseeable future. The main goal of Harvest Seed Weed Control is capturing and destroying weed seeds, so that they can’t spread.

A widely used seed control technique known as narrow-windrow burning involves concentrating and then burning chaff in a narrow windrow—a line of grain drying in the wind. The burning process kills the vast majority of weed seeds. Other strategies, known as chaff tramlining and chaff lining, are similar in concept: weed seeds are concentrated in lines so they don’t contaminate the crops.

These strategies are non-herbicidal ways to prevent superweed encroachment, constraining the viability of the weed seedbank and preventing the weeds from effectively competing.

Herbicides have become an integral and unerasable part of modern farming. The irrefutable benefits they provide for farmers and their reduction of potentially more damaging practices like the burning of fields and forests are integral to modern agriculture. The solution then can’t be to simply stop using herbicides or herbicide-resistant plants.

The progress made by Australia suggests that there is a future of weed management that recognizes the necessary evils of herbicide usage but doesn’t rely on unsustainable and dangerous techniques to preserve agriculture.

Superfood or Superthreat

Superweeds are part and parcel of a larger and increasingly polar conversation surrounding the future of GMOs. After glyphosate-resistant crops came Bt crops, which poisoned insects and predictably resulted in toxin-resistant insects. Now, scientists are expanding from crops to animals: a genetically modified salmon species hit the market recently and livestock modified to be disease resistant are in the works. These animals could create a range of unforeseen consequences, just as genetically modified crops did.

Debates over the safety and even ethicality of GMOs persist. All these suggest that more global regulations on GMOs are necessary. But given a divergent international landscape, it seems unlikely that comprehensive new GMO regulations will appear anytime soon.