agriculture – Conservation Sense and Nonsense

Finding the middle ground between competing conservation strategies

Today Million Trees strays off its well-worn path of informing readers of specific projects in the San Francisco Bay Area that destroy our urban forest and spray our public lands with herbicides. Under the guidance of Charles C. Mann’s latest book, The Wizard and the Prophet (1), we’ll take a detour into the philosophical tenets of conservation. There are competing visions of the future of humans on Earth and they are instrumental in producing different conservation strategies.

We begin by introducing Charles C. Mann because his previous books are essential to our understanding of ecology. His 1491 informed us that the New World “discovered” by Columbus was not the pristine landscape that modern-day native plant advocates are attempting to re-create. Rather it was a land that had been radically altered by indigenous people who had lived in the Western Hemisphere for over 10,000 years. The landscape had been extensively gardened for food production. The large animals had been hunted to extinction. The landscape in the West and Midwest was dominated by open grassland because it had been regularly burned, preventing natural succession to shrubs and trees.

Native Americans setting grass fire, painting by Frederic Remington, 1908

Early explorers carried diseases to the New World to which they were immune, but the native people were not. By the time settlers arrived two hundred years after early explorers, most of the native people had died of the diseases introduced by the explorers. Populations of bison and other grazing animals exploded when those who hunted them were killed by disease. The grazing animals maintained the open grassland that had been created by the fires of the hunters. Archaeological research has only recently revealed the extent of native populations throughout the New World.

Charles Mann’s second book, 1493, reported the global exchange of plants and animals between the New and the Old Worlds that fundamentally altered both worlds. The extent and long history of that exchange makes it impossible for us to see those introduced plants, animals, objects as foreigners who “don’t belong here.”

Different visions of the future

Million Trees is indebted to Charles Mann for the books that are the foundation of our cosmopolitan viewpoint of the world. Mann’s new book, The Wizard and The Prophet is equally important because it helps us understand the interminable debate about conservation. There is a dark view of the future of the environment that predicts nothing but doom and gloom. Extinctions dominate their predictions of the future and humans are seen as the destroyers of nature. The more optimistic view of conservation predicts that the Earth will survive the changes made by humans because humans are capable of innovating to avoid the doom predicted by the pessimists.

Mann describes these contrasting views through the lives of two 20^th Century men whom he calls the prophet and the wizard. The prophet is William Vogt, who believed that the growing population of humans threatened the future of the Earth. The wizard is Norman Borlaug, who won the Nobel Prize in 1970 for developing more productive agricultural crops, collectively called the “Green Revolution.”

The prophet believed that the resources needed to sustain life on Earth are finite and the human population was quickly reaching the point at which sources of food, energy, and water would soon be exhausted, threatening all life with extinction. The wizard devoted his life to expanding food resources to feed the growing human population. These viewpoints are inherently contradictory because making more food available enables more people to survive and increase human populations. Vogt tried to cut off the sources of funding for the agricultural projects of Borlaug.

Different conservation methods: Food

Mann applies these different viewpoints to each major resource issue to explain why the pros and cons of different approaches to conservation are debated, beginning with food production. The Green Revolution occurred in the 1960s when subsistence crops such as wheat, corn, and rice were improved using breeding techniques. Borlaug developed a variety of wheat that was both resistant to stem rust, its most persistent enemy, and produced more wheat for harvest. Working in a desperately poor part of Mexico, with inadequate resources, Borlaug spent 15 years combining thousands of different varieties of wheat to find the winning combination. His work was done prior to our knowledge of DNA and molecular analysis, so it was a process of trial and error. It is a heart-wrenching story of brute labor in extreme conditions. The story is important to our understanding of genetic modification because it reminds us that genetic modification is as old as agriculture itself, although it was called “breeding” until we learned what we now know about DNA.

Mann visits some of the many modern methods of genetic engineering, such as the attempt to “revise” photosynthesis to enable plants to store more carbon, use less water, and tolerate higher temperatures. These projects are controversial with the public, who are deeply suspicious of all genetic engineering. In 1999, about one-quarter of Americans considered genetically modified organisms unsafe. Sixteen years later, 57% of Americans said GMOs are dangerous.

The debate about the value or risks of GMOs is an example of the competing visions of conservation. The prophets see risk and the wizards see opportunities. Surely, there ARE risks, but do they outweigh opportunities? That is the middle ground in the debate. Mann departs from his neutral stance to take a position on GMOs. He quotes many scientific sources in support of his opinion that there is far more opportunity than risk in genetic engineering. My personal opinion is that GMOs are being unfairly judged because of the development of seeds that enable the indiscriminate use of pesticides. The pesticides are damaging the environment, not the genetically modified seeds.

Update: I sent this article to Charles Mann to thank him for his work and invite him to correct any errors I may have made. He has offered this “tiny clarification:”

“I was actually trying to do something very slightly different. The argument about GMOs is frequently posed in terms of health risks–are they safe to eat? In my view, the evidence to date is overwhelming that there is no particular reason to think that GMO crops pose more dangers to human health than crops developed by conventional breeding. At the same time, there are a host of reasons to think that the now-conventional industrial-style agriculture brought to us by the Green Revolution has problems: fertilizer runoff, soil depletion, the destruction of rural communities, etc. GMOs are often said by advocates of industrial ag to be the only way to keep this system going so that we can feed everyone in the world of 10 billion. If you already think that industrial ag is a big problem, then of course you would oppose a technology that is supposed to keep it going. That seems to me a better, more fruitful ground to argue.” Charles C. Mann

I agree that “industrial ag is a big problem,” and I am grateful for this clarification.

Different conservation methods: Water

The availability of adequate water is a limitation for agriculture that provides another example of competing approaches to conservation. The wizards want dams to control available water and maximize its use for agriculture by storing water during rainy periods and using it during dry periods. They also want desalination plants to convert salt water to fresh water. 97.5% of all water on Earth is salt water. It is not useful for agriculture and it is not drinking water for humans.

Prophets want to tear down existing dams to make more water available for non-human inhabitants of the Earth. They also object to desalination plants because they kill marine life, discharge pollutants, and use a lot of energy. Water conservation is the preferred solution to water shortages according to prophets.

Hetch Hetchy canyon was dammed nearly 100 years ago. The dam is the primary source of water for the City of San Francisco and many surrounding communities. The dam generates the electricity that runs San Francisco’s transportation system without using fossil fuels. Sierra Club and other environmental organizations have sued several times to tear down the dam. Inklein English Wikipedia photo

Different conservation methods: Energy

Energy is required for every human enterprise: heat, cooking, transportation, light, industrial production, etc. Wood was the primary source of energy for thousands of years until coal began to be used in China around 3,400 B.C. Although coal is still used, petroleum began to replace it as the primary source of fuel in the 19^th century. The supply of coal and petroleum was considered finite until recently. Thanks to the wizards, extraction methods have been continuously developed such that the supply is now considered effectively infinite as long as increasingly more destructive methods are used, such as fracking and strip mining.

The prophets want to replace fossil fuels as the primary source of energy because of concerns about climate change and pollution. Although they are supportive of developing renewable sources of energy, they often object to specific projects with side-effects. They object to wind turbines because they sometimes kill birds. They object to large solar farms because they displace wildlife. Their preferred approach to energy is conservation. They want us to learn to live with less energy.

The wizards focus on improving existing sources of energy with fewer impacts on the environment. They envision a massive energy grid that can store and share the power generated by renewable sources so that energy is available to everyone at all times whether the wind blows or the sun shines. The prophets object to such big projects. They want energy to be produced locally and available locally. The Sierra Club is opposed to a California Assembly bill that would create a regional power grid.

Different conservation methods: Climate Change

All of these issues come together when climate change is debated. Wizards are working on geo-engineering approaches to reducing greenhouse gas emissions, such as burying carbon in the ground. Their public policy approaches to the issue are also complex and on a large scale, such as cap-and-trade systems to create a profit-motive for reducing carbon emissions.

Prophets are unwilling to take the risks associated with geo-engineering strategies and they are skeptical that cap-and-trade will be more than a means of avoiding the sacrifices needed to reduce greenhouse gas emissions. The Sierra Club was instrumental in preventing the State of Washington from passing a revenue-neutral cap-and-trade law. The Sierra Club also opposed the recent renewal of California’s cap-and-trade law. Market-based approaches to reducing greenhouse gas emissions may not be the strongest policy tools, but they are the only tools available in the US because there is not sufficient political support for stronger policies. Only 11 states have been able to enact market-based laws, such as cap-and-trade. Sierra Club policies are often far removed from political realities.

Unintended consequences

Charles Mann does his best to avoid choosing a side in these debates and on the whole he succeeds. He wants readers to understand that for every conservation method there is a cost and he dutifully tells us about the horrifying consequences of rigidly following one path rather the other.

Vogt, the prophet, firmly believed that the Earth and its human inhabitants would only survive if humans would voluntarily adopt public policies that would limit the growth of human population. This goal was not popularized until The Population Bomb was written by Paul Ehrlich and published by the Sierra Club in 1968. Mandatory population control became the official public policy in Mexico, Bolivia, Peru, Indonesia, and especially India. In the 1970s and 80s millions of women were sterilized in India, often against their will. In China the one-child policy adopted in 1980 forced tens of millions of abortions, many of which killed mothers. Birth control was forced on women in Egypt, Tunisia, Pakistan, South Korea and the Philippines.

There is constant pressure within the Sierra Club to adopt an anti-immigration policy. The Club had such a policy until 1996 and there have been several attempts since to reinstate that policy. I digress to express my personal opinion that immigration is not a legitimate environmental issue because the environment is global. The migration of people from Central America to North America does not fundamentally alter the impact on the environment. If migrants have better access to birth control and education for women in North America, the size of their families would likely decrease.

The Sierra Club, like most mainstream environmental organizations, is firmly in the camp of the prophets. They cast humans as the enemy of nature and their policies reflect their misanthropy. They oppose every housing development project and all recreational access to public lands in California.

The Green Revolution and the way of the wizard carries its own baggage. The new crops and the resources needed to produce them were not equitably distributed in the places where they were needed the most. The richest farmers and biggest land owners in both India and Mexico were the primary beneficiaries of the improved agricultural methods. But it wasn’t just inequitable distribution that did the most damage. The poorest farmers owned the most marginal land. Improved crops made their land more valuable. It was suddenly worthwhile for land owners to dispossess their tenant farmers. The poorest farmers became the poorest homeless people in the huge cities of India and Mexico.

The Green Revolution also greatly increased the use of synthetic fertilizers that have caused nitrogen and phosphorus pollution from agricultural runoff. And pesticides were another tool of the Green Revolution with their own suite of negative environmental consequences.

Both cases illustrate the important role that governments play in environmental policy. Neither the extreme application of population control methods nor the inequitable distribution of agricultural resources were inevitable. In the hands of competent, democratic government both methods had the potential to improve the well-being of humans without damaging the environment.

The Middle Ground: All of the Above

I see Mann’s book about competing conservation strategies as an endorsement of the middle ground. My own strong commitment to the middle ground probably influences my reaction to Mann’s book. The concept of “population control” is as unappealing to me as some of the geo-engineering projects being developed to address climate change.

“Population control” is antithetical to a free society. The middle ground is universal and free access to birth control, early sex education, and educating women in developing countries. Educating women is the most effective method of reducing birth rates.

2014 UN Human Development Index. Human Development Index map. Darker is higher. Countries with a higher HDI usually have a lower birth rate, known as the fertility-income paradox.

The risks of geo-engineering solutions to climate change are too great to pursue without careful scientific analysis to fully understand the risks before they are implemented on a large scale. Likewise, I am opposed to building new nuclear power plants until and unless we have a safe method of disposing of the nuclear waste generated by those plants.

Ironically, the middle ground is in some sense, the most aggressive conservation strategy because it is ALL OF THE ABOVE. The consequences of climate change are too dire to choose one path and abandon the other. We must carefully go down every path available. We must do what we can to limit the increase in human population—within the constraints of a free society—and we must aggressively pursue the technological innovations that are needed to protect the environment from the activities of humans. We must develop new sources of energy that do not emit greenhouse gas emissions as well as reduce our use of limited resources, such as water and energy.

I conclude with an important caveat. This article does not do justice to Mann’s brilliant book. I have only scratched the surface of Mann’s complex and deeply informed book. Charles Mann made a presentation to the Long Now Foundation in San Francisco shortly after the publication of his book. A video of his presentation is available HERE. The video will help bridge the gap between this brief summary and reading Mann’s important book.

Charles C. Mann, The Wizard and The Prophet: Two Remarkable Scientists and Their Dueling Visions to Shape Tomorrow’s World, Alfred Knopf, 2018

“In Jeopardy: The Future of Organic, Biodynamic, Transitional Agriculture”

We are publishing a guest post by Virginia Daley and Fritzi Cohen of the Fearless Fund. They explain that pesticides used by ecological “restorations” are having a negative impact on organic agriculture.

The ever expanding war on “invasive species” is giving “green cover” to the widespread use of inadequately tested pesticides that threaten the health of the very soil and water that sustain all life.

Wherever man migrated he brought plants prized for food, fiber, medicine and ornament. With world exploration and trade, the exchange of flora and fauna became ever wider, and after 1492, the ecosystems of the continents were transformed.

Importation was encouraged by presidents and agencies such as the United States Office of Plant Introduction. The US Department of Agriculture planted the now vilified kudzu, and tamarisk for erosion control, fodder and other useful purposes. Today, 98% of our crops and many plants we think of as American as apple pie are actually from somewhere else –including the apples in that pie.

At the beginning of the 20th century, however, laws were passed “to protect crops and livestock from the wilds of Nature.” Mid-century, in a climate of war and fear of foreign attack, the theory of invasion biology branded alien species “invaders.”

But all-out war was declared on “invasive species” in 1999 with Executive Order 13112, which authorized billion dollar funds and a massive network of agencies to “rapidly respond” to “alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” The National Invasive Species Council was created, whose co-chairs include the secretaries of Interior, Agriculture, and Commerce, State, Defense and Homeland Security, Treasury, Transportation, Health and Human Services as well as Administrators of the EPA, USAID, and the US Trade Representative. Programs coordinate and collaborate with federal, state, county and environmental organizations with a variety of funding sources. Washington State has one of the most sophisticated invasive species networks, and has cannibalized the commission on biodiversity.

More often than not, this war employs chemical weapons. Mike Ludwig exposes the very cozy relationship among government, conservationists and the biotech industry that manufacture herbicides in the Truthout Special Investigation: The Pesticides and Politics of America’s Eco-War. Pesticide profiteers have been involved in this offensive from the beginning. One might question whether the chemicals are merely a method of combat or motive for the war.

Ecologists have begun to raise objections to this approach. Some point out it is ideology rather than sound science that drives the targeting of certain species. Some reveal that many of these demonized species are not inherently harmful and in fact provide environmental services as water filters, soil cleansers, stabilizers, enhancers, protectors, and air purifiers. Others remind us the real drivers of plant “invasions” are frequently man made: climate change, nitrogen eutrophication, increased ubanization and other land-use changes. Evolutionary biologists warn against shortsightedness: ecosystems are constantly changing. Species and communities naturally come and go.

And, of course, there is the warning against the use of dangerous compounds as a solution to perceived problems. As Timothy Scott writes in Invasive Plant Medicine, “[E]ven if the poisons are carefully applied (and they aren’t most of the time) they eventually contaminate the water, soil and air and enter the food chain, affecting microorganisms up through to our dinner plates.” Furthermore, these costly eradication efforts often fail, affect unintended species, (including nearby plants and bees) and actually create superweeds that then require more and stronger herbicides.

Non-native species have been intentionally introduced to hundreds of millions of acres in the US:

Wheat [from the Near East and Ethiopia] 58 million acres
Soybeans [from East Asia] 76.6 million acres
Sorghum [from Africa] 5.6 million acres
Corn [mostly genetically engineered and therefore from nowhere] 92 million acres.

Yet no one calls these monocultures, pesticide-purged of biodiversity, “invasive.”

Thus the label of “invasive species” is political, not ecological. It masks complex issues of land usage and legal questions. And it is exploited to justify an arsenal of control methods that may indeed cause-not prevent-economic, environmental and harm to plant, animal and human health.

Let’s examine some of the featured invasive non-natives in Washington State:

In his paper, Should we care about purple loosestrife?, Claude LaVoie, professor of Environmental Management at Université Laval, Canada describes a massive media campaign to condemn purple loosestrife and refutes the “science” behind it. He calls the depiction of purple loosestrife in scientific studies “(lacking definition) far removed from that in newspapers (alarming)” describing this plant’s negative impacts on wetlands as “probably exaggerated” and pointing out that of the studies done most were somewhat biased, relied on anecdotal information and were not formally reviewed. He considers only one review to be really impartial, “and this one painted an inconclusive picture of the species.”

Though Washington State requires its eradication, edible garlic mustard contains more vitamin C than orange juice, more A than spinach, and shares the medicinal benefits of both garlic and mustard.

On the Hoh River, Japanese knotweed is injected and/or sprayed with glyphosate and imazapyr in the name of salmon restoration. Despite this righteous intent, we have been unable to find any scientific support for Japanese knotweed’s interference with salmon. There is also an assumption that water quality and the water community are unaffected by chemically laced vegetation decaying on waterbanks. The impact of glyphosate and imazapyr on phytoplankton and marine organisms has never been scientifically examined. On the other hand, the virtues of Japanese knotweed have been ignored. Long planted a along riverbanks for stability and shade, beekeepers value the flowers as an important nectar source when little else is flowering. This plant has been used for centuries as a gentle laxative and is an excellent source of the potent antioxidant resveratrol, and it is now used in treating Lyme disease. It exemplifies Tim Scott’s caution that in attacking “invasives,” we may be “destroying potent medicinal remedies.”

Fritzi Cohen owns Moby Dick Hotel and Oyster Farm on Willapa Bay in Nahcotta, WA. For 20 years, she has been fighting the use of insufficiently studied pesticide combinations sprayed by the state and county that have contaminated her tidal flats and oyster beds in order to eliminate a non-native grass, Spartina alterniflora. This eradication project was based on politics, not science. Dr. James Morris, Director of Baruch Institute of Marine and Coastal Science, has demonstrated that contrary to the claims that this grass harms the ecosystem, it provides economic benefits that outweigh the costs of controlling it. This purge has cost taxpayers well over 25 million dollars, degrading Willapa Bay and certainly not helping the health of the ocean.

Chemical warfare campaigns are being waged against so-called “invasive species” on vast tracts of public, tribal, and conservancy land throughout the country which add to the proliferation of pesticides accompanying agricultural GMOs and habitat restoration.

Whether by drift, seepage, runoff or court order, it is an invasion of chemicals, not plants, we should be worried about. The escalating use of pesticides is putting the future of organic, biodynamic, and transitional agriculture in jeopardy. It looks to us as if this is a war on everything ORGANIC.

It is time to reexamine the underlying assumptions and motivations for the ‘war on invasive species’, consider its collateral damage, and explore creative rather than destructive responses to changes in our environment.

We must rely on science not self-interest in distinguishing harm from hype. And realize that the term ‘invasive’ can be arbitrary, ‘harm’ subjective and ‘safety’ unproven. We must abandon eco-illogical practices that throw precaution to the wind and water and soil and if controls are judged -based on fact not fear-to be necessary, we must use methods that safeguard the environment and all creatures in the food chain.

Short of stopping global trade and travel, preventing new introductions will be difficult at best and without reversing global warming species will be migrating and mutating to adapt to climate change. And we are not returning to some imaginary ‘pristine’ Eden. The genie is not going back in the bottle.

Shouldn’t we embrace the possible benefit of these newcomers: as food, fiber, medicine, biofuel, carbon sequestration, erosion control, coastline protection, new industry?

Before embracing “invasiveness” as a claim to virtue that justifies all means of extermination, perhaps we should reflect on the catastrophic changes following the invasion of the Americas by our own European culture.

Visit fearlessfund.info for details For color pictures of the plants described see: http://www.nwcb.wa.gov/

Virginia Daley, Acting Executive Director, Fearless Fund

Fritzi Cohen, President

We have added bold for emphasis, photos, and links to articles about some of the specific issues. Thanks to Ms. Daley and Ms. Cohen for sharing their concerns with the readers of Million Trees.

Glyphosate (AKA Roundup) is damaging the soil

Glyphosate application, Glen Park, San Francisco.

The use of the herbicide, glyphosate (AKA Roundup) has skyrocketed since genetically modified seeds were introduced which enable farmers to spray their crops with unlimited amounts of glyphosate without damaging their crops. We have been reading with increasing alarm the mounting evidence of the damage that is being done to the environment by this indiscriminate use of glyphosate as well as evidence of the impact on human health. We’ve been holding out for an unimpeachable source to inform our readers of this evidence because our critics often accuse us of being alarmist.

On Friday, September 20, 2013, the New York Times published an article about the damage that is being done to agricultural soil by glyphosate use. When the Times reports on an issue, that information has entered the media mainstream. Here are the issues reported by the Times regarding glyphosate use:

Farmers who do not use herbicides report that their crop is often damaged by aerial drift and water runoff from their neighbors who use herbicides.
“Superweeds” that are resistant to any herbicide are becoming more numerous. Million Trees reported on this issue recently. The reaction of the Environmental Protection Agency to these superweeds was to increase the amount of glyphosate that can be legally used on agricultural crops. This is a very unfortunate response to the problem in our opinion and will surely prove to be self-defeating in the end.
The herbicide binds with minerals in the soil—manganese, calcium, boron, etc.—to reduce run off. The herbicide is competing with the plant for these minerals which the plant needs for its growth. These minerals are also important to human nutrition. If the plant contains fewer minerals, its nutritional value is reduced.
This binding of the minerals in the soil is changing the physical quality of the soil, making it very hard and difficult to cultivate. Farmers report that plowing their fields sprayed with glyphosate has become increasingly difficult. If the roots of the plant can’t penetrate the soil, the growth of the plant is retarded.
The herbicide is killing fungi and microbes in the soil. These plants and creatures also benefit crop plant growth by facilitating the transfer of nutrients from the soil to the crop plant.
Another study reports that glyphosate residues in the food we eat are also interfering with the operation of the microbes in our bodies. Many of these microbes are beneficial to us, especially essential to our digestion. If you have had a course of antibiotics, you may have had the opportunity to experience the discomfort of losing beneficial microbes in your gut. Antibiotics often kill both the bacteria that make us sick and the microbes that are essential to your digestive health.
Most of the genetically modified crops are corn and soy. These crops are widely used as animal feed. We speculate that if these crops are harmful to humans, they are probably also harmful to animals.

The manufacturer of glyphosate, Monsanto, has refuted these observations. You can read the New York Times article if you are interested in their version of the story. We close with the words of a farmer who tried Monsanto’s genetically modified seeds. After several years of spraying his crop with glyphosate he has returned to conventional seeds and he is no longer spraying glyphosate: “Although a neighbor told him that he would go broke growing conventional crops, Mr. Verhoef has no plans to go back to genetically engineered varieties. ‘So far so good,’ Mr. Verhoef said, ‘I’m not turning back, because I haven’t seen anything that is going to change my mind about glyphosate.’” We consider this farmer a more credible source of information than Monsanto.

Wily weeds win the war

Farmers have been battling with weeds since the advent of agriculture, about 6,000 years ago. Most of the weapons used against weeds were mechanical until the last century or so when herbicides became the primary weapon. At the same time that the weapon became more lethal, farming techniques changed to give weeds the advantage. Farms became huge monocultures and crop rotations were abandoned in favor of the most profitable crop.

When weeds evolved defenses against the herbicides, farmers responded by increasing doses and manufacturers created new products to which weeds hadn’t yet evolved resistance. Finally, the use of herbicides skyrocketed when crop seeds were invented that weren’t killed by the herbicides, so that huge amounts of herbicides can be used without killing the crop.

When Roundup with the active ingredient glyphosate went on the market in the 1970s, its manufacturer, Monsanto, claimed that weeds would not be able to evolve resistance to it. And apparently that was initially true until Roundup was used on a huge scale when herbicide-resistant seeds were put on the market in the 1980s. Norman Ellstrand of UC Riverside explains why: “He argues that the reason was that farmers applied glyphosate to relatively little farmland. As they applied it to more and more acreage, they raised the evolutionary reward for mutations that allowed weeds to resist glyphosate. ‘That ups the selection pressure tremendously,’ he said.” *

There are now 24 species of weeds that are resistant to glyphosate and they are rapidly expanding their range in agricultural areas all over the world. In 2012, an agricultural consulting firm reported that 34% of farms in the US had glyphosate-resistant weeds. In the first half of 2013, half of all farms in the US are reporting glyphosate-resistant weeds.

Let’s take another approach

Obviously, we are losing the war against weeds. So, let’s examine the strategy we have been using and try another approach. Weed ecologists are now studying the strategies that weeds have used to cope with the weapons we have been using against them. Here are a few of those strategies:

Some weeds have changed color so that they are indistinguishable from the crop they are hiding in.
Weeds that grew in dry ground, evolved to thrive in wet ground in rice fields that are flooded much of the crop season.
Some weeds became shorter to escape the mowing and harvesting of the agricultural crop.
Some weeds drop their seeds and go dormant before the crop is harvested and create seed banks that can sprout when conditions are more favorable for them.
Parasitic weeds wrap around their host and steal nutrients from them.

Some weed ecologists believe that a better understanding of the mechanisms used by weeds to foil our attempts to control them will enable us to devise better weapons against them. They believe that developing new herbicides and/or using more of them will always be a short-term solution.

For example, David Mortensen of Penn State is “investigating controlling weeds by planting crops like winter rye that can kill weeds by blocking sunlight and releasing toxins. ‘You want to spread the selection pressure across a number of things that you’re doing so that the selection pressure is not riding on one tactic,’ he said.”*

Regardless of what method is used to control weeds in the future, let’s consider the toxicity of the method the most important criterion for judging their effectiveness. Even if it kills fewer weeds, the least toxic alternative is the best alternative in our opinion.

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*Carl Zimmer, “Looking for Ways to Beat the Weeds,” New York Times, July 15, 2013.