When faced with invasive, non-native weeds on the range, the first response for many conservationists is to load up a backpack sprayer full of pesticides.

Spraying chemicals toxic to wildlife and people — under the auspices of protecting wildlife and people — is often portrayed as a necessary evil if we want to stop the spread of invasive species.

But what if such spraying doesn’t actually work?

A 16-year study recently released by the United States Department of Agriculture found that spraying herbicide doesn’t always pay.

The study, on the USDA’s Agricultural Research Station in Miles City, Montana, found that spraying for invasive leafy spurge had quite different results than intended:

“A one-time aerial spraying of herbicide showed that the invasive leafy spurge (Euphorbia esula L) may have ultimately increased due to spraying. Conversely, several desirable native forbs were still suffering the effects of spraying 16 years after spraying.”

This is just one study, of course.

But it begs the question: Should the first impulse of conservationists be to spray herbicides and other pesticides to control invasive species? Are such efforts really working?

Spraying pesticides for invasives control has long struck me as one of those cases where “the cure is often worse than the disease.”

Many pesticides have well-documented negative effects on fish and birds and humans. It would seem that we should apply them judiciously and only as a last resort.

Perhaps the real issue here is humanity’s relationship with non-native species. Too often, conservationists appear content to label all non-native species as “bad” and thus seek to eradicate them by any means necessary.

It’s time to face up to the reality of the “invasive species” issue: It’s complicated.

The rapid spread of invasives may be a symptom of deeper ecological problems, not the problem itself. Thus, using chemicals is only treating the symptom, not addressing the real issues. I’ll refrain from making any comparisons to U.S. health care.

In other instances, invasives may be so established on a landscape that we can only hope to manage them, and eradication attempts will be proven folly.

Complex conservation issues deserve complex solutions. Spraying too often feels reactionary rather than well thought.

Spraying does involve action, and action often gives the illusion of accomplishment. Weeds wilt and die. Maybe they even disappear (for a bit).

All this plays well to the battle terminology often employed in invasives control efforts: Dropping toxic chemicals from an airplane makes a certain sense when we’re “winning the war on weeds.”

Certainly, there are incidences where spraying is effective conservation. In the remote canyons of Hells Canyon, for instance, helicopter surveys can reveal small, new weed infestations.

Here, Conservancy crews spray the weeds before they become established. If those weeds  spread, they would damage wildlife habitat and become almost impossible to control. Thus, by spraying now, there likely will be less need for more spraying later.

That’s strategic. Many pesticide applications in invasives control, I am convinced, are not.

Too often, conservationists have been spraying first, asking questions later.

It’s time we take a long, hard look at our use of pesticides, and quit using them when the only measurable outcome is increasing toxic chemicals in our land and water.

(Image credit: Matt Miller/TNC.)

If you believe in the work we’re doing, please lend a hand.


  1. I agree completely. The weed is there because the natives were disturbed, the niche was open. Spraying just re-opens the niche, without solving the underlying problem. It would be one thing to spray and then follow with an aggressive native recolonization effort, but just spraying simply opens the space for more invaders.

  2. Yes. There’s an unfortunate association between native plant activism and herbicide use, where the measure seems to be resouces input rather than medium- or long-term outcomes.

  3. Don’t you think it’s a bit much to draw such a sweeping conclusion from the results of one study?

  4. You are right, “it’s complicated,” so it’s a shame your article oversimplifies. I understand and empathize with the sentiment. But I think the net is being cast too broadly here, and there’s a fair amount of personal philosophy included. Land managers using herbicides responsibly as one tool in their toolbox already have an uphill battle dealing with blanket condemnation of herbicide use. One of our organization’s goals is to push forward with constructive dialog with other environmental organizations who focus on toxics issues, in order to discern which wildland weed control applications may be inappropriate. I’m convinced that those working on invasive species and habitat restoration are often at the forefront of realizing that issues such as this are “complicated.”

  5. i challenge the claim of “toxic to people and wildlife”. the author obviously does not understand that compounds used by conservation workers are made to work on plant anatomy, not animal. if one researches lab data on these chemicals, it becomes clear that toxicity and persistence are not real issues, but rather hyped through generalizations that people like the author make. two main aspects to bear in mind when judging pesticide use are rate and route of exposure. then please tell me what the exposure level is to “people and wildlife” from low rates of substances that absorb into critical plant anatomy and do not leach into soil or waterways.
    please do a little more homework before writing such an uninformed article, because from 20 years of doing this work i can truly say that judicious use of herbicides IS indeed preventing invasive plants from displacing native habitat.

  6. Please come back to Cape May preserve and respray the phragmites, they are covering the frog ponds on the east end, and marching through the interior

  7. your biased statements about toxicity (of all pesticides) to birds, fish and humans indicates to me (a past pesticide regulator) that you have little to no knowledge of the many environmental fate and toxicology studies required of all pesticides registered for use by the EPA. Its a shame that your organization, which I support, apparently has nobody with any expertise in pesticides to review your articles before they’re printed. Quite frankly, I’d much rather spray an approved herbicide at approved rates, than do a prescribed burn, or mechanically try to destroy invasive plants. Use the wonderful, well researched tecnology that’s available! And stop making sweeping statements that feed on people’s fear of chemicals due to lack of knowledge. Biased writings I can do without!

  8. The annual symposium on “wildland weed management” that will take place in Fresno early in October has always been sponsored by the chemical industry. Take a look at the website. The most generous donors are Dow, Monsanto, and DuPont. Coincidence? I don’t think so.

  9. I certainly agree that it is a mistake to demonize all man made chemicals. Every substance that comes into contact with a living thing has some effect on that organism, however small, and that includes “natural” substances. Man made chemicals are not inherently more dangerous than naturally occuring ones. No matter how heavily studied a medication or herbicide or anything else might be, however, the most we can ever say is that appropriate use of that chemical produces no detectable harm by the measures of the available studies. We do not and will never fully understand all the possible effects of various chemicals on the environment and human health. Whether considering taking a given medication, supplement, or food or applying an herbicide there always has to be consideration of the risk vs. the benefit. We never know all the risks but it is perhaps easier to determine benefit. Maybe the author is simply suggesting that we need to at least be very certain that there are real, long term benefits to offset potential risks before considering use of herbicides. After all, he does seem to support application of herbicides in some situations such as in Hells Canyon so I don’t think the piece is oversimplifying or anti-pesticide in a blanket fashion.

  10. There is no conspiracy of chemical companies versus the environment, Mr, Miller. Businesses are driven by market demand, and their sponsoring the wildland weeds symposium is similar to Microsoft sponsoring a high tech event.

    Does that mean Microsoft is out to turn all into computer drones? The conservation market demands low toxicity weed killers with quick environmental fate, and these businesses are meeting those needs.
    Events like the wildland weeds symposium serve as an educational forum, and from the sounds of your exaggerated article, it appears you could use a little of that.

    i noticed your links on the terror of weed killers all go on to mention only insecticides in their horror stories…the only herbicide briefly mentioned is 2,4-D– which is far from a top choice for conservation managers. You may also need to examine the methods of how these herbicides are being applied….spraying is only one of many types of applications, and most managers use direct application methods that will not harm the resources they are trying to protect. Investigative journalism requires a non-biased view, but something tells me you may be in conspiracy with the Journal of Pesticide Reform.

  11. Thanks all for your comments.

    Pat Bily, just to clarify your comment above: The comment by “MM” above about a wildlands weed conference was not written by me.

    All Cool Green Science bloggers use their full (and real) names in blog posts and responses.

    Thanks again for the discussion.


  12. In response to MM’s post: I am the director of the organization hosting the symposium you refers to. The annual Symposium put on by the California Invasive Plant Council is sponsored by groups that include agencies, NGOs, and companies, some of whom are herbicide mfrs. A list of last year’s sponsors are available at Cal-IPC Symposium Sponsors.pdf. This year’s gold sponsors include US Forest Service, Santa Ana Watershed Association, the California Native Plant Society, and RECON Environmental Consultants. We have 25 sponsors this year, only two — Dow and DuPont — of which are herbicide mfrs, and the are the second lowest level. This hardly qualifies as “the most generous donors.”

    Herbicide mfrs are involved because the make tools that some natural resource managers use in some situations, and it makes sense for conference attendees to have access to information about these products. It is also good for the mfrs to interact with a community that has high standards for environmental safety.

    Invasive species management is a challenging environmental issue in that it makes us face up to the fact that often there are often no simple solutions that don’t involve complex trade offs. The tendency for some environmentalists to adopt a strict purist approach — “you associate with herbicide mfrs, therefor you are not environmentally responsible” — is something we need to work on. We work in coalition with Defenders of Wildlife, TNC and others on invasive species issues here in CA as well as nationally, and certainly engagement of the environmental community, including those organizations focusing on toxics, is a need.

  13. I have absolutely no doubt that this will fall on deaf ears, but invasive species are simply taking advantage of changing conditions of life and thus just demonstrating success in the battle for life. And that means conservationists are specifically targeting success in the battle for life and thus specifically trying to achieve the exact opposite of natural selection, which is utterly ridiculous. (

    1. Exactly, fishSNORKEL! Some McCarthy era Brit named Charles Elton wrote some ranting niche book on “invasive” species (with a vernacular eerily reminiscent of war and intolerance), and suddenly “invasive species” are more important than centuries of Darwin’s teachings about evolution, migration of species, natural adaptation and natural selection. Why? Because it’s a multi-billion dollar market for the Big 6 (now 3) agrichem/herbicide companies. It wasn’t until the 80’s/90’s when herbicide companies seized upon this fringe “thinker’s” (i.e. xenophobe’s) poorly supported hypothesis about the dangers of “invading” *foreign* plants that it became a [pseudo] science. Monsanto, Dow et al poured millions into weed science departments to establish “invasion biology” as a real discipline. It’s not-at best, it’s a social science with racist undertones. Check the history, and follow the money (donations, sponsorships, endowments…). The connection is crystal clear. Invasive species are marketing hype in almost all cases. In some closed ecosystems, introduced species can disrupt the status quo, but it’s not like it’s in a pristine state to begin with. Places like the Great Lakes were likely vulnerable to new species because they were overfished and converted to industry-serving water bodies in the first place. Common sense 101. May all those who continue to strike their Faustian bargains with Mam Monsanto go down in flames with this BS boondoggle land poisoning program.

  14. I don’t think people are aware that pesticides are still really widely used and can cause serious issues.

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