The toxic pesticides used by San Francisco’s Natural Areas Program

We are reprinting with permission an article from the Save Sutro website about the pesticides being used by San Francisco’s Natural Areas Program.  The Save Sutro website is a valuable source of reliable information on any topic it covers, but it is especially knowledgeable about the pesticides being used in San Francisco. 


It’s no surprise that people are beginning to associate San Francisco’s Natural Areas Program with pesticides. It’s been using them (if the city’s records are accurate) at an increasing rate.

    • In 2009, it applied Garlon 16 times; in 2010, it was 36 times.
    • It applied Roundup (or Aquamaster, also glyphosate) only 7 times in 2009, but 42 times in 2010.

The Draft Environmental Impact Report (DEIR) on the SF Natural Areas Program is rather coy about pesticides. It doesn’t say how much it’ll use, just that it will follow all the rules when using them. (They actually have a poor track record there, but we’ll go into that in another post. [Edited to Add: We did.]) Today, we want to talk about the pesticides on their list: Roundup or Aquamaster (glyphosate); Garlon (triclopyr); Polaris (imazapyr); Milestone (aminopyralid).

SF’s Dept of the Environment classifies all of these as Tier I (Most Hazardous) or Tier II (Hazardous). There’s no mention of using any Tier III (Least Hazardous) chemicals.


We’ve talked before of Roundup, a Tier II pesticide. We hope that in view of the new research that has been surfacing, SF’s DoE will revisit that classification and consider if it deserves a Tier I rating.

  • heart breaking

    It’s been associated with birth-defects, especially around the head, brain and neural tube — defects like microcephaly (tiny head); microphthalmia (tiny undeveloped eyes); impairment of hindbrain development; cyclopia (also called cyclocephaly – a single eye in the middle of the forehead).

  • Research indicates it kills beneficial soil fungi while allowing dangerous ones to grow.
  • It binds to the soil, and acts as a “chelating agent” – trapping elements like magnesium that plants need to grow and thus impoverishing the soil.
  • It’s very dangerous to frogs and other amphibians, and quite dangerous to fish.

GARLON (Triclopyr)

Classified as Tier I, Garlon is even more hazardous than Roundup. In 2010, NAP used this pesticide 36 times (sometimes in combination with Roundup, which it has said it will no longer do). We’ve written about Garlon before, Garlon in our Watershed — which has more details — and many times since then. In brief, these are the main issues:

  • Garlon “causes severe birth defects in rats at relatively low levels of exposure.” Baby rats were born with brains outside their skulls, or no eyelids. Exposed adult females rats also had more failed pregnancies.
  • Rat and dog studies showed damage to the kidneys, the liver, and the blood.
  • About 1-2% of Garlon falling on human skin is absorbed within a day. For rodents, it’s absorbed twelve times as fast. It’s unclear what happens to predators such as hawks that eat the affected rodents.
  • Dogs may be particularly vulnerable; their kidneys may not be able to handle Garlon as well as rats or humans. Dow Chemical objected when the Environmental Protection agency noted decreased red-dye excretion as an adverse effect, so now it’s just listed as an “effect.”
  • It very probably alters soil biology. “Garlon 4 can inhibit growth in the mycorrhizal fungi…” ( soil funguses that help plant nutrition.)
  • It’s particularly dangerous to aquatic creatures: fish (particularly salmon); invertebrates; and aquatic plants.
  • Garlon can persist in dead vegetation for up to two years.

The DEIR has said that the SF NAP’s phasing out Garlon. We have some doubts; its tree-felling program will be futile without Garlon to prevent re-sprouts.


This is a very new pesticide, and not much is known about it — except that it’s very persistent. SF’s DoE has recently approved it for use as a Tier II hazard. It not only doesn’t degrade, some plants excrete it through their roots so it travels through the environment. We’ve written about this one, too, when NAP recently started using it on Twin Peaks and Glen Canyon. (Actually, NAP had started using it prior to SF DoE’s approval , in Stern Grove and also at Lake Merced in 2009 and some unspecified NAP area in 2008.)

About its impact on people, we wrote: “it can cause irreversible damage to the eyes, and irritate the skin and mucosa. As early as 1996, the Journal of Pesticide Reform noted that a major breakdown product is quinolic acid, which is “irritating to eyes, the respiratory system and skin. It is also a neurotoxin, causing nerve lesions and symptoms similar to Huntington’s disease.”

It’s prohibited in the European Union countries, since 2002; and in Norway since December 2001.

MILESTONE (Aminopyralid)

Milestone is a Dow product that kills broadleaf plants while ignoring most grasses. While the DEIR lists this as a chemical used by the NAP, they actually used Milestone very little (twice in 2010). Fortunately. SF DoE classifies it as Tier I, Most Hazardous. This is even more problematically persistent than Imazapyr; a computer search yielded warnings of poisoned compost.


It seems that this chemical is so persistent that if it’s sprayed on plants, and animals eat those plants, it still doesn’t break down. They excrete the stuff in their droppings. If those are composted — it still doesn’t break down the chemical. So now the compost’s got weedkiller in it, and it doesn’t nourish the plants fertilized with the compost, it kills them.

The manufacturer sees this as a benefit. “Because of its residual activity, control can last all season long, or into the season after application on certain weed species,” says the Dow AgroSciences FAQ sheet.

Nevertheless, after an outcry and problems, Dow AgroSciences has stopped selling Milestone in the UK until it’s figured out.

Note to NAP and SFRPD: Don’t put clippings treated with Milestone in the green bin!


When we first started researching pesticide use in “Natural Areas” (and shocking a lot of people who’d assumed “Natural” meant natural), conspiracy theories arose: The chemicals companies were subverting the decision-makers; Pesticides were being portrayed as ecological, and the marketing machine was convincing them; Maybe there were even payoffs!

We think the explanation is much simpler: Those in charge of the Natural Areas are being asked to do the impossible. They’re given a large area, (ETA: it’s as big as Golden Gate Park but in 32 separate locations) in the middle of a city where conditions don’t even approximate those of the pre-industrial era, and asked to return it to a specific moment in time.

It doesn’t want to go.


Someone described the effort to “restore” the “Natural Areas” to “Native plants” as a constant battle. It is, and here’s why:

  • Stopping natural succession. Some areas are harder than others. Grasslands want to grow shrubs, native or not. Then, in pre-industrial San Francisco, along would come grazing browsing animals, or lightning strikes, or a landslide or two, and the shrubs would lose and the grass would win. Preserving grasslands requires killing the shrubs, and in the absence of animals and fires and landslides, it’s pesticides. Repeatedly.
  • Battling successful plants. And then there are the plants that do want to grow there, that grow there naturally (even if, like many San Franciscans, they’re not from here). These we call invasive, and want to get rid of them. That’s more pesticides. And since the plants are good at what they do, they have to be strong pesticides. Repeatedly.
  • “Invaders” compete with each other. Even if the pesticides clear an area of one kind of “invasive” plant, unless the space is intensively gardened, it’ll be taken over by other “invaders.” More pesticides.

The bison in the room (it’s native, unlike the elephant) is this: Contrary to the belief that Native Plants are so adapted to a particular place that “restorations” can be achieved merely by eradicating unwanted plants — Native Plant gardens need the same kind of maintenance and care as any garden.

Without the Sutro Stewards’ volunteers working there every month or so, the Native Garden on top of Mount Sutro would revert to its natural state: a mix of native and introduced plants. (No pesticides are used in that area, or indeed anywhere on UCSF’s Mount Sutro space. It may be the last pesticide-free wild area in San Francisco.)

Is the Natural Areas Program, as it’s currently managed, worth it? We think not, because of:

  • the ongoing and growing need for toxic herbicides;
  • the destruction of habitat for insects, birds and animals that rely on it (and this includes native species, most of which have adapted to introduced plants);
  • we think it’s an expensive misdirected effort in terms of time and treasure.

It makes sense to define small areas as Native Gardens, focus on those, and make them succeed. That can be done — as the Native Garden on Mount Sutro proves — without toxic chemicals.

5 thoughts on “The toxic pesticides used by San Francisco’s Natural Areas Program”

  1. a good article.
    so for people to make a natural area they have to use very unnatural methods.
    nature does not discriminate and does not think like humans. they do not see borders. once all the animals did move free from one place to an other taking with them seeds.
    Webmaster: The animals may not be moving as freely as they once did, but they are still moving the seeds around. My oak tree is having a big acorn year and the squirrels are planting acorns all over the neighborhood as they have forever.
    a plant grows there where it can grow no matter what nationality the place has.

  2. I would suggest, as someone involved in land management who is forced to utilize herbicides to achieve some goals, that more civic engagement in terms of volunteers showing up to mechanically remove invasive species, is the only way to achieve any of these goals without utilizing herbicides.

    1. There is a third alternative. Before deciding to attempt to eradicate a particular plant, ask yourself these questions: What actual damage is this plant doing? What is this plant contributing to this ecosystem? Which animals are eating or living in it? What other ecological functions is this plant performing, such as providing a windbreak or sequestering carbon. Why is this plant here? Has the environment changed such that this plant is well adapted to this ecosystem? Given those changes in the environment, is it possible to eradicate this plant? Or are we wasting resources and damaging the environment with herbicides pointlessly? When you have answered these questions, perhaps you will decide that there is more harm than benefit in trying to eradicate this plant.

      1. I would suggest encouraging the proliferation of an invasive species, without a natural predator, left unchecked could be disaster to a native plant community. I would also suggest that most native plant communities, particularly those I actively manage in a different forest type, carbon uptake and storage is significantly lowered by the presence, and proliferation of, invasive species.

        It is also pertinent to measure the changes in soil stability and compaction as a result in a shift of riparian plant communities.

        Further, the mechanical removal of invasive species by volunteers not only helps to restore the native ecosystem but also encourages community engagement.

        1. Most of your speculative statements are contradicted by observable experience here in California.
          “I would suggest encouraging the proliferation of an invasive species, without a natural predator, left unchecked could be disaster to a native plant community.”
          Most eradication efforts occur in open space where non-native plants have naturalized since being introduced 200 years ago. No one “encourages” them. Most non-native plants have as many predators as native plants because animals adapt to them quickly. Here in a California, it is a myth that non-native plants have no predators.
          “I would also suggest that most native plant communities, particularly those I actively manage in a different forest type, carbon uptake and storage is significantly lowered by the presence, and proliferation of, invasive species.”
          Carbon storage has nothing to do with the nativity of a plant. Above ground carbon storage is largely a function of biomass. That is, the bigger the plant, the more carbon is stored above ground. Carbon storage below ground is largely a function of soil characteristics. When herbicides are used to kill non-native plants, the soil is damaged by killing the fungi and microbes that are a factor in carbon storage.
          “It is also pertinent to measure the changes in soil stability and compaction as a result in a shift of riparian plant communities.”
          I’m not sure what you mean by this, but this statement is contradicted by the consequences of eradicating non-native plants. When trees are destroyed because they are non-native, the result is often catastrophic erosion because the tree roots are no longer stabilizing the soil. When plants are eradicated and results in bare ground, erosion is the consequence.
          “Further, the mechanical removal of invasive species by volunteers not only helps to restore the native ecosystem but also encourages community engagement.”
          The native plant movement has been very strong in California for over 25 years. The conferences of the California Invasive Plant Council and the California Native Plant Society are typically attended by about 800 people who are engaged as volunteers or employed by the “restoration” industry. There are armies of volunteers working on eradication projects. Yet, after 25 years, there are more non-native plants than there were in the past and more and more herbicide is being used.

          You seem to live outside California. Perhaps your experiences are different, but they are not relevant to California or this blog. We’re done here.

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