Glen Canyon Park and Garlon: Answering Jake Sigg

Recently, several people drew our attention to Glen Canyon and the planned spraying of Garlon 4 Ultra to kill the yellow oxalis flowers there. And someone sent in the notice seen here. Apparently, residents of areas nearby have been understandably upset at City plans for this toxic herbicide in an area that is used by preschools, young hikers and dog-walkers.

Spray posponed to 11-18 Feb 2011


They also drew our attention to Jake Sigg’s defense of Garlon.

Jake Sigg, whom some regard as the doyen of San Francisco’s Native Plant movement, authors a widely circulated email newsletter, Nature News. There’s lots in it that appeals to nature-lovers like us, though not his support of Native Plant restoration with herbicides (and his opposition to immigrants, plant or human).

But in a recent issue, Sigg spoke of those who had launched the opposition to Garlon 4 Ultra in Glen Canyon. “Spurious, damaging information being circulated regarding herbicide use in our open spaces,” he titled it, and went on to say: “Mischievous people–possibly well-meaning, but uninformed–are circulating false information, and they are doing it in schools and pre-schools, whipping up fears that have no foundation.”

As best as we could tell, he made the following arguments:

1. It’s being portrayed as a new threat, while actually during his long career as a City gardener, there were no restrictions on pesticide use.

2.  “Long experience and studies have adequately documented the safety of using currently-allowed herbicides.”

3.  He’s personally used them for over 50 years without affecting his “health, which is good.”


1. We agree Garlon probably isn’t a new threat (and didn’t see anyone portraying it as such).  We don’t know how long it’s actually been used specifically in Glen Canyon, especially prior to the Natural Areas Program (NAP) management of the site. The records of the NAP (obtained under the Sunshine regulations) are patchy and non-specific about where the various chemicals were used. Anyway, that’s beside the point. Asbestos was thought safe for years, but we wouldn’t use it in our homes now.

2.  Studies DON’T actually indicate the safety of using these herbicides. In our post, based on the Marin Municipal Water District survey of all the research on the field, we note that the research on Garlon is incomplete, focused primarily on immediate toxicity. There’s nothing much on long-term exposure. Marin Water doesn’t use it. Here’s what we wrote after going through the chapter on Garlon from the Marin Municipal Water District (MMWD) draft Vegetation Management Plan: “It was a pretty thorough multi-source review of what was known about the chemical, and it clarified the risks: birth defects; kidney damage; liver damage; damage to the blood.” [Anyone seeking further information may wish to read our post or the MMWD’s draft chapter.]

San Francisco’s Department of the Environment San Francisco’s Department of the Environment (DOE) recognizes the danger. It classifies both Garlon and Garlon 4 Ultra as Tier I: Most Hazardous. It’s listed as HIGH PRIORITY TO FIND AN ALTERNATIVE (their caps).  The use restrictions say: “Use only for targeted treatments of high profile or highly invasive exotics via dabbing or injection. May use for targeted spraying only when dabbing or injection are not feasible, and only with use of a respirator.”

[Edited to Add:  Recently, someone forwarded us an email from Dow AgriScience, the manufacturer, responding to a query about Garlon’s use where children play. Dow’s answer was that Garlon was a vegetation management product, “in areas such as wildlife openings, forestry sites, along roadways, in ditchbanks, etc.  It is not a product that is used in residential areas.”]

Garlon (triclopyr is the active ingredient) is a systemic herbicide. It relies on the plant absorbing it, and dying of disrupted growth. The chemical has been found in dead vegetation for up to two years afterward.

3.  As for Jake Sigg’s personal experience? We wish him long and happy years, but note that he is (and was) a healthy grown man when he encountered the chemicals. He wasn’t an infant, a pregnant or potentially pregnant woman. Also, individual constitutions differ in their sensitivity to toxins, and it may be he’s blessed with one that isn’t very sensitive. Not everyone is as fortunate. Nor does his experience speak to impacts on non-humans: dogs, birds, amphibians or larval insects. These populations are especially vulnerable.

The unattributed flyer reproduced in his newsletter didn’t have any “spurious information.” (We haven’t included it here because we don’t know who sent it and haven’t got permission.) All it said was that a Garlon spray was planned, the stuff is toxic, it’s a bad idea in an area used by preschoolers and by dog-walkers, and that people could call the SF Department of the Environment to protest. “If you would like to register a complaint or ask more questions, you  can call SF Parks and Rec’s pesticide office at 415-831-6306 or go to ” it said. The only mistake we saw was a typo which misspelled Garlon as Gabron.


So where’s the false information?

Sigg calls this information “mischievous hysteria” and “groundless.” He considers “it drains staff time and energy from their jobs” and notes the ability to “manage their natural resources … depends in great degree on their ability to employ chemical assistance…”

We hope this note clarifies that the information is not “groundless,” or “hysterical” or “mischievous.” We indicate our sources and our reservations about this (and other) herbicides in use in the NAP. We came to this issue indirectly, via our concerns regarding planned herbicide use in the Sutro Cloud Forest (where the UCSF portion is currently herbicide free though we have heard the NAP portion is not). Our research led to a growing concern with the use of these herbicides, and we would like to see Natural Areas use no Tier I or Tier II herbicides, [i.e. the hazardous and most hazardous ones], even if the cost is that non-native flowers will mix in with the poppies and lupines and coyote bush.


In other communications, the NAP has explained why they must use Garlon. It kills broad-leafed plants, but not narrow-leaved ones like grass or iris. If they used a different herbicide like glyphosate, it would kill the flowering oxalis but also the plants they want to keep. (This doesn’t completely explain why they used a mix of Garlon and glyphosate on Twin Peaks earlier on, but we’ll get to that another time).

[Edited to Add (2): Lisa Wayne, Natural Areas Manager, confirmed they won’t be doing it any more. “The Natural Areas Program will not be combining Garlon and Roundup in simultaneous spraying in the future.”]

The NAP has described the oxalis as damaging to native plants, and in another issue of his Nature News, Jake Sigg attributed the decline of the native plant Miner’s Lettuce to the spread of oxalis and erhata grass. But is it actually true? From our research, oxalis likes sunny spots with warm dry soil, while miner’s lettuce prefers cool damp conditions.

Flowering brilliantly, the oxalis is very visible. Each spring, its yellow flowers are abuzz with bees (both native bumblebees and non-native honey-bees) and fluttering with butterflies. [ETA3: A UCLA profile describes it as “producing copious nectar (escaping through openings to form a nectar pool between sepals and corolla).”  Clicking that link takes you to the PDF file.]  It’s an excellent food resource for insects of all kinds, for the birds that feed on them, and the native rodents (like gophers) that eat its bulbs. The rodents are a foundation species for all kinds of animals and birds, from coyotes to hawks and owls. So oxalis is already part of the ecological food web in our city.

Is trying to wipe out oxalis a worthy (or even achievable) goal when it comes at the cost of using one of the most toxic herbicides the city permits? Both Glen Canyon and Twin Peaks have been sprayed before. Frequently. The oxalis returns. (We’d also like to note that none of our research indicated that triclopyr is a good herbicide against this particular plant.)

Or would we rather live with a plant that plays a role in our ecosystem and dies down in late spring, making way for the burgeoning of the next wave of flowers – the California poppy and the various kinds of lupine?

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7 Responses to Glen Canyon Park and Garlon: Answering Jake Sigg

  1. milliontrees says:

    Wow! That photo of oxalis in Glen Canyon Park is stunning! The native plant advocates think they are going to kill all that oxalis with poison? Surely that’s a futile undertaking and in the process of that futile effort, what else will be killed, maimed, sickened? I shudder to think of the consequences of this misguided effort.

  2. HarryEye says:

    When “nature” folks start arguing for dangerous chemicals, you start to become suspicious about their relationship with the big chemical corporations.
    Why on earth would anyone support the use of these devastatingly dangerous chemicals, and even stoop to trying to damage the credibility of those sounding the alarm? There’s something wrong with this picture.

  3. Pingback: More Garlon for Glen Canyon Park? | Save Mount Sutro Forest

  4. Wendy Poinsot says:

    Garlon is effective on oxalis and other broadleaf weeds like dandelion. Who wants a park full of south african oxalis? Not me. To use Garlon safety you need to have an adequate setback from the creek and other drainages. It would be wonderful to restore a more native plant community to Glen Canyon Park. If it was a just a small area, like my garden, we could just keep pulling the oxalis and replant, but for 30+ acres in Glen Canyon, we unfortunately need to use something that will work. There are time-tested safe methods of applying Garlon to get rid of weeds while allowing subsequent replanting. Garlon-type products are what is added to lawn fertilizer and weed control products that so many people use to control weeds in lawns year after year. Hopefully, one or two applications of Garlon, followed by plantings, will go a long way to controlling the oxalis. In the shade, we could actually replace it with the native oxalis — redwood sorrel.

    • webmaster says:

      Wendy, thanks for your comment. We do recognize some people care more about native vegetation than about toxins. The objective of the NAP is indeed to “restore a more native plant community.”

      But it isn’t “one or two” applications. Between March and October 2010, the SF Natural Areas Program and Shelterbelt Builders (contractors) made ten applications of herbicides in Glen Canyon, mostly triclopyr (Garlon) or glyphosate (Roundup or Aquamaster). And though the area around the creek might not be sprayed, the land slopes steeply and it’s all part of the watershed. Triclopyr remains in dead vegetation for up to two years, and as it decays or dries up and is blown downhill, it could very well get in the water.

      (It’s also true some people do use a lot of pesticides on their lawns; many of them are pretty toxic and not great for the environment or for pets and kids who play on them. In fact, that’s partly where the anti-lawn movement comes from. Some of those lawn pesticides aren’t permitted on city-owned properties in San Francisco, though private home-owners can do as they like within EPA restrictions. SF follows the “precautionary principle” — limit use of toxic chemicals as far as possible. [ETA 22 april 2011: The Huffington Post has a recent article about it: : ])

      And some of us do think the oxalis is pretty, even spectacular.

  5. Pingback: Native Plants, Oxalis and the Futility of Garlon | Save Mount Sutro Forest

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