Twin Peaks, Glen Canyon, Natural Areas, and Imazapyr

We’ve been seeing the new pesticide notices up on Twin Peaks, the ones we wrote about earlier here. So today, when we saw three more (and there may have been others) we assumed they were more of the same.

They weren’t. The weren’t attacking ehrhata grass, they were targeting a whole bouquet of plants: cotoneaster; eucalyptus; pittosporum; French Broom.  And the posts on the steep hillside above the homes of Midtown Terrace carried signs for Imazapyr, the newly-approved pesticide for use in “natural” areas, presumably by the Natural Areas Program. Newly approved by SF’s Department of Environment, that is. The Federal Government approved it a long time ago, along with a number of other toxic chemicals.  It’s a Tier II pesticide, and it’s a replacement for Garlon (which we’ve also written about here), which is Tier I. So that’s an improvement, right?

Marginally. Imazapyr has its own problems. One of the factors the Department of Environment considered in approving it is its use in the spartina extirpation project — where also it has been called into question. (This article on the website, Death of a Million Trees, discusses the spartina project.) Here’s what we wrote about Imazapyr in January 2010 when we first found it being used in Stern Grove:



Imazapyr is sold under the brand name of “Habitat” when it’s for Native Plant Restoration. Its other trade names are slightly less benign: Chopper. Stalker. Arsenal. Assault.

It persists in the soil for up to 17 months. It’s water-soluble, and moves through soil to get into groundwater.  “Traces of imazapyr were detected in the groundwater even 8 years after application,” according to a  study by scientists from the Swedish University of Agricultural Sciences. (Pest Management Science, June 2004.)

It’s a broad-spectrum killer, so it kills most things it hits (except some weeds that have become resistant). It’s also a difficult herbicide to target with any degree of precision.

In fact, some  plants actually push it out, so it gets into the tangled roots below the soil and kills other plants. From the Nature Conservancy’s Weed Control Methods handbook: “… imazapyr may be actively exuded from the roots of legumes (such as mesquite), likely as a defense mechanism by those plants… the ability of imazapyr to move via intertwined root grafts may therefore adversely affect the surrounding desirable vegetation with little to no control of the target species.”

This is the chemical opponents compared to Agent Orange, when the border patrol planned to spray it on tall cane growing along the Rio Grande river. Communities on both sides feared contamination of the water. The plan was suspended.

In people, 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.”

Oh, and Imazapyr is illegal in the European Community.


[Edited to Add (31 July 2011):


  Someone recently sent us this sign   with the comment: “I would like to have no poisons used in the park.” Imazapyr is scheduled for use in Glen Canyon. They also sent a photograph of the area involved with the note: “Because of the placement of the signs, I could not get a good shot of both the sign and the area to be poisoned. So here you have the sign, [and] a side view of the sign in the area …”

The target species this time are fennel and cotoneaster. Fennel is the host plant for the brilliant Anise Swallowtail butterfly. In the last butterfly count (July 2011), butterfly specialist Liam O’Brien wrote that San Francisco might have the highest number of Anise Swallowtails “Seen-in-a-day” in all the counts across the nation. He notes why: “…with 44 hills in San Francisco, it being a hill-topping species, lots of fennel…makes perfect sense.” {Emphasis added.} It’s also listed as a species that commonly attracts native bees in the list published by UC Berkeley’s Professor Gordon Frankie.

Cotoneaster is a flowering plant. Its nectar feeds bees and butterflies. (The list above included it as a species that attracts both honeybees and native bees.) Its berries provide food to birds and animals.

Is it worth using toxins to remove these from the Canyon, which is a haven for wildlife and a play-space for children?


Here on Mount Sutro, we’re currently reprieved from pesticides because of UCSF’s policy of using none in the forest or on the Aldea Student Housing campus. They’ve used no toxic pesticides in the forest since 2008, and in the campus since 2009. Their plan, which we believe is endorsed by the Sutro Stewards, calls for a re-introduction of Roundup (glyphosate-based)  and Garlon (which they mistakenly refer to as a glyphosate-based pesticide, but is actually the even-more-toxic triclopyr). We would guess that if the Natural Areas are using Imazapyr, they would add that to their Arsenal too….

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