Mt Davidson: Toxic Garlon, Felled Trees

On a recent trip to Mount Davidson, a visitor saw that Garlon had been sprayed on oxalis.

The Natural Resources Department (NRD, formerly Natural Areas Program) is the most frequent user of pesticides in San Francisco Recreation and Parks Department (SFRPD).  It applied herbicides on Mt Davidson 8 times in 2016. Other SFRPD units have all but stopped using herbicides.

Notice of Garlon 4 Ultra on Oxalis on Mt Davidson, San Francisco CA

Garlon 4 Ultra on Oxalis on Mt Davidson, San Francisco CA

The Natural Resource Department (NRD, formerly Natural Areas Program or NAP), observed the SF Department of the Environment guideline to use blue dye with its herbicides (so people can see and avoid those areas).

Blue dye indicates Garlon 4 Ultra on Mt Davidson Jan 2017

Blue dye indicates Garlon 4 Ultra on Mt Davidson Jan 2017

Unfortunately, they flouted the SF Environment guideline that says there should be no herbicides used within 15 feet of a trail. “Blue dye is right next to and on the trails…” said the visitor.

(Edited to Add: We subsequently learned that SFRPD got a special exemption to permit them to spray on the trail, and they were supposed to have blocked the trail to visitors.)

Here’s a picture of blue dye on the trail.

Blue dye shows Garlon on the path on Mt Davidson, Jan 2017

Blue dye shows Garlon on the path on Mt Davidson, Jan 2017

Garlon by the trail on Mt Davidson, San Francisco, Jan 2017

Garlon by the trail on Mt Davidson, San Francisco, Jan 2017


The SF Department of the Environment (SF Environment), which is responsible for the Integrated Pest Management guidelines, lists Garlon 4 Ultra as a Tier I chemical, Most Hazardous. Ever since we started following this issue, it’s been on the list with a bold, capitalized statement: HIGH PRIORITY TO FIND AN ALTERNATIVE.

Garlon is also supposed to be twenty times as toxic to women as to men. (See page 28 of this California Native Plant Society Presentation which discusses best management practices in herbicide use: Law_Johnson 2014 presentation toxicity )

An article on, based on a detailed study by the Marin Municipal Water Department, describes some of the issues with Garlon:

  • 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, its 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.

parent and child with oxalisThis highly toxic chemical is used by NRD against oxalis during its flowering season – in winter and spring. On Mount Davidson, they used it in February  and December 2016 as well.

It doesn’t make logical sense. Here’s our article on Five reasons it’s okay to love oxalis and stop poisoning it.


Meanwhile, another visitor sent us a series of pictures showing trees being felled at the southwest end of the forest.

tree-noticed-to-be-removed-mt-davidson-jan-2017 tree-x-ed-out-jan-mt-davidson-2017 former-trees-mt-davidson-jan-2017.





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4 Responses to Mt Davidson: Toxic Garlon, Felled Trees

  1. Michael Zanoni says:

    What a strange situation we live in this beautiful city, where there is plenty of money to spray toxic pesticides and cut down beautiful trees yet little or nothing is done to address so many other problems that one of the wealthiest cities on the planet refuses to address. There is almost no traffic enforcement make it dangerous to walk and be a driver for that matter and absolutely nothing is being done to stop noise pollution by the beeping early morning garbage truck carnival where I live at least and the endless roar of motorcycles and there gangs setting off car alarms and breaking windows as they travel through the neighborhoods. The wild west we are again!
    But the sheriff has plenty of energy to poison and destroy the beautiful trees in this park! Very interesting and sad at the same time.

  2. tstar says:

    I am a native San Franciscan who grew up here chewing on the stems of “sour grass” – and I taught my children and grandchildren to do the same. To use any herbicide near it – much less ON IT – is criminal. I urge you to see to the discontinuance of this practice immediately – it is HAZARDOUS.

  3. says:

    What can we do about this??

    [SFForest: We are trying to fight it. We have an appeal in to the Board of Supervisors.
    The hearing date is Feb 28, 2017 at City Hall.]

  4. Paula Bennett says:

    I grew up on Mt Davidson which was our backyard. We ate sourgrass all the time; the idea that it is a problem is absurd. But more importantly, that they plan on cutting down thousands of Eucalyptus is beyond my comprehension. Are they planning on making an amusement park out of the mountain? After coming back to Mt Davidson a few years ago, I heard absolutely no birds anywhere. As a child I heard them every day on Molimo Drive. I am sick to hear of what is going on in this what once was my city, and my mountain. I cannot come to your meetings, but please tell me how else, donations, etc, I can help. THANK YOU!

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