Herbicides in San Francisco’s ‘Natural Areas’: 2016 Report

We finally received all the 2016 pesticide use reports from San Francisco Recreation and Parks Department (SFRPD), including of course the Natural Resources Department (formerly the Natural Areas Program). Coincidentally, it’s oxalis season, and by the logic of the NRD – it’s Garlon time. Of which more below.

In April 2016, SF Department of the Environment rolled out its new guidelines for pesticide use. Since then, the other parks sections nearly eliminated pesticides – but not NRD. They reduced their use of Roundup quite drastically (thankfully, since it’s a probable carcinogen). But they increased their usage of Garlon and Imazapyr.


San Francisco Recreation and Parks Department (ex Harding Golf Course, which is under a management contract with the PGA Tour) has all but stopped using herbicides – except for the so-called Natural Resources Department.


nrd-vs-sfrpd-herbicide-application-2016-smLooking at the whole of 2016, SFRPD used pesticides 159 times. Of those, 143 applications were by the NRD.

NRD used more of nearly all Tier I and Tier II herbicides. It used 48% of the total Roundup SFRPD applied; 100% of the Garlon; 100% of the Imazapyr (Stalker, Polaris); and 99% of the Milestone VM.

Excluding for Greenmatch, a herbicide that is considered organic (but still classified as Tier II), NRD used more Tier I and Tier II herbicides than the rest of SFRPD put together. (As usual, we exclude Harding Golf Course, which is under a management contract to the PGA Tour and uses pesticides to maintain tournament readiness.)

The good news is that NRD has succeeded in reducing herbicide use, mainly by cutting back sharply on Roundup. Even if not as much as other SFRPD departments, it’s progress. It is still not down to 2009  or even 2008 levels, but has reduced substantially from 2013, which was peak pesticide for NRD (then NAP).



This year, NRD also started managing – i.e. spraying with herbicides – certain parks belonging to SF PUC:

  • Lake Merced,
  • Laguna Honda, and
  • part of Twin Peaks.

Since they are following the same regimen and using NRD staff, we include the PUC data along with NRD information.


We thought we’d take a look at which parks they treated most often with herbicides in 2016. Bayview Hill was the clear “winner” with 34 applications. McLaren Park was hit 27 times, and Twin Peaks 25 times. Glen Canyon had 10 applications of herbicides, and Mt Davidson was herbicided 8 times.


To return to Garlon, the most toxic herbicide SF Environment allows for use in SFRPD. It’s classified as Tier I (Most Hazardous) and the notation on the list says: Subject to “Limitations on most restricted
herbicides”. 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.

It’s been “High Priority to Find Alternative” in all the years we’ve been studying this issue. Here’s the solution: Stop obsessing over oxalis.

The only current use for Garlon in SFRPD is battling oxalis in “Natural Areas.” It’s been used 23 times in 2016 by NRD – and zero times by all the other departments.

The obsession with oxalis makes no logical sense. Our article Five Reasons it’s Okay to Love Oxalis and Stop Poisoning it points out that:

Honeybee in oxalis flower

Honeybee in oxalis flower

1) It’s already part of the ecological food web in our city, providing nectar to honey-bees, bumblebees, butterflies and other pollinators. Ironically, the pollination doesn’t benefit the oxalis, which doesn’t set seed in San Francisco.

2) It’s good for wildlife, providing food for gophers, a foundation species that in turn feed predators from hawks and owls and herons to coyotes and foxes.

3) The myth is that oxalis leaves the ground bare after it dies down in summer. Actually, it enriches the soil with phosphorus, which benefits the grasslands in which it grows.

4) Oxalis has little impact on native plants. NRD argues that oxalis takes over grasslands and destroys them, particularly the native grasses. However, grasslands in most of California including San Francisco are dominated non-native grasses. The change occurred over 100 years ago, when these grasses were planted for pasture. So the grassland that NAP is defending with herbicides are primarily non-native anyway.

According to a study: “Oxalis is a poor competitor. This is consistent with the preferential distribution of Oxalis in disturbed areas such as ruderal habitats, and might explain its low influence on the cover of native species in invaded sites.
The California Invasive Plant Council rates its invasiveness as “moderate,” considering it as somewhat invasive in sand dunes and less so in coastal bluff areas.
oxalis and california poppies sm
In San Francisco, every place where oxalis grows is already a disturbed environment, a mix of non-native grasses and plants with native plants (some of which have been artificially planted).  Here,  oxalis appears to grow happily with other plants – including, for instance, the native California poppy in the picture above.

5) Kids love it, and it’s edible. Parents know that children will often nibble on “sourgrass” – indeed, so do parents sometimes! Adding toxic herbicides is a poor idea, especially since it is usually applied during the flowering season.

Photo credit: Badjonni (Creative Commons - Flickr)

Photo credit: Badjonni (Creative Commons – Flickr)

So, to summarize:

“There’s no sign that oxalis has a negative impact on wildlife, and plenty of evidence it’s already part of the ecological food web of our city.  The evidence also suggests it’s not having a negative effect on other plants in San Francisco either. Lots of people find this flower attractive; one writer described it as the city smiling with Bermuda buttercups.

In any case, even Doug Johnson of the California Invasive Plant Council doesn’t think it’s worth attacking at a landscape level: the payoff isn’t worth the expense. Removing it from the hundreds of acres in Natural Areas isn’t as simple as eradicating it from a small yard where it’s clashing with the garden design. It requires a lot of work, a lot of powerful herbicides, a multi-year effort – and for what?

The justification for using strong pesticides like Garlon to control it is weak. We call on NAP to stop using Tier I and Tier II herbicides altogether.”


NRD has been trying to reduce the amount of Garlon in each application used by changing to a new surfactant for Garlon: CMR Silicone Surfactant. (A surfactant is a chemical used with a pesticide to make it spread better.)

This is also a dubious chemical.A 2016 NIH paper, Toxicological Risks of Agrochemical Spray Adjuvants: Organosilicone Surfactants May Not Be Safe, suggests that these surfactants have a deleterious effect on bees (which we know visit oxalis), and point out that they are under-regulated:

“Agrochemical risk assessment that takes into account only pesticide active ingredients without the spray adjuvants commonly used in their application will miss important toxicity outcomes detrimental to non-target species, including humans.”

(You can download the whole paper as a PDF here: fpubh-04-00092

Mullin CA, Fine JD, Reynolds RD and Frazier MT (2016)

Toxicological Risks of Agrochemical Spray Adjuvants: Organosilicone Surfactants May Not Be Safe.
Front. Public Health 4:92.
doi: 10.3389/fpubh.2016.00092

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5 Responses to Herbicides in San Francisco’s ‘Natural Areas’: 2016 Report

  1. Morley SInger says:

    Thank you for your well researched and responsible views on oxalis and use of toxic pesticides.
    You must realize that the policies of the NAP are governed by a totally irrational cult-like belief in attempting to replace what currently exists with what they what MIGHT have existed in the distant past. Their policies are a form of “plant racism”- arbitrarily selecting a population to exterminate. They are strongly influenced by a small number of determined individuals with limited qualifications.
    Keep up with your excellent work!

  2. milliontrees says:

    Here’s another reason why it is pointless to spray oxalis with herbicides: “These herbicides don’t kill the bulbs, and regrowth from bulbs should be expected.” This a quote from the UC Davis weed management website about spraying oxalis with Garlon: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7444.html

    Yet another pointless crusade against a harmless plant that is useful to wildlife.

  3. Pingback: Pesticide Usage in 2021: SFRPD Does Better – except for NRD | San Francisco Forest Alliance

  4. Pingback: Pesticide Usage in 2021: SFRPD Does Better – except for NRD

  5. Pingback: Pesticide use in public parks in the San Francisco Bay Area – Conservation Sense and Nonsense

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