San Francisco Toxic Herbicides Use

The chart above is for Natural Resource Department. This entity manages all the so-called “natural areas” or “significant natural resources areas” in San Francisco. Many people assume that these areas aren’t subject to toxic herbicides. In fact, (with the exception of the Harding Park Golf Course), NRD is the biggest single user of herbicides within San Francisco Recreation and Parks Department.  Hence they’re the biggest concern for residents whose neighborhood parks are designated as “natural” areas.  After a short-lived dip in use in 2014-2016 the amount of herbicides in NRD/PUC parks has risen steadily, and is the highest in 2020 in over a dozen years.


You may not know that San Francisco regularly uses highly toxic herbicides in parks and on watersheds, including Hetch Hetchy, Crystal Springs, and the Alameda Watershed.  San Francisco Forest Alliance tracks pesticide use by SF Rec & Park – and the Natural Resources Department (NRD) – through public record requests.

We learned of herbicide use in watersheds only through attending the Department of Environment and Integrated Pest Management Technical Advisory Committee (IPM TAC) meetings.

[If you regularly walk in a “natural area”, you have seen signs warning of pesticide use. I got a dog in 2000 and walked all around Mt. Davidson and Glen Canyon. That is when I became aware of this issue.  I had no idea about herbicide use in San Francisco before that time. AG]


High toxicity pesticides are bad for the environment and people.

Herbicides are more toxic, more dangerous, more persistent, and more mobile in the environment than their manufacturers disclose.

Roundup, was touted as “safer than table salt” for decades. But in August 2018, in DeWayne Lee Johnson v. Monsanto Company, a San Francisco jury awarded $289.2 million in damages to a former Benicia School District groundskeeper with terminal non-Hodgkin’s Lymphoma.

In March 2019, a jury in a federal court in San Francisco unanimously ordered Monsanto to pay roughly $80 million in damages for failing to warn plaintiff Edwin Hardeman of the cancer risks of Roundup herbicide.

In May 2019, after less than two days of deliberations, a California jury found Monsanto guilty and ordered it to pay over $2 billion in punitive and compensatory damages to a married couple who both developed non-Hodgkin’s Lymphoma they say was caused by their many years of using Roundup products.

In each case the jury determined that the company knew about the carcinogenicity of Roundup and purposely deceived the public.

By now more than 100,000 people have made claims in courts across the country, alleging that exposure to glyphosate-based herbicides led to various types of cancer. And yet Roundup remains on the SF “Reduced Risk Pesticide List,” along with other herbicides, like Garlon 4 Ultra, which are likely even more toxic, but are less researched, since they are less widely used.

There are calls and petitions to ban glyphosate, but banning one chemical would not solve the problem of chemical contamination. Numerous scientific studies associate exposure to herbicides of all kinds with cancer, developmental issues, learning disabilities, nerve and immune system damage, liver and kidney damage, multiple sclerosis, Parkinson’s disease, diabetes, infertility, birth defects, disruption of gut microbiomes, and of the endocrine system.

SF IPM has already hired more people to look for effective glyphosate replacements, and added new high-toxicity herbicides to the “Reduced Risk” list.

Unlike insecticides and rodent control, which are arguably needed to fight disease agents, herbicides are used only on plants, none of which endanger human health, and many of which, in fact, are beneficial to wildlife.


Chemical contamination is dangerous.  Here are just a few examples:


IPM (Integrated Pest Management), Rec & Park, SFPUC claim that:

  • High toxicity herbicides are used “only as a last resort”,
  • They adhere to the Precautionary Principle,
  • There is no other way to manage the land,
  • Managing land without herbicides is too expensive,
  • Herbicides are essential for “sensitive species” & preservation of “biodiversity

None of these myths is true.

Myth: It’s always a Last Resort.

SF Rec & Park used high toxicity herbicides as a “last resort” 295 times in 2020, 243 times in 2019, 223 times in 2018, and 236 times in 2017. How is something a last resort, when it is used 4-5 times every week?

Myth: We follow the “Precautionary Principle”

That would suggest that as a precaution, San Francisco would not use toxic herbicides. Instead, they are classified into three Tiers: Tier III is the least hazardous, Tier II is more hazardous, and Tier I is the Most Hazardous. All of the Tier I and II synthetic herbicides are linked by scientific studies to human health problems, yet they are still used regularly.

Myth: There’s no other way to manage the land:

People are becoming more and more aware of chemical contamination and moving to organic land management.

  • The Marin Municipal Water District has been herbicide free since 2005.
  • Seven out of 11 towns in Marin County don’t use herbicides at all.
  • In a 2017 pilot project, Marin demonstrated that traffic medians could be maintained without glyphosate (the only synthetic herbicide previously used on medians). Marin County will continue to move forward without herbicides on all medians and roadside landscapes.
  • The City of Richmond had completely banned use of herbicides in weed abatement activities by the city or its contractors in 2016.
  • The Town of Fairfax prohibits use of all synthetic pesticides in parks, open space parcels and public rights of way and buildings it owns and maintains, and a neighbor notification is required prior to the use of pesticides on private property.
  • In 2000 the Arcata City Council banned the use of pesticides on all properties owned or managed by the city, by unanimous vote. (The city hadn’t actually used them since 1986.)
  • Non-toxic Irvine, started by parents of kids with cancers, convinced the city of Irvine to switch from regular use of herbicides and toxic fertilizers to eliminating all of them under all circumstances and adopting a completely organic pest-management program. The new program also costs less (even with initial investments in soil augmentation included), and water use was reduced by 30%.

Myth: Managing land without herbicides is too expensive:

In 1986 Arcata’s task force cost analysis compared the use of pesticide application to manual vegetation removal and found that increased labor costs were balanced by decreased costs of purchasing, applying, reporting and storing of the pesticides. According to Dan Diemer, Arcata’s Park Superintendent, “From a management perspective it’s actually easier to not use pesticides. The amount of training and paperwork that is required for pesticide use is intense.”

The city of Irvine found that financial benefits come along with ecological and health benefits from eliminating toxic pesticides from landscaping routines.

Myth:  Herbicides are essential for “sensitive species” & preservation of “biodiversity”:

“Pesticides are made to kill living things, and the idea that they only kill the things they’re intended to is just wishful thinking...” – Jane Goodall.

A 2006 Sharp Park court order prohibited the use of 66 different pesticides because of unacceptable risks to the threatened red-legged frog and endangered California garter snake that live there.

Those chemicals also present unacceptable risks for non-endangered and non-threatened species, including all of us.

In 2015 Harper’s magazine published an article titled “Weed Whackers Monsanto, Glyphosate, and the War on Invasive Species,” wherein it exposes the fact that the story of necessity of eradication of “invasive” plants, in order to save fragile “native” species is to the great extent manufactured by chemical industry.

The public is largely unaware of billions of dollars of taxpayers’ money being wasted on futile attempts to eradicate “invasive” plants.  There is even less knowledge of the quantities of pesticides being used by these projects or the toxicity of those pesticides.

There are numerous examples of “native” species being harmed by herbicides used to presumably help them.

Here “native” oaks and maples were badly damaged (or maybe killed) by eradication of “non-native” plants underneath:  –

Imazapyr, the herbicide mentioned in this article is among those regularly used by the city.


It is known now that “the dose makes the poison” adage is not accurate

Low doses of contaminants in water, food, and environment can have significant chronic effects, if there is a long-term exposure.  Substances cause different effects at different levels and often are endocrine disruptors (EDC) at very low levels.   Many studies show that glyphosate—there are more studies on glyphosate since it is the most widely used herbicide—in particular is a potent EDC.

Agent Orange-Contaminated Planes Could Have Sickened Vets After The War: Federal Report” is a 2015 Huffington Post article about US pilots who got sick from the dry residue of Agent Orange on the planes they had flown long after the Vietnam War ended.

Even though the U.S. Air Force and Department of Veteran Affairs long maintained that “dried residues” could not pose any health risk, the VA’s Institute of Medicine committee finally acknowledged that Agent Orange residue on C-123 cargo planes had likely caused illness in 1,500 to 2,100 Air Force Reserve personnel, who served aboard these planes long after the Vietnam War.


  • Glyphosate (Aquamaster/Roundup )
  • Triclopyr (Garlon 4 Ultra, Vastlan)
  • Imazapyr (Polaris, Stalker, Alligere Rotary 2 SL, Habitat,)
  • Aminopralid (Milestone)

In 2018, new herbicides were added to the list of permitted herbicides.

  • Glufosinate ammonium (Lifeline, Finale)
  • Imazamox (Clearcast)

Below is short list of what’s known about these chemicals.

Glyphosate (Roundup, Aquamaster): Probable Carcinogen

  • Probably causes cancer. According to the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) and the recent SF jury ruling.
  • Likely an endocrine disruptor.
  • Associated with birth defects. It’s been associated with birth-defects, especially around the head, brain and neural tube — defects like microcephaly (tiny head); microphthalmia (tiny undeveloped eyes); cyclocephaly (a single eye in the middle of the forehead).
  • Bad for the soil. It kills beneficial soil fungi but allows 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.
  • Bad for other living things. It’s very dangerous to frogs and other amphibians, and quite dangerous to fish.

Triclopyr (Garlon, Garlon 4 Ultra, Vastlan): Most Toxic of all?

Garlon, considered to be one of the most toxic of herbicides used in San Francisco and was listed as “HIGH PRIORITY TO FIND A REPLACEMENT” at least since 2009. The replacement, Vastlan, has the same active ingredient – triclopyr- and may well have the same issues (though the manufacturer says it’s safer.)

  • 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.
  • 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.
  • Garlon is also supposed to be twenty times as toxic to women as to men.
[the source – the Marin Municipal Water District; link to the PDF: ]

Imazapyr (Polaris, Stalker): The Chemical that goes On and On

  • Very persistent. In Sweden it was found in the soil 8 years after a single application. It not only doesn’t degrade, some plants excrete it through their roots so it travels through the environment.
  • 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 a neurotoxin, causing nerve lesions and symptoms similar to Huntington’s disease.” (The Journal of Pesticide Reform.)
  • It’s prohibited in the European Union countries, since 2002; and in Norway since December 2001 because of groundwater concerns.

From manufacturer’s label: “imazapyr should not be sprayed under trees you do not want to kill. This is a product that is mobile in the soil. It is capable of traveling from the roots of the plant on which it is sprayed into the roots of adjacent plants on which it has not been sprayed, killing or damaging plants that were not the intended targets of the spraying.”

SF Forest Alliance has a video of imazapyr being sprayed under the trees on Mt. Davidson.

Aminopyralid (Milestone): Persistent in Poop

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. The compost gets weed killer in it, and it doesn’t nourish the plants fertilized with the compost, it kills them.  See the 2009 article “Milestone Herbicide Creates Killer Compost” –

Dow AgroSciences stopped selling Milestone in the UK for a number of years. It was also banned in several places for fear of contamination.

Glufosinate ammonium (Lifeline, Finale): Neurotoxic

According to a 2007 monograph:

Carries unacceptable risks to humans, especially the neurological development of the foetus, to agricultural biodiversity, and to the environment. Chronic effects are primarily neurological and reproductive because glufosinate-ammonium is structurally similar to a neurotransmitter, glutamate, and interferes with its proper functioning:

Acute Toxicity effects are firstly gastrointestinal (nausea, vomiting, abdominal pain, diarrhea etc.) followed by the onset of neurological symptoms (convulsions and coma), then respiratory failure. Death results from circulatory failure. There’s no antidote.

  • serious effects on early embryonic development, including damage to the brain and neural tube.
  • causes the loss of many foetuses and damage to those actually born, including cleft lips.
  • transgenerational effects on brain function are reported.

Environmental Effects:

  • Moderately persistent in some soils, with potential to leach into groundwater, especially in sandy soils.
  • Insecticidal properties – toxic to beneficial organisms (spiders, predatory mites, butterflies).
  • Toxic to a number of soil micro-organisms, and may increase susceptibility to plants diseases, with consequent increased used of and dependence on pesticides.
  • Long-term use is likely to give rise to herbicide resistant weeds.

(Source:  Glufosinate-ammonium monograph, PAN, 2007)

Imazamox (Clearcast) was registered in 2010, information isn’t available. It’s being used in Golden Gate Park ponds and lakes.

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