Garlon is one of the two pesticides that UCSF proposed to use to prevent re-sprouting of felled eucalyptus, blackberry and vines. It is regularly used on Twin Peaks, one of the highest points in the city.

We should mention that on Mount Sutro, UCSF is currently using  no herbicides at all. Neither is the Marin Municipal Water District, and it’s easy to understand why. Someone sent me the chapter on Garlon from the Marin Municipal Water District (MMWD) draft Vegetation Management Plan. (You can read that here:Chap4_Triclopyr_8_27_08 ) 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.

[Edited to add: Garlon is also used by the East Bay Regional Parks District.]

Garlon, the herbicide called triclopyr, kills broad-leaved plants (not grasses or conifers) by sending them a hormonal signal to grow uncontrollably. This weakens the plant until it dies. Its breakdown products are triclopyr acid and then ‘TCP’ – both of which are, fortunately, somewhat less toxic than Garlon. (Imazapyr,  by contrast, breaks down into a neurotoxin.)

THE DANGERS OF GARLON

Garlon 4

What stood out, though, was how much is not known, particularly about the effects of repeated low-level exposure. There simply isn’t that much research out there, and few human studies. “Although triclopyr has been registered in the US since 1979, there are still very few studies on triclopyr that are not part of the EPA registration process.” Most of the research that exists is on Garlon 4. What is used on Twin Peaks is Garlon 4 Ultra. It’s similar but isn’t mixed in kerosine. It’s mixed in a less flammable but apparently equally toxic methylated seed oil.

What is known makes uncomfortable reading.

• Garlon “causes severe birth defects in rats at relatively low levels of exposure.” The rats were born with brains outside their skulls, or without eyelids. “Maternal toxicity was high” and exposed rats also had more failed pregnancies.

• Rat and dog studies showed damage to the kidneys, the liver, and the blood. It’s insidious, because there’s no immediate effect that’s apparent. If someone’s being poisoned, they wouldn’t even know it. In a study on six Shetland ponies, high doses killed two ponies in a week, and two others were destroyed.

• About 1-2% of Garlon falling on human skin is absorbed within a day. For rodents, its absorbed twelve times as fast. Too bad for the gophers…

• It isn’t considered a carcinogen under today’s more lenient guidelines, but would have been one under the stricter 1986 guidelines.

• Dogs may be particularly vulnerable; their kidneys may not be able to handle Garlon as well as rats or humans. “The pharmacokinetics of triclopyr is very different in the dog, which is unique in its limited capacity to clear weak acids from the blood and excrete them in the urine.” Dow Chemical objected when EPA said that decreased red-dye excretion was an adverse effect, so now it’s just listed as an “effect.”

• There was insufficient information about Garlon’s potential effect on the immune system, or as an endocrine disruptor.

• It very probably alters soil biology. “There is little information on the toxicity of triclopyr to terrestrial microorganisms. Garlon 4 can inhibit growth in the mycorrhizal fungi…” (These are  funguses in the soil that help plant nutrition.) No one knows what it does to soil microbes, because it hasn’t been studied.

• It’s particularly dangerous to aquatic creatures: fish (particularly salmon); invertebrates; and aquatic plants.

• It doesn’t [ETA: generally] kill adult honeybees, but there are no studies of other insects. [ETA: Some studies show slight “acute toxicity” to honeybees.]

• Garlon can persist in dead vegetation for up to two years.

Given all the information we do have on this chemical (and all the information we don’t have ) we have to question why native plant restoration is worth spraying poisons on some of the highest points in our city. Garlon must be used when the weather is wet; if the plants don’t have water, they will not grow and the chemical won’t work. But the runoff from these hills is enormous during the rain – it washes down in rivulets and streams, and it will end in the reservoirs, the groundwater, and the bay. Garlon notices were up on Twin Peaks for most of March 2010.

FUTILE POISON?

We also question whether it even achieves the the nativists’ objective. On Twin Peaks, it’s targeted at oxalis, but Garlon is not a precision instrument. It will kill all broadleafed plants, native or otherwise, and favor grasses. Over time, Garlon use will convert Twin Peaks to non-native grasses (because those grow faster than native ones).

Slightly ironic

We can only speculate what it does to resident insect populations, because there’s no data. No ant studies. No caterpillar studies. No Mission Blue Butterfly studies, despite its use in a Mission Blue Butterfly area. The only studies show that adult honeybees aren’t being immediately killed. Long-term hive studies? None of those, either.

Meanwhile, the soil chemistry is probably being altered, and a regular dose of toxins added to our watershed in our “Native areas.” We have no idea whether there’s a particular risk to dogs being walked in Garlon-sprayed areas, or to pregnant women there or in the homes below the Garlon-sprayed hills. Based on the current levels of research and information, we’d guess that San Francisco’s Recs and Parks has no idea either.