The feel-good ending of the local news broadcast on Channel 7 (ABC) on February 17, 2021, featured this video of a huge field of oxalis (Bermuda buttercup, Oxalis pes-caprae) blooming on the roadside of Highway 1 in Santa Cruz County. People were stopping along the road to admire the bright yellow blooms of spring and photograph them. No one said anything about where the plant “belongs,” and no bad words were spoken about this useful plant that native plant advocates love to hate.
Despite its beauty and utility, oxalis is sprayed with one of the most toxic herbicides on the market in public parks and open spaces in the Bay Area. San Francisco’s Recreation and Parks Department has been spraying oxalis in several public parks for over 15 years. San Francisco Forest Alliance (SFFA) published a brilliant article about this pointless and destructive crusade that was republished by Conservation Sense and Nonsense in 2015. That article about the many benefits of oxalis is one of the most popular articles on this blog; it has been viewed by over 10,000 readers and many more on the SFFA website. We invite you to visit it and we summarize it briefly here:
Oxalis blooms briefly in early spring and dies back before summer begins, leaving the ground to other plants. It does not kill other plants, rather it co-exists briefly during its annual bloom.
Oxalis is very useful to pollinators and its tuberous roots (bulbils) are eaten by ground dwelling animals such as gophers.
Oxalis is called sour-grass because of its pleasant-tasting tang and it is often eaten by children.
Triclopyr is the active ingredient in the herbicide that is used on oxalis during its blooming season. It damages the soil by killing beneficial fungi and microbes, and it is toxic to many animals.
The annual poisoning of oxalis on Mount Davidson was recently videotaped by Ron Proctor and published by the San Francisco Forest Alliance. A crew of 5 men was hired to do the deed. Ironically, this spraying of oxalis on Mount Davidson in San Francisco was taking place at the same time that tourists were admiring oxalis in a neighboring county.
Oxalis is not an isolated example of a non-native plant that is admired by the public, but hated by native plant advocates and public land managers who do their bidding. As a member of the Sierra Club, I receive emails alerting me to opportunities to advocate for the protection of the environment. The most recent email featured a picture of a yellow wildflower in the foreground of a photograph of a Bay Area landscape:
The yellow wildflower in the foreground is Black Mustard (Brassica nigra). I responded to the Sierra Club’s email:
“The plant in the foreground of your photograph appears to be Brassica nigra: ‘Brassica nigra, or black mustard, is an annual plant cultivated for its black or dark brown seeds, which are commonly used as a spice. It is native to tropical regions of North Africa, temperate regions of Europe, and parts of Asia.’ Wikipedia
“I hope the use of this photo in this Sierra Club email to its members means that the Sierra Club is finally prepared to accept the reality of the presence of non-native plants in our public parks and open spaces. The Sierra Club’s support for unnecessary and destructive eradication projects has been regrettable, particularly because they require the use of harmful herbicides. I hope this email is an indication that the Sierra Club is finally ready to reconsider this futile crusade.”
I received this disappointing reply from the Sierra Club: “The staffer who puts together our newsletter isn’t a plant buff and wouldn’t have known the difference. But I am a plant buff and review the newsletter and know the difference between a mustard and a native plant. I somehow just overlooked that photo entirely. Thanks for bringing it to my attention. I’ll be more careful in my review of the newsletter in the future (look more carefully at the photos). And we’ll change the online version.”
The beauty and resilience of weeds
The Bottom Line
The general public doesn’t care where plants came from. The public recognizes and values beauty wherever it is found. Unfortunately, our public lands are in the death grip of the native plant movement and environmental organizations that should be objecting to the use of herbicides in our public parks and not promoting that destructive agenda. The crusade against non-native plants has been responsible for spraying our public lands with dangerous pesticides for over 20 years. They have little to show for their toxic crusade, perhaps because the herbicides damage the soil and make the survival of native plants even less likely.
The featured photo at the top of this article was taken in Glen Canyon, another public park in San Francisco where oxalis has been sprayed annually for many years. The copyright photo of a coyote in a field of oxalis was taken by Janet Kessler and is shown with her permission.
We briefly reactivate the Million Trees blog to publish an interesting and important debate between Jake Sigg and Professor Art Shapiro about the relationship between insects and native plants. Their debate was initiated by this statement published in Jake Sigg’s Nature News on April 26, 2019:
“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”
Jake Sigg has been the acknowledged leader of the native plant movement in the San Francisco Bay Area for 30 years. He is a retired gardener for the Recreation and Parks Department in San Francisco. Art Shapiro is Distinguished Professor of Ecology and Evolution at UC Davis. He has studied the butterflies of Central California for 50 years.
Jake and Art are both passionately committed to the preservation of nature, but their divergent viewpoints reflect their different experiences. Jake’s viewpoint is based on his personal interpretation of his observations. As a gardener, his top priority is the preservation of plants rather than the animals that need plants. As a scientist, Art’s viewpoint is based on empirical data, in particular, his records of plant and butterfly interactions over a period of 47 years as he walked his research transects about 250 days per year. The survival of butterflies is Art’s top priority.
Although their discussion is informative, it does not resolve the questions it raises because Jake and Art “agree to disagree.” Therefore, Million Trees will step into the vacuum their discussion creates to state definitively that it is patently false to say that “90% of insects can only eat native plants.” That statement grossly exaggerates the degree of specialization of insects and underestimates the speed of adaptation and evolution.
There are several reasons why insects do not benefit from the eradication of non-native plants:
Insects use both native and non-native plants.
Pesticides used to eradicate non-native plants are harmful to both plants and insects as well as the entire environment.
There is no evidence that insects are being harmed by the existence of non-native plants.
Insects use both native and non-native plants
This statement was recently made in an article published by Bay Nature magazine about Jake Sigg: “More than 90 percent of all insects sampled associate with just one or two plant families.” (7,500 insect species were sampled by the cited study. There are millions of insect species and their food preferences are largely unknown.) This exaggerated description of specialization of insects seems the likely origin of the subsequent, inappropriate extrapolation to the statement that specialized insects require native plants.
There are over 600 plant families and thousands of plant species within those families. Most plant families include both native and non-native plant species. An insect that uses one or two plant families, is therefore capable of using both native and non-native plant species.
We will use the Oxalidaceae plant family to illustrate that insects can and do use both native and non-native plants. Oxalidaceae is a small family of about 5 genera and 600 plant species. We choose that family as an example because Jake Sigg’s highest priority for eradication is a member of that plant family, Oxalis pes-caprae (Bermuda buttercup is the usual common name). In a recent Nature News (April 9, 2019), Jake explained why: “Oxalis is not just another weed; this bugger has a great impact on the present and it will determine the future of the landscapes it invades.”
Garlon is toxic to bees, birds, and fish. It is an endocrine-disrupter that poses reproductive and developmental risks to female applicators. It damages the soil by killing mycorrhizal fungi that are essential to plant health by facilitating the transfer of nutrients and moisture from the soil to plant roots.
A recent article in the quarterly newsletter of Beyond Pesticides explains that insecticides are not the only killers of insects: “Insecticides kill insects, often indiscriminately and with devastating consequences for biodiversity, ecosystem stability, and critical ecosystem services. Herbicides and chemical fertilizers extinguish invaluable habitat and forage critical to insect survival. Taken together, insecticides, fungicides, herbicides and chemical fertilizers make large and growing swaths of land unlivable for vast numbers of insect species and the plants and animals they sustain.” The loss of insects where herbicides are used to kill non-native plants are undoubtedly contributing to the failure of attempts to “restore” native plants which require pollinators and insect predator control as much as non-native plants.
In other words, eradicating non-native oxalis is damaging the environment and the animals that live in the environment. Furthermore, after twenty years of trying to eradicate it, Jake Sigg admits that there is more of it now than there was when this crusade began: “Maybe you’ve noticed that there’s more and more of it every year, and fewer and fewer other plants. That is unlikely to reverse.” (Nature News, April 9, 2019).
In fact, local failure of eradication efforts mirrors global failures of similar attempts: “…despite international policies aimed at mitigating biological invasions, the implementation of national- and regional-scale measures to prevent or control alien species has done little to slow the increase in extent of invasions and the magnitude of impacts.” (1)
Update:The California Invasive Plant Council has published “Land Manager’s Guide to Developing an Invasive Plant Management Plan.” It says very little about the disadvantages of using herbicides to eradicate plants they consider “invasive” other than a vague reference to “unintended consequences,” without discussion of what they are or how to avoid them.
However, it does give us another clue about why eradication efforts are often unsuccessful. When herbicides are used repeatedly, as they have been in the past 20 years, weeds develop resistance to them: “The International Survey of Herbicide Resistant Weeds (2018) reports there are currently 496 unique cases (species x site of action) of herbicide-resistant weeds globally, with 255 species…Further, weeds have evolved resistance to 23 of the 26 known herbicide sites of action and to 163 different herbicides.” The Guide therefore recommends that land managers rotate herbicides so that the “invasive” plants do not develop resistance to any particular herbicide. The Guide gives only generic advice to use “herbicide X” initially and “herbicide Y or Z” for subsequent applications.
In other words, the California Invasive Plant Council continues to promote the use of herbicides to kill plants they consider “invasive.” They give advice about ensuring the effectiveness of herbicides, but they do not give advice about how to avoid damaging the soil, killing insects, and harming the health of the public and the workers who apply the herbicides.
Do insects benefit from eradicating non-native plants?
There is no question that insects are essential members of every ecosystem. They are the primary food of birds and other members of wildland communities. They perform many vital functions in the environment, such as consuming much of our waste that would otherwise accumulate.
The Economist magazine has reported the considerable evidence of declining populations of insects in many places all over the world. (However, the Economist points out that the evidence does not include large regions where insect populations have not been studied. The Economist is therefore unwilling to conclude that the “insect apocalypse” is a global phenomenon.) The report includes the meta-analysis of 73 individual studies that describe declines of 50% and more over decades. The meta-analysis concluded that there are four primary reasons for those declines, in order of their importance: habitat loss, intensive farming, pesticide use, and spread of diseases and parasites. The existence of non-native plants is conspicuously absent from this list of threats to insect populations.
In other words, although the preservation of insects is extremely important, there is no evidence that the eradication of non-native plants would benefit insects. In fact, eradication efforts are detrimental to insects because of the toxic chemicals that are used and the loss of the food the plants are providing to insects.
Jake Sigg and Art Shapiro discuss insects and native plants
The discussion begins on April 26, 2019, with this statement published in Jake’s Nature News:
“Did you know that 90 percent of insects can only eat the native plant species with which they’ve co-evolved?”
On April 26, 2019, Arthur Shapiro wrote:
“No, I didn’t know 90% of insects can only eat the native plants with which they’ve co-evolved. I’ve only been studying insect-plant relationships and teaching about them for 50 years and that’s news to me, especially since on a global basis we don’t know what the vast majority of insects species eat, period! That’s even true for butterflies and moths, which are probably the best-studied group. And it’s even true here in California, one of the best-studied places on the planet (though way behind the U.K. and Japan). Where on earth did that bit of non-information come from?”
Jake Sigg responds:
“Art, I did my best to run down source for that statement. As I suspected, it may lack academic precision. That kind of precision is hard come by, and what exists is not entirely relevant. Most of the information comes from Doug Tallamy. But the statement is not accurate; it should have read “…90 percent of plant-eating insects eat only the native plants they evolved with”. Whether that is true or not I don’t know, but it accords with my understanding and I am willing to go along with it, even if proof is lacking. If you wait for scientific proof on everything you may wait a long time and lose a lot of biodiversity. I have had too much field experience to think that exotic plants can provide the sustenance that natives do.
I expect you will be unhappy with this response.”
On May 2, 2019, Art Shapiro replies:
“If Tallamy said “90% of the plant-eating insects that I have studied…” or “90% of the plant-eating insects that have been studied in Delaware…” or some such formulation I might take him more seriously. The phenomenon of “ecological fitting,” as described by Dan Janzen, is widespread if not ubiquitous. “Ecological fitting” occurs when two species with no history of coevolution or even sympatry (co-occurrence) are thrown together and “click.” A.J.Thorsteinson summed up some 60 years ago what is needed for an insect to switch onto a new host plant: the new plant must be nutritionally adequate, possess the requisite chemical signals to trigger egg-laying and feeding, not possess any repellents or antifeedants and not be toxic. That set of circumstances is met very frequently. To those of us who study it, it seems to happen every other Tuesday. As we showed, the urban-suburban California butterfly fauna is now overwhelmingly dependent on non-native plants. The weedy mallows (Malva) and annual vetches (Vicia) are fed upon by multiple native butterfly species and are overall the most important butterfly hosts in urban lowland California. . Within the past decade, our Variable Checkerspot has begun breeding spontaneously and successfully on Butterfly Bush (Buddleia davidii). The chemical bridge allowing this is iridoid glycosides. When I was still back East I published that the Wild Indigo Dusky Wing skipper, Erynnis baptisiae, had switched onto the naturalized European crown vetch (Coronilla varia) which had converted it from a scarce and local pine-barrens endemic to a widespread and common species breeding on freeway embankments. And the hitherto obscure skipper Poanes viator, the Broad-Winged Skipper, went from being a rare and local wetland species best collected from a boat to becoming the most abundant early-summer butterfly in the New York metropolitan area by switching from emergent aquatic grasses and sedges to the naturalized Mesopotamian strain of Common Reed, Phragmites australis. I can go on, and on, and on. If you find a sponsor for me to give a lecture about this in the Bay Area, I’ll gladly do it. If you promise to come!
I won’t snow you under with pdfs. Here’s just one, a serendipitous one that resulted from my walking near Ohlone Park in Berkeley. And one from the high Andes in Argentina. That paper cites one of mine in Spanish demonstrating that the southernmost butterfly fauna in the world, in Tierra del Fuego and on the mainland shore of the Straits of Magellan, is breeding successfully on exotic weeds.-! Copy on request.”
On May 2, 2019, Jake Sigg published his last reply:
“I believe many of your statements, Art, and many of these cases I am familiar with. A conspicuous local example is the native Anise Swallowtail butterfly that still lays eggs on native members of the Umbelliferae, the parsley family, but which also breeds on the exotic fennel, which is an extremely aggressive weed that in only a few years can transform a healthy and diverse grassland supporting much wildlife into a plant monoculture—that, btw, won’t even support the butterfly, which shuns laying eggs where its larval food plant is too numerous and easy target for a predator, like yellow jackets.
What puzzles me is why you can keep your equanimity at the prospect of losing acres of very diverse habitat to a monoculture of fennel. You live in the heart of the world’s breadbasket where for hundreds of miles both north and south there are almost no native plants except those planted by humans. That would tend to distort one’s view. I don’t mean to be flip, but it is not normal for even an academic to be indifferent about a loss of this magnitude. I have worked hands-on on the land (I was raised on a ranch) all my life and still work every Wednesday maintaining our natural habitat in San Francisco—a task that hundreds of citizens pitch in on because they value the quality and diversity of the areas. And why do you remain indifferent, are you just a contrarian? You cite examples to bolster your view, but the examples are too small a percentage to be meaningful and wouldn’t stand up against a representative presentation.
I got my view from life. I type this in my second-floor sunroom, which looks into a coast live oak growing from an acorn I planted in the late 1960s, about 50 years ago and which is immediately on the other side of the window. It is alive with birds of many different species—flocks of bushtits, chickadees, juncos every day (plus individuals of other species), which species-number balloons in the migratory season. What I can’t figure out is how the tree can be so productive as to stand up to this constant raiding. I will take instances of this sort as my guide rather than the product of academic lucubrations. And I will throw in Doug Tallamy; the world he portrays is one I recognize and love.
I think our battle lines are drawn. This discussion could go on, as we have not even scratched the surface of a deep and complex subject. But will either of us change our minds? No.”
“Jake Sigg: N.B. Art responded with another long epistle, not for posting. It clarified some of the points that were contentious and seemed to divide us. We differ, but not as much as would appear from the above discussion.”
(1) “A four-component classification of uncertainties in biological invasions: implications for management,” G. LATOMBE , S. CANAVAN, H. HIRSCH,1 C. HUI, S. KUMSCHICK,1,3 M. M. NSIKANI, L. J. POTGIETER, T. B. ROBINSON, W.-C. SAUL, S. C. TURNER, J. R. U. WILSON, F. A. YANNELLI, AND D. M. RICHARDSON, Ecosphere, April 2019.
The oxalis season is over, and the perky yellow flowers have vanished for another year. These Bermuda buttercups will be back next year to herald the spring, bringing joy to those who love them, irritation to those who hate them, and Tier I herbicides targeted at them in San Francisco’s so-called “Natural” Areas.
THOSE WHO HATE OXALIS AND WANT TO POISON IT WITH GARLON
These flowers are so visible in spring that Bay Nature magazine did an article about them in March 2015: A Natural History of the Little Yellow Flower that’s Everywhere Right Now. It quoted Jake Sigg, the retired SF Recreation and Parks gardener who is considered the doyen of San Francisco’s native plant movement. He hates oxalis pes caprae, which he considers extremely invasive. The article quotes him as saying that, without intervention, “in Xmany years Twin Peaks would just be one solid mass of yellow, and there wouldn’t be any other plants there…” The article suggested that an oxalis-dominated landscape “drives away coyotes, hawks and owls that feed on grassland foragers, and the situation is especially dire for endangered Mission blue butterflies, which depend heavily on native wildflowers.” Most of those ‘facts’ about oxalis are mistaken as we’ll explain below.
Mr Sigg’s theories align with those of the Natural Areas Program (NAP) of the San Francisco Recreation and Parks Department (SFRPD), which uses the herbicide, Garlon (triclopyr) to battle oxalis despite its dubious efficacy for the purpose. San Francisco’s Department of the Environment classifies Garlon 4 Ultra as Tier I: Most Hazardous. It’s listed as HIGH PRIORITY TO FIND AN ALTERNATIVE (their caps). Since oxalis is the main reason NAP uses Garlon, the alternative we propose is – don’t use Garlon or anything else on oxalis.
An article on SaveSutro.com, 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 female 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 is 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.
First, a little about the actual natural history of oxalis. This plant doesn’t set seed in California, and spreads entirely by sending out roots and forming little bulbils (like tiny potatoes) underground. It’s usually found where the soil has been disturbed by activities such as road-building, gardening, or trail-building. In some cases, the disturbance comes from landslides or something similar. It can’t stand frost. If we do nothing, it would tend to die down rather than spreading uncontrollably.
In disturbed landscapes, it can spread fast. For this reason it can be a nuisance in gardens. People don’t want to leave their gardens alone for years to let nature take its course with the oxalis, and not every garden design includes brilliant yellow as the dominant color for a few weeks. The only way to eradicate it in the short term is to dig it out carefully every time you see it, and make sure you get most of the bulbils. Or use strong herbicides, which may not work.
In a natural landscape, though, it’s a different story and here’s why.
1) OXALIS IS GOOD FOR BEES AND BUTTERFLIES
Oxalis is actually an excellent plant for bees and butterflies. When blooming, it provides “copious nectar.” In fact, it generously gives away its nectar. Since it doesn’t set seed, it doesn’t benefit from pollinators – but it’s a food source for honey bees, bumblebees and butterflies. (You can read a rather technical description of the plant HERE in a 2-page PDF note from UCLA’s Barry A. Prigge and Arthur C. Gibson.)
In fact, a recent 2014 study shows that plant communities with exotic plants had more plant species as well as more pollinators, that pollinators didn’t prefer native plants, and that even some specialist pollinators depended on introduced plant species.
It’s true the Mission Blue butterfly needs (native) lupine as its nursery plant. (It doesn’t depend on any other native wildflowers – only three varieties of lupine. Incidentally, one of the key nectar sources for the Mission Blue butterfly is an invasive non-native Italian thistle: Carduus pycnocephalus).
Lupine has been planted on Twin Peaks as NAP attempts to reintroduce the Mission Blue butterfly there. But lupine is also a plant of disturbed areas, which means that NAP must maintain it or it will die out as the area stabilizes. They have to keep planting it, weeding, and trimming the grass around the lupine patches to make it attractive to the butterfly. An SFRPD report on the reintroduction project said “unmanaged habitat deteriorates quickly.” Presumably, they don’t use Garlon near the lupine patches, since it would likely kill that too. Despite what is implied in the Bay Nature article, it’s not oxalis that’s the issue. The real problem is another native plant, the coyote bush which takes over grasslands in a natural succession.
2) OXALIS IS GOOD FOR WILDLIFE
Oxalis bulbils are a food source for wildlife. Gophers and other rodents eat them. In fact, the Bay Nature article says, “Their spread is abetted by pocket gophers and scrub jays, which have been spotted carrying the bulbs and caching them in the ground—effectively planting them in new areas.”
Since gophers are a foundation species in the food web, being dinner for predators from hawks to coyotes to great blue herons, these plants actually provide habitat benefits whether or not they’re flowering, because the bulbils are there all year.
Where there are gophers, the predators follow. Like the coyotes in these pictures, which clearly haven’t been driven away by a landscape dominated by oxalis.
3) OXALIS DOESN’T LEAVE THE GROUND BARE
The article says that oxalis leaves “bare ground during the six months of the year oxalis doesn’t flower.” That’s not true either.
The spectacular yellow bloom of the oxalis – valuable because the mass of color attracts honey bees and bumblebees – gives the impression that it’s the only plant there. But though it visually takes over the landscape when it’s in bloom, it naturally grows interspersed with grasses and other plants. Like in the picture above.
In fact, oxalis tends to enrich the soil with phosphorus, which is good for grass.
So when it finishes blooming, as it has by now – you don’t get bare ground. The picture below shows the same area as the first picture in this article – but it’s after the oxalis bloom is over. It’s grassland.
4) OXALIS HAS LITTLE IMPACT ON “NATIVE” PLANTS
One argument – related to the ‘bare ground’ argument – is that oxalis takes over grasslands and destroys them, particularly the native grasses. However, grasslands in most of California including San Francisco are dominated by 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 is primarily non-native anyway.
But anyway, what’s the evidence that oxalis is actually damaging native plants?
It’s true some European studies do suggest that an increase in oxalis is associated with a decrease in native plants diversity –though whether it’s a cause is unclear. It may just be benefiting from human activities that disrupt the landscape. Another study put oxalis head-to-head with a native annual grass, lolium rigidum. The native grass tended to dominate. Their conclusion: “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.
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
Children love oxalis, both for its pretty flower and for the sour taste of its edible stems.
Even small children love gathering posies of Bermuda buttercups (though picking flowers is technically prohibited in Natural Areas). The flowers are surprisingly hardy for wildflowers, and in a glass of water last quite well as cut-flowers.
The plant is edible, and its tart leaves make a nice addition to salad. People enjoy snacking on its sour stems. Besides Bermuda buttercup, it’s also called ‘sourgrass’ and ‘soursob.’ It does contain oxalic acid (as does spinach, for instance), and so you probably wouldn’t want to make a meal of it. Though in South Africa it’s made into soup.
Adding Garlon to it is probably a bad thing.
From our current evidence, 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.