Bay Leaf readers know we have many, many non-native plants in the East Bay. Some non-natives have become familiar and don’t cause much trouble, while others—the invasives—are a risk to the survival of our native plants and the integrity of our habitats.
By definition, invasives spread into otherwise undisturbed natural habitats, persisting and crowding out the native species. They lack natural enemies that could limit their spread and often have the characteristics of rapid reproduction, fast growth, wide dispersal, and tolerance of a wide range of environmental conditions. Unlike native species, which have co-evolved specific and sometimes intricate relationships with their pollinators, invasives attract only generalist pollinators. In addition, many invasives are unpalatable or even toxic to herbivores, so their value to the food web is low—and sometimes zero.
Many people are concerned about invasives and their control. The California Invasive Plant Council identifies them and tracks information about their spread; the U.S. Department of Agriculture investigates biocontrol options; the California Department of Food and Agriculture shares information about how to manage invasives; our local County Agricultural Commissioners’ offices designate noxious invasives and partner with land owners to control them. So if you are concerned about invasive plants, you are not alone!
Hand pulling works
I’ve been hand pulling the invasive, non-native stinkwort (Dittrichia graveolens) for about a decade. But how much difference can hand removal make in the management or control of an invasive species? On a small scale, plenty.
Last year was not the best year for the growth of stinkwort—other, earlier-developing species got a head start and perhaps outcompeted it. Still, at several of the sites we cleared in 2022—and I mean cleared carefully—we found no stinkwort in 2023. Zero. And at other sites, large ones, we found just a few small clusters of plants. This suggests that we missed just a few plants in 2022; we removed their progeny in 2023. In yet other sites, we have found a few scattered individual plants, suggesting that the seed bank is being depleted. This proves that removal and elimination is possible.
Better yet, we are seeing areas re-occupied by natives. Coast madia (Madia sativa) and willow herb (Epilobium brachycarpum) have moved into many places; skunkweed (Navarretia squarrosa) and centaury (Zeltnera sp.) into others. Surprisingly, I even found some places where blue-eyed grass (Sisyrinchium bellum) was making a comeback. These are places where the “seed rain” includes natives.
Naturally, non-native weeds also re-occupy areas where stinkwort is gone—typical replacements include bristly ox-tongue (Helminthotheca echioides) and pennyroyal (Mentha pulegium) in wet places; vetch (Vicia sp.), yellow star thistle (Centaurea solstitialis), and field hedge parsley, also known as sock destroyer (Torilis arvensis), in drier places.
Weeding invasives is its own reward, and…
Many Bay Leaf readers are weed-pullers, and almost all the rest of us appreciate why we do it. But what about the rest of the world? I pull stinkwort for the environment, and the satisfaction of a job done is reward enough. But something happened a few weeks ago, and I’d like to share it because it could apply to all of us.
I had just returned to my car after a stinkwort weeding session, hot and sweaty, and a nearby property owner popped out, wanting to talk about the weeds on his land. We exchanged information, and I gave him my stinkwort brochure. Then he gave me a level gaze and said, “I’ve seen you out weeding, and a lot of other people have too. You might not know this, but we really appreciate what you are doing.”
That made my day. Sometimes we wonder how we can spread the word about plants and the environment. This made me think; sometimes actions are just as effective as words. So to all of my silent weeding collaborators: your efforts may be valued more than you realize.
On balance, reducing the variety of invasives and increasing, at least to some extent, native plants, seems like a fair tradeoff for the work. Sustained, persistent, thorough effort will do it!
How you can help
If you are interested in removing weeds, and stinkwort in particular, you are welcome to join me. Or I can help to get you started on your own project, with tips, informational materials, and suggestions on how to get started. You can write to me at stinkwort@ebcnps.org.
And in the spirit of appreciation, I want to shout out thanks to Donita Hohenstein, who has spent hours working with me on stinkwort removal in the Lamorinda area.
—Barbara Leitner, Corresponding Secretary, CNPS East Bay Chapter, and stinkwort eradicator extraordinaire
March 2024
