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Invasive Weeds of Humboldt County the B-List: also of concern |
cotoneaster Cotoneaster franchetiiDescription: An attractive shrub used in landscaping, cotoneaster has pink to white flowers and bright orange to red berries. There are two species used commonly. The species that is known to have escaped into local forests is the one pictured, which has small clusters of berries and small leaves. The larger leaved species with large bunches of drooping berries, C. pannosa, has not yet been reported to escape. What it does: Cotoneaster has become naturalized in our local coastal forests. It is spreading rapidly and is expected to become a problem by displacing native shrubs. How to get rid of it: Remove this plant before the berries form. It resprouts from the base so grub out as much of the roots as possible. |
pittosporum (Victorian box)Pittosporum undulatum Description: This species of pittosporum is a popular landscaping tree in our area. It has attractive, wavy-margined, pale green, evergreen leaves. What it does: Unfortunately, this tree has escaped into local forests where it is spreading and threatening to become a major problem. The shrub species of this genus have not been reported to escape. How to get rid of it: You can chop this tree down, it is not known to resprout. Remove it be-fore it goes to fruit so you won’t spread any seeds. Contact the California Native Plant Soci-ety, 826-4801 for native alternatives to this species. |
English holly Ilex aquifoliumDescription: Another popular yard tree that is spreading into our local forests. These trees come in male and female form, and the berry-yielding females pose a greater threat, because birds spread the seeds. Holly has dark green, shiny, lobed leaves with spiny tips. What it does: Competes with native tree species. How to get rid of it: Remove it before berries form so you don’t spread the seed. Chop it down and grub out roots if possible as it may resprout. Watch for new seedlings from the seedbank. |
butterfly bush Buddleja davidiiDescription: Native to China, this attractive landscaping shrub has been spotted invading our local coastal forests. It has drooping cylindrical heads of purple flowers that resemble lilac, and narrow, pointed leaves. What it does: Butterfly bush is very aggressive, as you will know if you have tried to remove it from your yard or garden. It can out-compete native shrubs. How to get rid of it: You’ll need to be persistent as this shrub readily resprouts from the base. You can try grubbing out the roots, or after cutting it back cover it with black plastic for a winter. |
poison hemlock Conium maculatumDescription: A member of the carrot family, poison hemlock has characteristic “umbel”-shaped flowers, like Queen Anne’s lace. Poison hemlock can be distinguished from the common, benign members of this family by its height (up to 10 ft), and its characteristic red-spotted stems. What it does: Poison hemlock invades disturbed areas and riparian stream sides, where it crowds out native plants. It is extremely toxic to humans and livestock (this is the species that was reputedly used to poison Socrates). How to get rid of it: Be extremely careful when weeding out this plant as it can poison humans via ingestion of seeds. leaves, and roots and even as a result of blowing through the hollow stems. The seeds are the most toxic part of the plant. Using gloves, plants can be pulled up before fruiting (plants are annual so there is no need to pull up all of the roots). Repeated mowing close to the ground will also work. |
foxglove Digitalis purpureaDescription: It’s hard to miss this beautiful biennial wildflower, with its stalks of bell-shaped, purple flowers. It’s cultivated both for its beauty and as a medically important heart stimulant. What it does: This popular garden plant has escaped into the wild where it may grow so densely it crowds out native species. How to get rid of it: Pull it up before it goes to fruit. Wear gloves, as some people have reported numbness of the hands after handling this plant. |
parrot’s feather Myriophyllum aquaticumDescription: This species has been sold for use in aquariums, although its sale is now illegal in some states. It has a feathery foliage that can extend up to a foot above the water surface. What it does: Only female plants are present in our country so no seeds are produced, but plants spread aggressively vegetatively. Parrot’s feather forms dense mats of vegetation that can cover the surface of shallow lakes. Its tough stems then make it difficult to boat, swim, or fish. It provides ideal habitat for mosquito larvae. How to get rid of it: If you have this in your garden pond, remove it (but be sure you don’t dispose of it in any way that it can get into a natural water body). |
fennel Foeniculum vulgareDescription: A licorice or anise-scented perennial that sends up tall (10 ft) flowering stalks with bright yellow umbels of flowers. The leaves are feathery. What it does: This perennial, tap-rooted plant, introduced from Europe, escapes into natural areas and out-competes native plants. How to get rid of it: Cut it down before it goes to fruit and grub out the roots. |
teasel Dipsacus fullonumDescription: This is a familiar biennial plant of dried flower arrangements, and resembles a thistle. Teasel can be quite tall (over 6 ft) and has a spiny flower head with tiny purple flowers. Its leaves are opposite and stems are prickly. What it does: Native to Europe, teasel invades disturbed areas and is commonly seen along roadsides. Its presence can deter the return of native species. How to get rid of it: Before it fruits, pull it up using gloves to protect your hands from prickles. Or cut it down repeatedly until it dies. |
Klamath weed Hypericum perforatumDescription: This plant has bright yellow, five-petaled flowers with numerous showy, purple-tipped stamens The leaves are opposite. Purplish dots “perforate” the leaves and flowers. What it does: Klamath weed is a very aggressive plant that in-vades prairies, meadows, and pastures, where it outcompetes native plants. Grazing promotes this weed, which is poisonous to livestock. How to get rid of it: A successful biological control—a beetle—has been used to control this plant in northern California, and it is not nearly as prevalent as it once was. If you have it in your yard or field, call U.C. Cooperative Extension at 445-7351. |
periwinkle Vinca majorDescription: The bluish-purple, windmill-shaped flowers of this low-growing perennial ornamental are very distinctive. Leaves are shiny and opposite. What it does: This species has escaped into the wild where it forms dense mats that choke out native plants. How to get rid of it: If it occupies s a small area, cover it with black plastic for one or two seasons. You can also pull it up, but be sure to go back and check for resprouts. |
pennyroyal Mentha pulegiumDescription: Pennyroyal has relatively short flowering spikes (a foot or sometime taller) with bright lavender flowers arranged in circles around the stem. It has a strong peppermint scent. There are many different mints in our area, if you are unsure about the identity call the California Native Plant Society at 826-4801. What it does: Pennyroyal has invaded local wetlands and moist areas such as roadsides and ditches. It can form extremely dense mats that choke out native plants. How to get rid of it: Pennyroyal has rhizomes (underground stems) from which it will resprout. Your best bet is to cover it with black plastic until it completely dies. |
purple loosestrife Lythrum salicariaDescription: Purple loosestrife is a showy perennial from Europe with beautiful purple flowering spikes. It is from 1.5 to 8 ft. tall Its four-sided stems can be smooth to hairy. Leaves are four inches long, lance-shaped, and whorled. What it does: This plant has choked freshwater wetlands across the United States, earning it the nickname “the purple plague.” It has only recently been spotted in Humboldt County, so be especially vigilant and avoid planting this in your garden. How to get rid of it: Since this plant is so difficult to control once established, your best defense is to detect it early and prevent its spread. If you see this plant, contact U.C. Cooperative Extension at 445-7351. |
evening primrose Oenothera glaziovianaDescription: This is a popular biennial garden plant with large showy yellow flowers (with four petals) borne on leafy spikes. What it does: This species of primrose is probably a hybrid de-rived in Europe from two North American species. It readily hybridizes with two of our native evening primroses, Oenothera elata and the rare Oenothera wolfii . This interbreeding is a threat to the native species. How to get rid of it: It can be difficult to tell the natives from the introduced species if you are not familiar, so ask for help from the California Native Plant Society if you are not sure (826-4801). The native O. elata has flat leaves, while the introduced species’ leaves are crin-kled. O. wolfii has smaller flowers (petals less than 1 inch) Pull up the introduced species be-fore fruiting, or repeatedly mow it. |
birdsfoot trefoil Lotus corniculatusDescription: Bright yellow pea-shaped flowers grow in low mounds. Plants have 3 leaflets. What it does: Takes over disturbed areas, pastures, and wetlands. How to get rid of it: This plant spreads by a prolific seed bank as well as vegetatively. The best strategy is to get rid of it right away before a seed bank forms. You’ll need to grub out the roots, and it may take several years of checking for resprouts. |
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