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Invasive Weeds of Humboldt County the A-List: the most harmful |
Scotch broom Cytisus scopariusDescription: This yellow-flowered shrub of the pea family is native to southern Europe and northern Africa. It has large, yellow, pea-shaped flowers, small leaves, and rigid stems. There are several other brooms that are similar in appearance, although some have orange-yellow flowers, and all are invasive. What it does: Scotch broom is aggressive and crowds out native plants. It adds nitrogen to the soil, causing changes that may be detrimental to native plants. How to get rid of it: If possible, use a “weed wrench” or a tool that can remove the plant by the roots. If you chop down large plants you will need to grub out roots or they will resprout. Continue to treat the area because new plants may sprout from the seedbank. Remove this plant before flowers produce seed pods so you don’t spread the seeds. |
pampas grass Cortaderia jubata Cortaderia selloanaDescription: Pampas grass, native to South America, is an attrac-tive, tall grass often used in ornamental gardening. Its flowering plumes are often silvery in appearance. What it does: Pampas grass crowds out native species. It pro-duces millions of wind-borne seeds asexually. How to get rid of it: Control this plant BEFORE it sets seed, if flowering plumes are present remove and bag them carefully in a sealed plastic bag before disposing. Stems can be chopped down with a pulaski or axe, then dig out the root ball and remove it, using a combination of chopping and digging. If you can’t get the rootball out, chop it and cover with black plastic for 6 months. additional information at WRIC |
gorse Ulex europaeaDescription: This shrub from Europe has yellow and orange pea -shaped flowers similar to Scotch broom, but can be easily distinguished by its vicious spines. What it does: Gorse aggressively displaces native species. It is relatively uncommon in Humboldt County, so report any new occurrences to UC Cooperative Extension, 443-7351. How to get rid of it: Preferably, remove this plant by the roots with a tool like a weed wrench, or it will resprout. Remove it before the flowers turn to pods. |
Himalaya berry Rubus discolorDescription: You can distinguish this Eurasian shrub from its native relative by the number of leaflets (five on Himalaya berry, three on Pacific blackberry) and its courser arching stems. What it does: Despite its tasty berries, this shrub poses a threat by creating dense thickets that shade out native plants. How to get rid of it: Good old fashioned grubbing is the way to rid yourself of this tenacious shrub. It will resprout from remaining roots and sprout from seed, so go back and pull new starts annually. Goats will eat this plant, but be sure not to spread seed in this way. |
English ivy Hedera helixDescription: Most people recognize this common ground cover. It has waxy leaves that assume a more rounded shape when it climbs up trees. Only the aerial plants produce fruits. What it does: English ivy smothers other ground-covers, shrubs, and the tallest trees. It may take awhile, but this popular ivy will kill your spruce and redwoods, so act now. How to get rid of it: The most important place to start is on plants that have begun to climb. These “aerial” plants will produce fruits that can be dispersed by birds. These are the easiest to kill, simply “girdle” the tree, cutting through the stems of ivy (but be careful not to harm the tree). Plants that aren’t fruiting will spread along the ground. You’ll need to pull it up repeatedly, getting as much of the root as possible. Eventually it will die, but be persistent and watch for seedlings that come up from the seed bank. |
Cape ivy Delairia odorata also known as German ivy
Description: Although it’s not a true ivy, Cape ivy is named for its ivy-like, waxy leaves, which have sharper points than English ivy. What it does: Cape ivy blankets and smothers native plants. How to get rid of it: Keep cutting it back and pulling it up. It’s tough to get rid of! |
European beachgrass Ammophila arenariaDescription: European beachgrass is a tough, perennial grass found on dunes. It has narrow, rolled, green leaves, turning brown in fall; compared with the broad, flat, blue-green leaves of native dune grass (Leymus mollis). What it does: This aggressive grass is responsible for nearly wiping out native foredune communities along the west coast. It creates a steepened foredune and cuts off sand flow, starving the native dune plants that need moving sand to thrive. How to get rid of it: You’ll need to dig out the grass to a depth of your shovel blade, preferably in spring. Then return every few weeks to dig up new resprouts. If you do this diligently the grass will die in one to two seasons. Burn the piles after they dry. |
iceplant Carpobrotus edulisDescription: Iceplant is found on our dunes and beaches. It has very succulent leaves and bright purple or yellow flowers. It is named for its fig-like fruit. What it does: Iceplant forms dense patches that grow right over native plants. It raises the salinity of the soil, making it less suitable for native plants. Seeds are eaten by rabbits, which improves germination. How to get rid of it: If you have a dense patch, have a group of people help you “roll it up” like a carpet, as you sever the roots underneath. Looser patches need to be dug up. Iceplant regrows from underground stems so you’ll need to repeat your treatment for several seasons. |
yellow bush lupine Lupinus arboreusDescription: The yellow, pea flowers of this woody shrub bloom around June. It is the only shrubby yellow lupine in our area, and is found on dunes. What it does: Yellow bush lupine overstabilizes dunes, starving the native plants of needed sand movement. It nitrifies the soil which prevents natives from returning. Seeds in the ground can last decades. How to get rid of it: Chop it down before it flowers, and especially before it fruits. Small seedlings can be pulled up. Normally shrubs will not resprout from stumps. The seedbank lasts for years so you’ll need to keep pulling up resprouts if the plants have been there awhile. Compost (if no seeds present) or burn the remains. |
yellow star thistle Centaurea solstitialisDescription: Yellow star thistle is a very prickly plant, up to 3’ tall, which starts as a basal rosette of deeply-lobed, white-woolly leaves. The flowers (solitary at the end of branches) have outward pointing, stiff, inch-long spines. What it does: Introduced from the Mediterranean region, this plant takes over rangelands, roadsides, pastures, and fields. It has negative impacts on recreation, livestock grazing, and wildlife values. It is poisonous to horses. How to get rid of it: If you have this plant on your land, contact your County agricultural representative (445-7223) to report its presence, for tips on its eradication, and to prevent its spread. additional information at California Wild |
spotted knapweed Centaurea maculosa (above)diffuse knapweed C. diffusa (below) Description: Spotted knapweed grows up to 4’ tall. Leaves are pinnately divided, flowers are pink to purple. A distinguishing feature is the black tip on the bracts of bud. Diffuse knap-weed produces a much-branched stem up to 2’ tall. Flowers are mostly white, sometime purple. The bracts surrounding each flower have 4 to 5 pairs of horizontal spines and one long vertical spine—spotted knapweed does not have this vertical spine. 
What it does: Introduced from Eurasia, these species are among the greatest weed threats
in the Western U.S. Their presence in rangelands severely decreases the feeding value to
livestock and wildlife.How to get rid of it: Like yellow star thistle, control methods are complex. Some biological controls are available. Contact U.C. Cooperative Extension at 445-7351). |
bull thistle Cirsium vulgare (above)Canada thistle C. arvense (below) Description: Bull thistle has larger, more magenta flowers, while Canada thistle has smaller, lavendar flowers. Both are found on roadsides, pastures, and vacant lots. The Canada thistle has both male and female plants, the female flowers (shown) are showier than the males. 
What it does: Crowds out native plants, discourages grazing in pastures.How to get rid of it: After plants bolt but before the flowers go to fruit, cut or pull up plants (since they are biennial they will die after flowering). Use gloves. June-July is a good time. |
common reed Phragmites australisDescription: This is a very tall grass, taller than a person, and grows in dense stands in wetlands. It flowers late in the summer. What it does: Common reed grows in very dense patches, where it shades out native wetland species in both brackish and salt marshes. How to get rid of it: Common reed is not yet widespread in Humboldt County, known only from a few locations in and near Eureka. If you find it elsewhere, contact UC Cooperative Extension at 445-7351 to report the occurrence and for information on control. |
Spanish heath Erica lusitanicaDescription: This shrub, erroneously called heather, is popular in florists’ bouquets. It has beautiful tiny, white, bell-shaped flowers and needle-like, evergreen foliage. What it does: You can see this plant along Highway 101 south of Eureka and near Trinidad. It alters soil pH making it hard for native plants to survive. How to get rid of it: Chop it down, grub up roots as they resprout. Be persistent because there is a seed bank. Pile and burn remains when dry. |
Chilean cordgrass Spartina densifloraDescription: This perennial grass is found only in salt marshes. Historically, Humboldt Bay’s salt marshes had no cordgrass, although there is a native cordgrass in San Francisco Bay. The species in Humboldt Bay was introduced from Chile. It can form discrete tussocks or look like a homogeneous pasture of grasses. It flowers during the summer months, and is the only tall (2 ft. or higher) grass you will see in the salt marshes. What it does: Chilean cordgrass now blankets the vast majority of our salt marshes. It out-competes native plants, including our rare salt marsh species. How to get rid of it: This species spreads both vegetatively and by seed, and is so widespread that successful control on a large scale will probably require a biological control. To show your concern, write your legislators and urge research on control methods. |
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