Eggleaf Spurge (Euphorbia oblongata)

It was introduced as a garden ornamental and escaped cultivation. It is toxic to some animals and reduces the livestock carrying capacity of pasture and range land by 20 to 50%.

Because of the large taproot, the plant must be dug. Mowing will only result in new shoots growing.

If sap contacts skin make sure to wash that area.

Butterfly Bush (Buddleja davidii)

It forms dense thickets that crowd out native plants and may alter soil nutrient concentrations. It’s difficult to control, can produce seeds during its first year and the seeds are viable for 3 to 5 years.

There are other bushes for the butterflies . . .

Giant Knotweed (Polygonum & Persicaria species)

Controlling invasive knotweed species typically takes a number of years and monitoring the site for regrowth is critical. 

Care must be taken not to produce new plants. All plant material should be removed and properly disposed of as new plants can sprout from very small fragments.

Himalayan Knotweed (Persicaria wallichii)

This grows vigorously into dense colonies that exclude native vegetation, alter natural ecosystems and are difficult to eradicate. It poses a significant threat to stream banks, where plants can survive severe floods. Small fragments can form new plants.

Japanese Knotweed (Fallopia japonica)

It is a very aggressive ornamental that is capable of forming dense stands, crowding out all other vegetation and degrading wildlife habitat.

It also creates a fire hazard in the dormant season. It is difficult to control once established.

Bohemian Knotweed (Fallopia bohemica)

An escaped ornamental, knotweed is often found in waste places, neglected gardens, roadsides, streambanks and riverbanks.

Invasive knotweed species look very similar. This one is a hybrid between Japanese knotweed and giant knotweed.

Scotch Broom (Cytisus scoparius)

It displaces native and beneficial plants, causing loss of grassland, ornamental perennials like rhodies, and even open wildlife-filled forest.

It aggressively spreads to unattended acreage to form monocultures, replacing desirable forage grasses and young trees visited by wildlife.

Seeds are toxic to livestock and horses.

You’ll find it surrounding most freeways in Western WA, where it was originally installed for winter erosion control. It’s done very well – so now cars just keep spreading the seeds to neighboring land.

Unfortunately, each seed can remain viable for over 30 years.

Yellow Archangel (Lamiastrum galebdolon)

This becomes very invasive and forms dense mats of groundcover vegetation which outcompetes native species and does not provide adequate food or cover for wildlife.

Some infestations in Washington are from abandoned hanging baskets that still had viable plants in them, which were dumped in natural areas.

Policeman’s Helmet (Impatiens glandulifera)

It is considered extremely invasive to moist, natural areas. Originally sold as ornamental, this species invades areas which include moist forests, stream sides and roadside thickets. Luckily, this plant pulls up easily, however the seeds have a 2 year viability – so follow-up control is a good idea.

Spurge Laurel (Daphne laureola)

This is a perennial shrub that has the ability to rapidly colonize areas forming monotypic stands and competing with native plants over a large area.

All parts of the plant are highly toxic.

Hand pulling (with gloves) small infestations is effective. Larger shrubs that are too big to pull can be cut below the soil line like blackberries. Keep an eye on the area for resprouts and then recut those as needed.

English Ivy (Hedera hibernica & Hedera helix) Ivy can outcompete native plants & limit the growth of understory plants. It kills understory and overstory trees by shading them out, plus it may cause storm damage to trees by acting as a sail.

The sap in the stems can cause skin irritation and rashes in sensitive individuals.

Consuming large amounts of leaves and fruits can be toxic to people and cattle.

Himalayan Blackberry (Rubus bifrons)

This species spreads aggressively and has severe negative impacts on native plants, wildlife and livestock.

There are a number of herbicide options for treating Himalayan blackberries, but cut them back to the ground first.

Fragrant Waterlily (Nymphaea odorata)

This can form dense stands in water that can cover hundreds of acres and can persist until the die-off in the fall. It can restrict lake-front access, eliminate swimming opportunities, and outcompete native aquatic vegetation.

Italian Arum (Arum italicum)

 This is a nonnative perennial that was originally introduced as an ornamental plant. It has now naturalized in a number of counties in Western Washington and appears to be spreading rapidly. It establishes in stream banks and similar habitats, and it’s very difficult to control once established.

Note: plant parts may cause skin irritation, which can be severe for sensitive individuals.

Old Man’s Beard (clematis vitalba)

Old man’s beard blankets the ground, shrubs and trees and can cause trees to collapse. It can rapidly grow along the ground in thick layers, blocking out light for other plants.

Seedlings can be hand pulled. Larger stems need to be cut and removed from the area.

Yellow Flag Iris (Iris pseudacorus)

This one is an invasive ornamental perennial that will sicken livestock if ingested.

When pulling it, care should be used to protect the skin as resins in the leaves and rhizomes can cause irritation. Also, all rhizome fragments must be carefully removed.

Pampas Grass (Cortaderia selloana)

This is a large perennial grass that grows in clumps with narrow leaves that grow to around 4 feet tall. Upright stems grow out of the tussock core, up to 6 -13 feet.

Cut and bag the stems prior to mechanical control to prevent spreading its seeds.

Pulling or hand-grubbing seedlings can provide effective control, but the entire crown and top root sections will need to be removed to prevent re-sprouting.