Invasive Species

Invasive plants are a big problem in Arcata. They harm the look and function of our landscapes, recreation areas and waterways. Please help the City to control them and protect our natural environment. Know what they look like and do your best to control them at home. Help protect our open spaces by joining an invasive plant removal workday or organizing your own! 

Learn more about local invasive plants!

The plant species pictured below are 'Red Alert' species, meaning they are relative newcomers with limited distribution. Quick response is the most cost-effective way to control their spread. If you see any of these invasive species, please call the Humboldt County Department of Agriculture at 707-441-5260 or email to report your sighting. The City of Arcata is also a partner in the Humboldt Weed Management Area. More information can be found here!

Red Alert Species

Keep an eye out for these 8 invasive plants! 

Gorse (Ulex europaeus)


Tree-of-Heaven (Ailanthus altissima)


Shiny Geranium (Geranium lucidum)

Shiny Geranium

Purple Loosestrife (Lythrum salicaria)

Purple Loosestrife

Japanese Knotweed (Reynoutria japonica)

Japanese Knotweed

Spotted Knapweed (Centaurea stoebe ssp)

Spotted Knapweed

Diffuse Knapweed (Centaurea diffusa)

Diffuse Knapweed

Himalayan Knotweed (Persicaria wallichii)

Himalayan Knotweed

Report your sighting to the Humboldt County Department of Agriculture: