Problem Aquatic and Terrestrial Plants

Most of the problem aquatic and terrestrial plants in Western Washington are not native to this area, having been introduced to our region through human activities. Due to their aggressive growth patterns and a lack of natural enemies here, they spread rapidly into native plant communities. This reduces habitat diversity, food and shelter for many wildlife species, and the ability of the natural environment to perform a wide variety of important ecological functions.

Because of these habits, problem aquatic and terrestrial plants are often referred to as invasive non-native plants or invasive weeds. This appendix provides descriptions of some of the most invasive aquatic and terrestrial plants which can impact natural habitats, with specific information on the impact of the plant and methods for controlling it.

1. Preparations and Planning
Before trying to control invasive non-native plants, make sure you have correctly identified them. (Your local conservation district or weed control board can often help with this.) In certain situations you may need to get permits (for example, to work in or next to a stream or lake, or to burn plant material): consult local land use departments for guidance. If you wish to remove the plants from public or vacant land, you will also need to get the property owner's permission.

Plan for on-going maintenance to ensure your efforts are not wasted. In addition, plan on replacing invasive non-natives with native plants to prevent reinvasion by the same or another non-native.

2. Removing and Disposing of Invasive Non-native Plants
Many control methods are available, including hand removal, herbicides, and biological controls. Care should be taken to choose a strategy that causes the least environmental harm while still being effective. Controlling invasive weeds without negatively impacting water quality or spreading the weed is sometimes difficult.

As much as possible avoid disturbing the soil, since disturbed soils are ideal sites for the seeds of invasive non-native plants to germinate. Often the best control method is to remove only part of the plant, such as seed heads or the above-ground portion. Avoid leaving any fragments which might re-sprout, and take particular precautions to not spread the seeds if the plant is in seed. Also be careful not to disturb wildlife: if birds or other wildlife might be nesting, reschedule your removal efforts.

Dispose of invasive weed materials in a manner that will prevent further infestation. All species except Scot broom should be removed from the site or burned to prevent re-sprouting. Purple loosestrife, in particular, should be bagged securely in plastic and hauled to a landfill. (Some counties may pay dump fees for invasive weed material– check with your local weed board or conservation district). Other weeds, such as invasive blackberries, may be shredded and composted.

3. Replanting with Native Plants
Replant disturbed areas with appropriate native plants to prevent re-growth of the invasive weeds. Emergents such as bulrushes are effective in wetter soils. Shrubs such as salmonberry or red-osier dogwood, or trees such as black cottonwood, western red cedar, or willows work well in areas infested with reed-canary grass or invasive blackberries. Avoid highly aggressive plants such as cattail or spirea, so you don't replace a problem non-native with a problem native plant.

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