Knotweeds: Japanese Knotweed (Polygonum cuspidatum), Bohemian Knotweed (Polygonum x bohemica) (Fallopia X bohemicum), and (Japanese x Giant) Hybrid Knotweeds
Buckwheat family

Plant Identification: An herbaceous perennial that forms extremely dense stands, shading out native vegetation. Stems to 10 feet tall, hollow, bamboo-like with thickened nodes where the leaf stalks meet the stem. Reproduces from extensive spreading rhizomes or broken-off pieces of stem. Leaves broadly oval and up to 6 inches long. Has small white to greenish-white flowers that bloom in late August/September. Dies back, turning bright yellow before dropping leaves in the fall.

Threat: Clogs waterways and lowers quality of habitat for wildlife, fish, and invertebrates. Has displaced salmonberries along shorelines.

Found: Currently spreading in Juneau and Metlakatla. Also found in small patches in Cordova, Haines, Angoon, Sitka, Kodiak, and other Southeast Alaska communities. Found on roadsides, stream banks, and beach meadows.

Distribution Map:Japanese Knotweed (Fallopia japonica, Polygonum Cuspidatum, and hybrids) (External Link to EDDMapS website)

Detailed information sheet (Link to .pdf at UAA ENRI Alaska Natural Heritage Program)

Knotweed Control: Here are some hints to controlling knotweed mechanically (without herbicides).

1. Follow the Four T’s- Timely, Tenacious, Tough, and Thorough: Visit site a minimum of 8 times in a season.
2. Start early, and cut all new growth every couple of weeks during its growing season which reduces plant mass and disposal needs. (Growth in 2010 was incredibly rapid in the first three weeks of May from ½ in. sprouts to 5 feet.)
3. Work around the infestations perimeter, toward the center.
4. Realize knotweed reacts to cutting, chopping, and tilling by spreading (initially).
5. Mark the farthest shoots of your infestation with every cut chop or stomp.
6. Be very careful when disposing root material: It only takes ½ inch of root to grow a new plant and can travel in water.
7. Extend coving material several feet beyond the farthest sprout, use the heavy felted material when possible.
8. Monitor for several years (3-7).
9. Plan for re-vegetation and remove non-organic materials (landscaping material, etc.)

Additional Knotweed Control Information:

Basic Knotweed Information and Control (.pdf, 557 kb)
Comparative Herbicide Options for Knotweed Control (.pdf, 735 kb)
Control Options for Invasive Knotweeds (.pdf, 416 kb)
A Homeowner's Guide to Controlling Invasive Knotweeds (.pdf, 1357 kb)

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