Anchorage Daily News

Add knotweed to the ever-growing list of cars, trucks, stereos, Walkmans, CD players, flat-screen TVs, anime cheesy martial arts films imported from Japan. Unlike those entertaining and useful products, this deceptively appealing invasive plant has grown deep, strangling roots in Alaska gardens.

THE OFFENDER: Japanese knotweed, or Mexican bamboo (Polygonum cuspidatum), hails from the buckwheat family and thrives on long, sunny days, often reaching 10 feet in height. It's also rhizomatous, spreading through stout rhizomes and numerous reddish-brown, freely branched stems, and dioecious, producing male and female versions of the drooping, whitish flowers on separate plants. The oval leaves are 4 to 6 inches long, with an abrupt point.

The escaped ornamental thrives in disturbed areas, neglected gardens, roadsides and along stream banks. It's also edible from mid-April to early May, before the shoots grow tough and woody.

NOXIOUS NOTORIETY: This aggressive perennial forms dense stands that crowd out all other vegetation, degrading native plant and animal habitat. In addition, the plant creates a fire hazard in the dormant season.

The colonies rarely establish from seed, spreading mainly through plant fragments. Along streams, for example, plant parts fall into the water and infest new locations downstream. Long-standing rhizome clumps become woody with girths of a foot or more.

PREVENTING THE SPREAD: This adversary has established a fortress of deep-dense rhizomes, so plan a lengthy, multifaceted assault. Most folks start with digging and bagging the shoots, but regardless of precautions, some of the roots will snap off and new plants will sprout from the tiniest pieces left behind.

The same scenario goes for cutting back the vines throughout the summer. This approach stymies photosynthesis but, again, any shreds left behind quickly sprout new plants.

Because the first two tactics require a lot of work with limited results, most gardeners opt for weed killers that contain glyphosate, such as Gallup, Landmaster, Pondmaster, Ranger, Roundup, Rodeo and Touchdown. Though repeated spraying throughout the season hinders growth, the best time to apply the weed killer is late summer and early fall, when the plants are flowering and storing nutrients.

If all else fails, use plastic or poly tarps or carpet to cover and smother the stands.

MORE FLOWER FOR YOUR BOWER: As with any rhizomatous invader, the deep root system when removed leaves a big hole, so replant the area based on sunlight and moisture with such hardy perennials as lady's mantle, monkshood, columbine, English daisies, larkspur, lilies, lupine, blue poppy or phlox.

TRASH AND BURN: Serious muscle is required to pull this plant because of its deep, congested roots and dense ground cover. Double-bag and burn. Expect any slivers left behind to quickly sprout new plants.

BIG WILD WORRIES: For more information about Japanese knotweed or other noxious weeds, log onto the Integrated Pest Management program at www.uaf.edu/ces/ipm or www.uaf.edu/ces/cnipm, call 786-6300 to report a sighting, or drop off a sample at 2221 E. Northern Lights Blvd., Suite 118. Download a pocket Alaska weed guide at www.alaskainvasives.org.

J. Mark Dudick is a communications specialist at the UAF Cooperative Extension Service in Anchorage.

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