To Every Weed There Is a Season


Lisa Bryan, KP News

The bright yellow flowers of tansy ragwort (Senecio jocobaea) make it easy to spot throughout July and into August. Photo: Lisa Bryan, KP News

Tansy ragwort is one of seven invasive weeds that the Pierce County Noxious Weed Control Board (PCNWCB) targets for control. Poisonous to livestock and humans, each mature plant produces upward of 150,000 seeds. August is prime time for spotting it and preventing its spread.

Plant recognition is the first step. Mature plants grow from 3 to 6 feet tall with bright yellow clusters comprised of small daisy-like flowers, each with 13 petals. Once familiar, the plants are easily identified from a distance. Prevention of further seed production is the next step toward controlling their harmful spread.

During the July 12 meeting of the Key Peninsula Community Council, Education Representative Morgan Heileson of the PCNWCB presented “The Sinister Seven,” a list of noxious weeds requiring mandatory control measures within Pierce County, including poison hemlock, spotted knapweed, gorse, wild chervil, dalmation toadflax, tansy ragwort and giant hogweed.

Washington state classifies noxious weeds into three groups. Class A mandates eradication statewide. Class B requires control as applicable countywide. Class C includes invasive species where control is strongly suggested.

Violation notices are mailed to property owners where noxious weeds have been observed by a licensed weed inspector. Once notified, property owners are required to promptly remove and properly dispose of noxious weeds or risk fines. Inspectors monitor the site for compliance within the specified time period and continue to monitor infestation sites in the future.

Giant hogweed

As early as 1881, the legislators of Washington Territory outlawed the growing of Canada thistle, accidentally introduced by seed to North America in the1600s. The misdemeanor offense carried a stiff fine of $10 for any landowner caught with the plant on their property. By 1964, RCW 17.10 established the Washington State Noxious Weed Control Board.

The term “noxious weed” is the legal phrase for highly invasive nonnative plants whose continued proliferation threatens lasting environmental and economic damage. The presence of noxious weeds negatively impacts agricultural production, proper soil drainage, increases the risk of erosion, flooding and wildfire. Accidental ingestion of certain noxious weeds is highly poisonous, producing toxins potentially deadly to livestock and humans.

“We’re available for on-site consultations to assist property owners with identification, effective control techniques and proper disposal methods to bring problem infestations under control,” said Heileson. She advised an abundance of caution when handling and working with noxious weeds.

Giant hogweed is a dinosaur of a plant towering 15 to 20 feet in height with white umbrella-like blossoms measuring 2-1/2 feet wide. This poisonous Class A Noxious Weed requires eradication statewide. The 2 to 4 inch thick stems contain a toxic sap that causes severe burns and scarring that may last for many years. May is the ideal month to look out for it.

Poison hemlock

“The watery sap of giant hogweed can squirt out 5 feet from the plant once cut or punctured,” Heileson said. “A single drop of toxic sap in your eyes can cause permanent blindness. If you do come into contact with sap, wash the affected area with soap and water. Stay out of the sun for at least 48 hours to minimize scarring.”

All parts of poison hemlock are acutely toxic to humans and animals; even the dead, hollow canes remain toxic for three years. The plant grows 4 to 6 feet tall with leaves resembling parsley or carrot tops. Poison hemlock is identifiable by its smooth stems with purple blotches. Washington Poison Control receives over 40 exposure reports annually. Gloves and protective clothing must be worn when handling poison hemlock and facemasks are advised to avoid breathing the pollen. March is the best month to locate poison hemlock and control new plants.

KP Councilmember Don Swenson said he was impressed after attending a similar PCNWCB presentation last spring. “It’s really amazing what you see out there once you start looking,” he said.

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