This would be the earliest documented record of this species in Washington. Growth, Development, and Reproduction Giant hogweed is a perennial which takes several years from germination to produce the first flowering stalk. It is believed to be monocarpic, dying after first flowering and seed set. Individual plants however, may produce additional crowns which continue to flower and set seed. Seed longevity is known to be greater than seven years.
Reproduction is through seed and perennating buds formed on the crown and tuberous root stalk.
Abundant seed production, a persistent root stalk, and vegetative reproduction from perennating buds are cited as reasons for its capability to colonize rapidly and expand populations. Response to Herbicides 2,4-D, TBA, MCPA and dicamba will kill above ground parts but are reportedly not particularly effective on persistent rootstalks. Glyphosate is considered the most effective herbicide and should be used cautiously around desirable species since it is nonselective. Application during bud stage and while the plant is actively growing is recommended by New York Cooperative Extension. In wet areas Rodeo is the only herbicide permitted for use in Washington.