Fireweed

fireweedFireweed, aka Madagascar ragwort
(Senecio madagascariensis)

(Asteraceae)

Considered very invasive and is on the Hawaii State Noxious Weed List.

Description:

  • Daisy-like herb that grows upright and branched, up to 50 cm (20 in) high.
  • Yellow flowers each have 13 petals and look like small daisies about the size of a nickel.
  • Flowers mature into white thistle balls
  • Native to Madagascar, introduction history in Hawaii unknown. Discovered in the early 1980s in pastures in Kohala on the Big Island, New populations introduced to Kauai and Oahu in contaminated hydromulch (groundcover seeds) from Australia, where it is also invasive

fireweed2Harm:

  • Each flower can produce 150 seeds, each plant can produce 30,000 seeds per year that spread by wind, hiking boots, vehicles or by animals when moved from infested to non-infested areas
  • Invades pastures, disturbed areas and roadsides
  • Toxic to livestock when eaten, it causes slow growth, illness, liver-malfunction and even death in severe cases.
  • One of the top 10 weeds of Western Australia where costs to the cattle industry and the Australian government exceed $2 million per year

In Hawaii:

  • Kauai: One known infestation from the hydromulched area near Halfway Bridge. KISC is assisting HDOA in controlling this population.
  • Oahu: Historically there have been several populations ranging from Kunia to Mana. All have since been removed and are monitored by HDOA, OISC, and Oahu Army Natural Resources Program.
  • Maui: Large infestations in pastures and along roadsides from Makawao to Ulupalakua.
  • Molokai: None known
  • Lanai: Known to be present, extent unknown.
  • Kahoolawe: Scattered individuals occasionally found on island. Nowhere common. Pulled and bagged when found.
  • Big Island: Infests many pastures from Parker Ranch in Hawi (Kohala) to Kahua Ranch. Found in Waimea toward Honokaa and Kona, and all the way in Kau. Too widespread for control. Landowners encouraged to control where possible.

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