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Have you seen Fireweed (Senecio madagascariensis)?
Hawaii Early Detection Network Priority Pest for Kauai


fireweed flower
Fireweed flowers are about the size of a nickel and have exactly 13 petals.

Seedheads form into puffy, white, wind dispersed seeds.
Fireweed plant
Flowers occur at a loose cluster at the top of the plant. Grows up to 2 feet tall.
Images: Forest & Kim Starr and (inset far right) International Environmental Weed Foundation

Identification: Fireweed, aka Madagascar ragwort, is already widespread on the islands of Maui, Oahu, Lanai, and Hawaii, but can be prevented from invading Kauai. Fireweed is a daisy-like herb that grows up to 2 high. The stem is upright and slender with bright green leaves. The leaves are smooth, very narrow (only wide), have serrated edges, and they reach about 5 long. The small yellow flowers have 13 petals and are about the size of a nickel. The mature flowers turn into white thistle-like downy seed balls.
Impacts: Fireweed invades pastures, disturbed areas, and roadsides. It is very toxic to cattle, horses and other livestock. When ingested it causes illness, slow overall growth, liver-malfunction and even death in severe cases. In Australia, fireweed costs over $2 million per year in losses and control.
Dispersal Mechanism: Each plant can produce up to 30,000 seeds per year that are easily spread by wind, hiking boots, vehicles and animals. Fireweed is also spread unintentionally as a contaminant seed in hydro-mulch (the method of applying sprouted seeds in a slurry for rapid growth and erosion control) and on infested equipment.
Origin, Distribution, and Habitat: Fireweed is native to Madagascar and South Africa. Fireweed was first discovered on the Big Island in the 1900s and is now too widespread for control there. This pest can also be found on Maui and Lana'i. On Kaua'i, known infestations from hydro-mulched areas near Halfway Bridge and in Kalihiwai were controlled by KISC and HDOA. Kaua'i and O'ahu continue to be monitored for new infestation areas. The preferred habitat for this weed is disturbed grasslands, abandoned pastures and roadsides. Fireweed grows on a wide range of soils in sub-humid to humid subtropical woodland. Please let us know if you spot fireweed on Kaua'i!

More information about this pest external link


Fireweed look-alikes:


Bidens pilosa

Spanish needle flowers are small (0.1"-0.3" long and 0.05"-0.1" wide) and in dense clusters.

Spanish needle (Bidens pilosa):
Spanish needle is a widespread invasive herb on Kaua'i. It has tiny yellow flower clusters unlike fireweed's daisy-like flowers. Spanish needle also grows much taller; up to 6 feet.

THIS LOOK-ALIKE IS ALSO A PEST!

Bidens pilosa

The mature flowers turn into needle seeds unlike fireweed's white thistle flowers.

Wedelia (Sphagneticola trilobata):
Wedelia is another widespread invasive herb on Kaua'i commonly planted as an ornamental groundcover. It can be distinguished from fireweed by its larger yellow flowers which grow 1-2" wide. It also has a variable amount of pedals, unlike fireweed's constant 13.

THIS LOOK-ALIKE IS ALSO A PEST!

Sphagneticola trilobata
Last Updated: Monday January 30 2012. If you have any questions about the Hawaii Early Detection Network contact reportapest-maui@lists.hawaii.edu.
Funding and support for this project was made possible by the Hawai'i Invasive Species Council, the USDA Forest Service State and Private Forestry assistance, and University of Hawai'i-Pacific Cooperative Studies Unit.