top of page

Devil Weed

Updated: Sep 16, 2020

An aerial spraying project by the Army to control one of the world’s worst 100 invasive species, Devil Weed, was put on hold until further notice, due to community concerns.

The Army was planning to use a small utility helicopter equipped with an extendable boom and spray nozzle covered by cowling to target Devil Weed growing on the cliffs and rough terrain of Kaunala Valley, near the motocross track. The proposed herbicide was Ranger Pro, which contains glyphosate.

Community opposition grew rapidly through social media when someone posted that widespread aerial spraying of 900 acres was to occur. Of course, this description conjures up images of blanket crop dusting, which was never the plan. The Army agreed to pause and re-evaluate its options to control this invasive plant which is a threat to several endangered species in the area.

Devil Weed (Chromolaena Odorata), aka Siam weed and bitter bush, is a highly invasive pest and rates extremely high on the Hawaii Weed Risk Assessment. It has the potential to become exceedingly invasive and detrimental to our native ecosystem if not contained and eradicated. First detected in the Kahuku Training Area in 2011, it has been found in Pupukea, Aiea and Kahana.

Devil Weed is a shrub with long rambling branches, its leaves are triangular shaped, opposite, with a toothed leaf edge. Leaves are also limp with velvety hair and have a distinct turpentine smell when crushed. The leaves have three thick veins shaped like a pitchfork, hence the common name “devil weed.” Flowers are held in small clusters, are pale purple to off-white, and usually have distinctive long stamens that can produce up to 800,000 wind dispersed seeds per plant.

Devil Weed is an aggressive colonizer of clearings and wet disturbed forests. It forms dense thickets 4-6 feet high that shade out other plants, releases toxins into the surrounding soil that reduces growth of native species, is toxic to livestock, and causes skin problems and asthma for people subject to allergic reactions.

The Oahu Invasive Species Committee advises anyone who finds Devil Weed to NOT REMOVE, pull or cut down the plant, but to text a photo and the location to 808-286-4616 or email Improper disposal could spread seeds. Let OISC the job.

The Oahu Invasive Species Committee (OISC) is a voluntary partnership of state, federal, and private agencies. OISC works to prevent the establishment of new alien pests, controls incipient pests on public and private land, and educates the community about the threats of invasive species and what they can do to help. Learn more about their important work at

Featured Posts
Check back soon
Once posts are published, you’ll see them here.
Recent Posts
Search By Tags
Follow Us
  • Facebook Basic Square
  • Twitter Basic Square
  • Google+ Basic Square
bottom of page