Do NOT pull or cut down the plant. OISC will properly remove and dispose of the plant to prevent spreading seeds and re-sprouting.

Please report devil weed to OISC. Send photo and location to oisc@hawaii.edu or text 808-286-4616. You can also call our office at 266-7994.

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Devil weed (Chromolaena odorata)

Family: Asteraceae

Devil weed (A.K.A Siam weed, bitter bush) is a well-documented pest and is considered one of the world’s worst 100 invasive species. It is highly invasive and is on the Hawai’i State Noxious Weed List. Devil weed received an extremely high score on the Hawai’i Weed Risk Assessment (HWRA), suggesting it has the potential to be exceedingly invasive in Hawai’i.

Description:

Herb or shrub with long rambling branches

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 pitch fork, hence the common name “devil weed.”

Flowers are held in small clusters. Pale purple to off-white, usually with distinct long stamens.

Fruits are tiny and have soft white hairs, which allow it to be spread on the wind or water. The hairs also act like Velcro, attaching themselves to anything passing by.

Native to tropical America.

Harm:

An aggressive colonizer of clearings and wet disturbed forests, creating dense thickets that impede growth and regeneration of native species.

Forms dense thickets 4-6 feet high.

Forms thick canopy that shades out other plants.

Releases toxins into the surrounding soil, reducing growth of other plants.

Toxic to livestock.

Forms monocultures, reducing biodiversity.

Consumes large amounts of water and negatively affect soil nutrient levels.

Can host pests and pathogens of kava/awa (Piper methysticum).

Each plant can produce 800,000 seeds each year, which are readily wind dispersed.

Sand-grained sized seeds are also easily spread by birds and other animals when they eat the fruit, and by people when dirt or mud containing the seeds stick to shoes, clothing, equipment, or vehicles.

On O’ahu

First detected in 2011 at the Kahuku Training Area, devil weed is now found in Kahana Valley, Pūpūkea and most recently in ’Aiea (2015). Kahuku Training Area is also the weekend home of the Kahuku Motocross Track, popular with motocross and dirt bike enthusiasts and hunters. Decontamination of bikes and hunting gear after use is necessary to prevent it from spreading across O’ahu, as well as to other islands.

OISC’s management goal for devil weed is island-wide detection and eradication.

Early detection and reporting are essential. Please call OISC at 286-4616 or email oisc@hawaii.edu to report devil weed.

Pest Alerts and Publications:

For more information, see:

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