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Stinkwort (Dittrichia graveolens)

Sunflower Family (Asteraceae)

Dittrichia graveolens (stinkwort). Copyright 2006 Tom Cochrane, CalPhotos.org
Photo: Copyright 2006 Tom Cochrane, CalPhotos.org


Dittrichia graveolens (stinkwort). Copyright 2006 Tom Cochrane, CalPhotos.org
Photo: Copyright 2006 Tom Cochrane, CalPhotos.org

Description/Habitat:  Stinkwort (Dittrichia graveolens) is an erect, fall-flowering, aromatic annual with a distinct camphor odor that reaches approximately 1m tall, with sticky, glandular-hairy foliage. It is native to Northern Africa, the Middle East, India, and southern Europe. Stinkwort inhabits disturbed places, roadsides, pastures, fields, riparian woodlands, levees, washes, and margins of tidal marshes, primarily in the San Francisco Bay region, especially the southern portion. Stinkwort was first found in California in 1984, and it has currently been spreading in Santa Benito, Santa Clara, and Santa Cruz counties. Stinkwort’s range appears to be expanding rapidly.

It was found on Fort Ord National Monument in 2011, and believed to have come in from a gravel delivery used for road and trail maintenance. The arrival of stinkwort was caught early before it could travel further into Fort Ord National Monument. If undetected, stinkwort can invade and take over any disturbed area. Stinkwort appears in places with an annual rainfall of at least 30-50 cm and makes land unsuitable for grazing, hiking, and numerous other activities due to its effects on humans and animals (see warning below).
Warning! Touching stinkwort can cause dermatitis, itchy skin, or blistering. Grazers that eat this plant can produce tainted milk or meat. When the seeds are ingested by grazing animals they can cause inflammation of the small intestine, and can lead to pulpy kidney disease or sudden death.

Leaves:  Stinkwort has sticky, slightly glandular foliage. The foliage is a light grayish-green color, and the stems and branches are covered with sparse alternate linear leaves that are 1- 4cm long and 0.1- 0.8cm wide throughout.
Flowers:  Flower heads are about 5-7 mm in diameter, consist of short yellow ray flowers, and can have yellow to reddish disk flowers. Mature, large plants can produce 500-700 flowers per plant.
Seeds:  Produces small, fluffy, light brown seed heads from October through December, and can produce seeds when the plant is only 2 cm tall. Each flower on the plant produces up to 50 viable seeds, and each mature, large plant (approx. 500-700 flowers) can produce up to 25,000-35,000 seeds. Stinkwort seeds are viable for 3 years, and spread by wind, water, machinery, animals, and human activities.
Flowering Period:  Germinates during May-June, actively grows during August-October, flowers from approximately September-December, and produces fruit from October-December.
Management:  The most effective treatment method for stinkwort is to handpull plants prior to flowering. This is the primary treatment method used on Fort Ord National Monument land. This method works best when small numbers of plants are present. Even when pulled, mature and flowering stinkwort plants can use remaining energy to produce seeds. For this reason, all plants in flower or seed should be bagged and disposed of in a way that will prevent seed spread.
Another method would be to use herbicides. Spraying stinkwort is probably the best option for controlling large infestations, but this can be problematic due to the oily/waxy coating on the leaves which can impede herbicide absorption into the plant. Herbicide can be used from mid-summer to early fall but applications have been shown to be more effective on younger plants and less effective on older plants. An herbicide application on older plants stimulates seed production while the plant is flowering, but the seeds produced are not viable. At this point we have not considered using herbicides as a method of controlling stinkwort at Fort Ord National Monument because the populations present are small enough to pull by hand.

To prevent the spread of stinkwort, monitor disturbed areas for new weeds, check grasslands and pastures regularly for signs of over-grazing, get gravel and other fill products from certified weed-free companies, wash and wipe off vehicles, bikes, pets, clothes, and boots after going through areas with weeds, and educate others about this weed.

DiTomaso, J. M. and E. A. Healy. 2007. Weeds of California and Other Western States. Volume 1: Aizoaceae to Fabaceae. University of California Department of Agriculture and Natural Resources: 350-352

Last updated: 08-20-2012