New thug in town - Dittrichia graveolens. How to get rid of it. And how to tell it from native Madia

Young Dittrichia graveolens, stinkwort, showing "Christmas tree" form

So I recently learned what that sticky smelly plant on my neighbor's grassy hill is. It's a very very bad weed! -- Dittrichia graveolens, commonly known as stinkwort. As editor of our local CNPS chapter's newsletter, I received a timely article from a member which solved that little mystery. The plant shown above is growing on that grassy hill today - but it won't live past tomorrow!

The content below pulls together two articles from the upcoming newsletter, text reused with permission, photos used with permission too. (Nice thing about the blog -- more room for photos.) It's good to spread the word widely about this widely spreading weed.

Wanted Dead or ... ... DEAD!

DITTRICHIA GRAVEOLENS, a.k.a. stinkwort, is a new invasive non-native plant to watch out for, first recorded in the early 1980s in Santa Clara County. It is a late-summer to fall annual that germinates over a prolonged period from May to September, putting it out of sync with the seasonal development—and control methods—of other non-native warm season annuals in the Asteraceae family. It has a heavy camphor smell - unmistakeable, and touching the sticky leaves can cause dermatitis in some, similar to poison oak rash (but not, in my experience, in very many people).

Last year's skeleton still shows the "Christmas tree" shape. Surrounded by seedlings.

At maturity, the plant is often the shape of a perfect Christmas tree. The tiny dandelion-like flowers are yellow and have ray and disc petals.

OCTOBER UPDATE: with more experience I now know that the below picture is of other seeds sticking to the stinkwort plant - which is very sticky. In fact one way to find it after thistles have gone to seed, is to look for the plant covered in thistle down.

Stinkwort seeds have seeds with hairs - but above is thistle down sticking to a stinkwort plant!
Photo credit: Toni Corelli

OCTOBER UPDATE: Here is a photo showing the seeds - the hairs are small, like the flowers:

Stinkwort flowers gone to seed - maybe half an inch across or less

The seeds are also dandelion-like but much smaller. The seeds are wind-borne and sticky. They adhere to vehicles and heavy equipment, promoting dispersal along roadways and onto well-intentioned reclamation sites. Stinkwort is unpalatable to wildlife and livestock, and can cause them problems if ingested.

Buds, flowers, foliage of stinkwort. Once it flowers you can't leave the plant lying where you pull it.
Photo credit: Toni Corelli

The flowers and foliage of stinkwort are similar to those of native tarweeds. See below for tips on telling them apart.

In small infestations the best method of control is hand pulling the young plants, preferably before they start flowering. If plants of Dittrichia are pulled when in flower they will continue to ripen seed even after they’re uprooted, so they should be bagged and disposed of and not left on the ground.

Uncontrolled, Dittrichia can convert large swaths of land to worthless monocultures.

OCTOBER UPDATE: To dispose of plants that have flowered, bag them, add a little water, seal the bags, and leave them rot. It is not clear how long you have to leave the bags. Up to a year perhaps. For large infestations the best you can do (after plants flower) is pile them up in a shady location out of the wind, where the spread is minimized, possibly covering with a tarp. The very best you can do is not let them go to seed next year. Seed life is probably three years though I recently heard it might be only two years - which is good news.

Click here to view the California Invasive Plant Council page on stinkwort, Dittrichia graveolens.
Click here to view a wonderful poster on this scourge, from the Cal-IPC site.
Click here to view my Sentinel article on stinkwort.

Native Tarweeds

Madia elegans with (closed flowers of) Clarkia rubicunda in my garden. Both are local wild natives where I live.

Tarweeds are warm season annuals in the Asteraceae family. Madia elegans (common madia), Madia sativa (coast tarweed), Madia gracilis (slender tarweed), and Anisocarpus madioides (woodland madia) are a few of our more common local tarweeds. They occur in disturbed areas, grasslands and woodland habitats.

Woodland madia, Anisocarpus madioides. Photo credit: Pete Veilleux, East Bay Wilds

Madias range in size from about six inches up to six feet tall. Their foliage is heavily glandular (sticky!) with a sweet fragrance. The flowers are yellow, with disc and ray flowers. Madia elegans flowers are showy and can have brown in the disc and base of the ray petals. Flowers range in size from small to large and showy.

These tiny flowers sit atop a large plant! Madia sativa, coast tarweed.

Wildlife relish the seeds, which are dark and up to half a millimeter in size. Native people ground the seeds for pinole, a kind of flour.

This is probably Madia Sativa. Possibly Madia gracilis, slender media, which looks like M. sativa, but is smaller.
It has to be admitted that most Madias don't have a very garden-worthy form, including Madia elegans. Better with other things in front, or in the far off.

Madias can resemble the non-native, invasive Dittrichia graveolens (stinkwort). Both have similar yellow flowers and glandular, sticky foliage and stems. The main difference between them is that the Madia receptacle (where flowers are attached) bears scale-like bracts that subtend (occur below) the disk flowers, while the Dittrichia receptacle bears minute hairs among flowers. In addition the fragrance of Madia is light and sweet, whereas Dittrichia has a strong odor of camphor.

So - Weed early and weed often!