STICKY EUPATORIUM Also known as Crofton weed, eupatory, thoroughwort Ageratina adenophora (formerly Eupatorium sp.) Sunflower Family (Asteraceae) DESCRIPTION This perennial herb or semi-shrub is found on moist, exposed slopes and dis- turbed areas, particularly in riparian habitat and in forest clearings. Sticky eupatorium often has a straggly appearance and typically grows 3–5 feet SHRUBS tall. The stems are long and dark red with downy hairs, and woody at the base. Sticky eupatorium grows rap- idly, its shoots and branches forming dense thickets. Leaves are opposite moisture. In addition to being a wild- and triangular-ovate with toothed land weed, sticky eupatorium is an margins. They are about 2 inches long, agricultural weed and is toxic to horses and dark green, and glossy. unpalatable to cattle. REPRODUCTION KEY FACTORS Sticky eupatorium spreads primarily by asexual u Prolific seed production and rapid growth. seed production. Small, white or pinkish inflo- u Seed viability thought to be 2–3 years. rescences resembling pincushions appear in u Thrives in moist drainage areas. terminal clusters in March. From April to mid- June each plant produces 7,000–10,000 tiny u Resprouts from roots and from stems in con- black seeds, although up to a third of these are tact with soil. not viable. Each seed is topped with fine hairs TREATMENT OPTIONS that aid in wind dispersal. The seeds are easily u Pull plants by hand or dig them out with a airborne or dispersed by water,but they can also Pulaski when the plant is in flower but before it stick to clothing, footwear, or passing vehicles has gone to seed. Removing sticky eupatorium and animals. Most germination takes place in by hand is time-consuming.Although the root August and September, and seedlings are capa- system is shallow,stems break easily,especially ble of reproducing vegetatively within 8 weeks on drier soils, so care should be taken to pull of germination. The plant can also reproduce from the base of the stems so as not to leave from the roots and through parts of the stem root fragments. In moist drainage areas, you that touch the ground. might find yourself pulling up heavy, sodden IMPACTS clumps of root mass and soil. Often you’ll find Sticky eupatorium crowds out native plants that the roots form a continuous mat.However, after fire disturbance or flooding, and is very it’s important to get the root mass, as the plant competitive with natives in areas with summer will otherwise resprout. 70 WEED WORKERS’ HANDBOOK u Brush cut sticky eupatorium on dry, steep FOLLOW-UP slopes and in drainage areas, using a rotary If the infestation is a manageable size, follow slash brushcutter.Some practitioners then fol- brushcutting with removal of the roots. Alter- low up by digging out the roots; others, by natively, if it is safe to use herbicide, you can spraying the cut stems with herbicide. In the wait for lush growth to return after brushcut- Marin Headlands repeated brushcutting at ting and spray the plants in order to finally kill monthly intervals in the drier months has them. Return to the site 2–3 times after the ini- proved unsuccessful in exhausting the root tial visit (at 6-month intervals) to scrape off any system and preventing the stems from new seedlings from the soil surface with a resprouting,perhaps because of the additional McLeod or hula hoe. Mulching the weeded area moisture supplied by summer coastal fog. with a 1- to 2-inch-thick layer of straw or cover- u Foliar spray. Some practitioners have have ing with landscape fabric will help prevent the had success by spraying a weak solution of seedbank from germinating and will make fol- glyphosate in infestations on dry slopes away low-up much easier. from water. Spray the tops and undersides of the leaves (either before or just after the INTERESTING FACTS plants begin to show buds). Originating in Mexico, sticky eupatorium is SHRUBS considered a major agricultural weed around DISPOSAL the world. It may have been introduced to Stems will easily reroot in water, so make brush California as an ornamental plant. In India the piles well away from wet areas. Piles can be left plant is being used to produce a green commer- to decompose on site. cial dye,while in Nepal the plant juice is applied to cuts and injuries.Studies show that compost- ing sticky eupatorium for approximately 2 months eliminates its toxins. Notes THE PLANTS: HOW TO REMOVE BAY AREA WEEDS 71.