(Sprengel) R. King and H. Robinson

eupatory, Crofton weed, sticky snakeroot, catweed, hemp agrimony, sticky agrimony, sticky eupatorium

Eupatorium adenophorum, E. glandulosum, E. pasadense

Ageratina herbacea, A. occidentalis, A. shastensis

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CalEPPC List B,CDFA nl

Marc C. Hoshovsky,Richard Lichti

Eupatory (Ageratina adenophora) is a shrub three to five feet tall with trailing purplish branches that root on
contact with the soil, resulting in dense thickets. The base of the plant is woody with a glandular-hairy stem. It seeds abundantly.

Eupatory is found in most California coastal counties, but is particularly common from the San Francisco Bay Area to Santa Barbara and in Riverside, Los Angeles, and Orange counties. It also occurs in the Mojave Desert and in the central Sierra Nevada foothills (Mariposa County). In California it generally is found below 1,000 feet elevation (300 m), but in northeast India it has been a problem at nearly 6,600 feet (2,000 m) (Baruah et al. 1993). Eupatory occurs mainly in creek beds and forest clearings, in areas with steep (more than 20 percent) slopes, or in disturbed areas. It prefers frost-free areas with abundant rainfall (Parsons 1992). It can be found in redwood forest and coastal canyon habitats; but is most seriously invasive in mild coastal riparian areas, forested areas, or grasslands (Erasmus et al. 1991).

Native to Mexico, eupatory is widely naturalized elsewhere. It was introduced to many parts of the world as an ornamental during the nineteenth century and is now an established pest in many tropical and subtropical areas, especially northeastern India, Nigeria,
Southeast Asia, the Pacific Islands, South Africa, New Zealand, and Australia (Morris 1989, Parsons 1992). It is unknown how or when it was introduced to California. However, by 1935 it was reported as a “rare escape” in the San Francisco Bay Area and along the south coast (Robbins 1940). In Australia it spread slowly at first. Following a ten-year drought, combined with overgrazing, the infestations expanded rapidly, overrunning large areas of dairy pastures and
horticultural land along the border of New South Wales and Queensland. Spread was so fast that in some areas farmers abandoned their holdings (Everist 1959, Dodd 1961).

Eupatory reproduces by prolific asexual
seed production and spreads by dispersal of seeds (Muniappan and Viraktamath
1993). Seeds are easily dispersed by wind and water because of their pappus of
hairs. Seeds are also spread as an impurity in agricultural produce, in sand and
gravel used for road making, in mud sticking to animals, machinery, and other
vehicles, and by adhering to footwear or clothing (Parsons 1992).

Eupatory is considered a serious weed in agriculture, especially
in rangeland, because it often replaces more desirable vegetation or native
species (Erasmus et al. 1991). It is fatally toxic to horses and most livestock,
and apparently is unpalatable to cattle. The toxic disease caused in horses,
known as “blowing disease,” may take several years to become evident. The
symptoms of coughing, difficult breathing, and violent blowing after exertion
are the result of acute edema (swelling) of the lungs, leading to hemorrhaging.
This plant may reduce growth of nearby vegetation by releasing inhibitors,
perhaps allelopathic compounds, into the soil. Eupatory is potentially a problem
weed in forestry (Morris 1989).

Buds appear in late winter and flowering begins in March. Seeds are set without pollination or fertilization, and some 15 to 30 percent of the 7,000 to 10,000 seeds produced by each plant are not viable. Seeds mature and are shed between April and mid-June, the lower leaves of the plant dropping after seed fall. Dense stands can contribute up to 60,000 viable seeds per square meter to the seedbank. Buried seeds lose their viability at a constant rate, averaging 20 percent of all viable seeds per year. Nevertheless, because of high seed production, this high mortality has little effect on the plant’s potential for spreading.

Germination occurs between June and March, with peak germination (over 80 percent of viable seeds) in August and September. Light is necessary for seeds to germinate, so unshaded conditions, such as bare soil, are essential for establishment. Eupatory does not invade managed, densely growing pastures. Once germinated, seedlings can withstand a considerable amount of shading, compensating for reduced light intensity by increasing leaf area. Deep shade, however, will kill seedlings. Seedlings grow rapidly and are fully established and able to regenerate from the crown, if damaged, within eight weeks of germination. In second-year and older plants, new growth begins with the first major summer rains, usually in June. Growth rate of seedlings and mature plants remains high during summer but tapers off in the cooler winter months (Parsons 1992).

Eupatory grows rapidly and produces many shoots and branches, which form dense thickets. Plant colonies increase in density and local coverage when bent-over and broken stems take root where they contact soil or when root fragments with attached crown pieces are moved during cultivation. Growth in this latter instance occurs only from buds on the fragment of the crown, not from the roots (Parsons 1992).

(click on photos to view larger image)

Mechanical control is
difficult because of the species’ preference for steep slopes. Where practical,
eupatory can be controlled by slashing followed by ripping or plowing and then
sowing other plant species to outcompete seedlings. This is best done in spring,
using crawler tractors and tandem offset discs (Parsons 1992).

Insects and fungi: No
insects or fungi have been approved by the USDA for introduction as biological
control agents against eupatory in the United States. However, most control work
on this species has focused on biological methods. In one study, the gall fly
Procecidochares utilis did not significantly reduce seed germination. However,
the galls produced by this insect did either temporarily stop growth or
completely killed growth of stems beyond the gall. In all cases the galls
resulted in the production of underdeveloped capitula and a reduced number of
capitula (Van Staden and Bennett 1990). This gall fly has been fairly successful in Hawaii, but its performance has been more variable in Australia due to parasitism by some indigenous hymenopterous insects (Parsons 1992).

Herbicides can be effective against eupatory. Parsons (1992)
recommends a label strength, high-volume application of glyphosate, or dicamba +
MCPA, or picloram + triclopyr in late summer or autumn when the weed is growing
actively. Plants should be thoroughly wetted, particularly at the base. In less
accessible, steep or rocky areas, treat scattered plants with granular
formulations of these herbicides, or use a gas gun and apply low-volume,
high-concentration treatments of picloram + triclopyr (Parsons 1992). Examine
labels for current registered uses of these herbicides in
California.åÊ