Baccharis pilularis
(coyote brush)

B.pilularis, commonly known as coyote brush, is an evergreen shrub native to Pacific coastal North America, Oregon and California in the USA, and northern Baja California in Mexico. There is little information to indicate the weediness of this species and very few reports of its establishment outside its native range, though the horticultural forms may be found elsewhere and it can be found in various botanic gardens around the world. B. pilularis is a pioneer species and can become abundant and dense in its native habitat where land is cleared or overgrazed. However, these situations can be prevented by good land management practices. Some sources refer to the erect form being invasive in areas of exposed soil, such as caused by overgrazing, changing fire regimes or clearing, but these are generally older sources (Leonard, 1957; McBride and Heady, 1968).

B. pilularis mostly occurs within its native or endemic range which is the coastal areas of Oregon, California and northern Baja California. There have been some plant specimens collected in Arizona and New Mexico; the specimen reported from New Mexico was regarded as a waif or weedy introduction (Flora of North America Editorial Committee, 2015; USDA-NRCS, 2015). Elsewhere there may be specimens in botanic gardens and the horticultural varieties used for ground cover may also have a wider distribution within the USA.

Given that B. pilularis is not known to have established or spread outside its native range and that present day requirements for national and international movements are much more stringent than in past years, the risk of introduction could be considered low. However one closely related congener, Baccharis halimifolia, has become a serious invasive weed in Australia, France, Spain, Russia and elsewhere in Europe (Palmer and Sims-Chilton, 2012; EPPO, 2013). It is thought that B. halimifolia was brought to Australia in the nineteenth century as an ornamental shrub for Brisbane gardens (Bailey, 1900; McFadyen, 1973). It was similarly introduced into Europe (Fournier, 1936).

B. pilularis is typically found in wooded or scrubby habitat and along coastal hillsides and canyons below 600 m (2000 ft) (Lady Bird Johnson Wildflower Centre, 2015). Baccharis pilularis subsp. pilularis is primarily found on sandy coastal bluffs and beaches in California (Flora of North America Editorial Committee, 2015) where it plays a role in soil binding. The erect subsp. consanguinea, is a dominant shrub in coastal sage scrub communities (Steinberg, 2002; Flora of North America Editorial Committee, 2015).

Genetics

B. pilularis has a chromosome number of n=9 (Raven et al., 1960; DeJong and Montgomery, 1963; Keil and Pinkava, 1976) which is also the most common number reported for other congeners though tetraploid and aneuploid species have been reported from Peru.

Reproductive Biology

The autecology of the congener, B. halimifolia, has been described (Westman et al., 1975) and this study could be used as an indicator for B. pilularis. B. pilularis is a dioecious species that flowers in autumn. Wind is the main pollination mechanism and female plants produce prolific quantities of seeds. The achenes are attached to a pappus and are wind dispersed. Seeds are not long lived and it would be unlikely that a viable seed store would build up from year to year in the field. Seeds may have a facultative light requirement for germination.

Physiology and Phenology

The phenology of the erect form has been described in detail by Hobbs and Mooney (1986).

Longevity

Plants live 10-20 years but basal sprouting and layering may extend this lifespan (Steinberg, 2002).

A large arthropod fauna is associated with B. pilularis (Tilden, 1951). Several species have been shown to be host specific including the cecidomyid fly Rhopalomyia californica and pathogen Puccinia evadens (Palmer, 1986; Palmer and Tilden, 1988; Ehler et al., 1990; Palmer et al., 1993).

Environmental

• Erosion control or dune stabilization
• Wildlife habitat

General

• Botanical garden/zoo

The erect form is not dissimilar to other Baccharis species, such as B. sarothroides (found in Arizona and New Mexico), B. neglecta (Texas), B. halimifolia (Gulf Coast and Eastern seaboard of the USA) and B. conferta (Mexico).B. emoryi is also found in some of its range and can be difficult to distinguish from B.pilularis subsp. consanguinea because identifiable characters such as plant height, leaf length, length of pappus and bract shape have overlapping values (Chester and Newell, 2006). Within its natural range along the western coast of the USA, it is unlikely to be misidentified for non-Baccharis plants as its morphology, evergreen nature, alternate leaf arrangement and dioecious habit make it quite distinctive. 

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Prevention and Control

B. pilularis is largely confined to its native range where it is generally not regarded as weedy. As there is little history indicating that it is a significant disperser or invader, specific measures to prevent dispersal or movement do not seem warranted. However, plants should not be moved to new areas without due assessment.

Within its native range, there are control techniques available should encroachment on grasslands be considered undesirable. Burning and controlled grazing have been suggested (McBride and Heady, 1968). Herbivory by small mammals in closed shrub stands may also be important in reducing the abundance of herbaceous species following shrub invasion in grassland (Hobbs and Mooney, 1986). Herbicides such as glyphosate are also available (Gambril, 1983; Mortenson, 1984).

Biological control could not be considered within North America because B. pilularis is a native, endemic species. However should B. pilularis ever become a serious weed over large scale areas on another continent then a suite of effective agents would be available for consideration. The most obvious choice would be the cecidomyid fly Rhopalomyia californica, which has been demonstrated to give significant control of B. pilularis in its native range (Ehler et al., 1984; Ehler, 1987) and also spectacular control of Baccharis halimifolia in Australia (McFadyen, 1985). A second potential agent is the rust Puccinia evadens. Both B. pilularis and B. halimifolia are hosts of this pathogen which has also contributed to the successful control of B. halimifolia in Australia. Other insect species found on B. pilularis would also be sufficiently host specific and laboratory evidence suggests that most of the 14 agents released in Australia for B. halimifolia (Palmer and Sims-Chilton, 2012; Winston et al., 2014) might also establish on B. pilularis.

Further research of the biology, autecology, and phenology of B. pilularis are needed.

20/08/15 Original text by:

Bill Palmer, Biosecurity Queensland, Brisbane, Queensland, Australia