Invasive Plants of California's Wildland

Erechtites glomerata
Asteraceae. Annual herb or weak perennial. Stems: 0.3-6.6 ft (10-200 cm) tall, erect from a deep, often branching taproot. Branches ascending, thinly villous to tomentulose. Leaves: alternate, oblong-ovate to lanceolate in outline, light gray-hairy, becoming somewhat smooth; 2.8-5.9 in (7-15 cm); lower leaves petioled, deeply pinnately lobed or pinnatifid, villous to tomen-tulose, becoming somewhat glabrous; upper leaves sessile, reduced, and pinnately to irregularly toothed. Inflorescence: heads in terminal, somewhat corymbose clusters or panicles; radial (discoid and salverform), involucre 0.2-0.3 in (5-8 mm) long, cylindrical, stalked. Phyllaries in 2 unequal series, oblong, glabrous to thinly tomentulose, outer much shorter than inner, apices acute. Flowers: two forms, outer pistillate, inner bisexual, corollas tubular, pale or dull yellow. Fruit: achenes 0.04-0.08 in (1-2 mm) long, cylindrical, ribbed; pappus 0.2 in (5 mm) long, white, composed of fine capillary bristles. Flowers in California from April to October (Robbins et al. 1941).

E. glomerata (left), E. minima (right)

Erechtites minima
Asteraceae. Annual herb or weak perennial. Habit and size similar to Erechtites glomerata , but subglabrous to obscurely puberulent. Leaves: arachnoid (cobwebby) beneath, linear-lanceolate, evenly and finely dentate, 2.8-7.9 in (7-20 cm), not lobed or pinnately cleft. Inflorescence: large, to 30 cm broad. Flowers: pistillate, pappus 6-7 mm long (Robbins et al. 1941).

Both species occur occasionally along the coast at low elevations (<500 m) from central Oregon to Santa Barbara County and the Channel Islands. They are found primarily in disturbed areas, especially roadsides, stream banks, pastures, and as post-burn opportunists. They tend to prefer grasslands, woodlands, and coastal scrub habitats (Hickman 1993). Australian fireweed has been reported from redwood forests on the North Coast (Robbins et al. 1941). Although ubiquitous, Erechtites species do not now represent a major ecological threat to native plant communities on California’s north coast (Popenoe 1999). They invade areas following clearcut logging operations, sometimes dominating overall plant cover, but other shrubs and trees typically replace them in about five to ten years (Muldavin et al. 1981). Martin and Popenoe (1984) found buried seed of Erechtites to be more abundant than seed of any other species in old-growth redwood forests of Redwood National Park. Combined average seed density for the two species was 522 per square meter in old-growth blocks in the vicinity of recently harvested clearcut second growth.

Erechites species can grow in a variety of climates. Muldavin et al. (1981) found E. minima in clearcuts with compaction and topsoil removal. They apparently are well suited to exploit fertile, freshly disturbed ground, but are demanding of nutrients and are weak competitors. Erechtites plants are uncommon in north coast vegetation types until competing vegetation is removed, either mechanically or by fire. The plants are also uncommon along roads where soil is compacted or topsoil has been removed.

Both species are native to Australia and New Zealand. Australian fireweed was naturalized in Humboldt County by 1918 (Robbins 1940). It has become naturalized on the West Coast only in southern Oregon and California. Cutleaf fireweed was reported before 1941 in redwood forests from Mendocino to Del Norte County (Robbins et al. 1941). Plants spread by wind dispersal of seeds.

Erechtites species quickly dominate grasslands and fields, and they are among the most serious plant pests in Channel Islands National Park (Halvorson 1992).

Little information is available on growth and reproduction of either species. A related species, Erechtites hieracifolia, is better known and may have similar characteristics.

In germination studies of Erecthtites hieracifolia, a close relative of Australian fireweed, Baskin and Baskin (1996) found that if conditions were not favorable for germination during the late summer and early fall, about half of the seeds at maturity in September became dormant. These seeds would not germinate under any test conditions, whereas the other half of the seeds would germinate under only a narrow range of test conditions. Australian fireweed flowers in July-September; cutleaf fireweed flowers in June-August (Allen 1997).

Erechtites sp.

In germination studies of Erechtites hieracifolia , Baskin and Baskin (1996) found that half the seeds at maturity in September would not germinate under any test condition, whereas others would germinate under only a narrow range of conditions. Seeds appear to need minimal temperatures to germinate, such as conditions in spring. Since 89 percent of seeds were viable after eight years of burial, it appears that, although seeds of this species are wind-dispersed, they also have the potential to form a long-lived seedbank. Thus, soil disturbance at any time from May to September could result in establishment of plants from seeds. Australian fireweed has been reported to be facultatively mycorrhizal, which may explain its rapid invasion capabilities in relatively arid grasslands on San Miguel and other coastal California islands (Allen 1999).

Erechtites minima

On the Channel Islands cutleaf fireweed apparently does not need disturbance to become established (Halvorson 1992). Elliott et al. (1997) describe Erechtites species as early successional and shade-intolerant. Optimum conditions for E. hieracifolia growth occurred at soil pH 5.3 to 5.5 (Stephenson and Recheigl 1991). At Point Reyes National Seashore, Australian fireweed commonly sends roots into the soil or into rotting wood from any stem that has been laid on the ground either by heavy rain or the weight of its long (to six feet) stems. Rooting stems continue to grow either vertically or horizontally. Many branch further to produce what looks like an entire flowering plant connected to its neighbor by one stem (Allen 1999).

(click on photos to view larger image)

Erechtites species tend to exhibit moderate to rapid rates of infestation, particularly after fire. In less than one year of initial establishment on San Miguel Island, Santa Barbara County, in 1984, cutleaf fireweed spread to cover 173 acres (70 ha) with a maximum density of 3,237 plants per acre (8,800/ha). Within a year of the Vision fire in October 1995 at Point Reyes National Seashore, thick stands of Australian fireweed dominated the burned areas where native bishop pine seedlings were reestablishing. Over 1.2 million plants of Australian fireweed were removed in 1996 (Allen 1997).

Monitoring three times a year is suggested because of the large seedbank. Disturbance caused by removal efforts could exacerbate the infestation.

Manual methods: Channel Islands National Park uses volunteers to manually remove cutleaf fireweed (Halvorson 1992).

Insects and fungi: No biological control agents have been approved by the USDA for use on Erechtites species.

Plant competition: Popenoe (1999) suggests that control experiments might try to examine nutrient requirements and ability to compete. Success might be possible by decreasing nitrogen availability by mulching with sawdust, and sowing or planting natives to increase competition. Natives might have a better chance of successful competition if they are innoculated with mycorrhizae to increase their hold on available nutrient pools.

No information on chemical control of these species is available. Herbicide effects may be similar to those for Erechtites hieracifolia. Olney (1971) reported that atrazine gave excellent control of E. hieracifolia, whereas diuron was ineffective. Herbicides were applied as directed sprays to E. hieracifolia in Hawaii. Diuron at 4 lb/acre gave excellent control for twenty weeks in both trials. Linuron at 4 lb/acre gave comparable results (Higaki 1973). In Indonesian tea plantations, three liters of glyphosate in 700 liters of water/ha completely controlled Erechtites species (Sukasman 1979). Check with a certified herbicide applicator to assess current chemical methods registered for the habitat type at any site at which removal of E. minima or E. glomerata is desired.