Invasive Plants of California's Wildland

Ox-eye daisy (Leucanthemum vulgare) is a prostrate herb with stems that sprout laterally from a creeping rootstock. When in flower, the plant’s height ranges from one to three feet. The white-petaled flower-like inflorescences have yellow centers. Leaves are dark green on both sides, one to two inches long, smooth, and pinnately lobed or toothed. The number of flower stalks ranges from one to forty per plant.

Ox-eye daisy is found in both the North Coast Range and northern Sierra Nevada from sea level bluffs and canyons to “alpine” mountain meadows to 7,000 feet (2200 m) and from central California into Oregon. It is also common from the northeastern seaboard through the Midwest. Ox-eye daisy is also a problem at Rocky Mountain National Park (USGS 1999). It is a common weed of disturbed areas such as roadsides, fields, and pastures and former homesteads (Cowell 1973, Peck 1993). It readily spreads into wildlands. Ox-eye daisy is found in a variety of plant communities including, prairie, scrub, wet meadows, riparian forests, and open-canopy forests. It thrives in a wide range of conditions and in full sun to semi-shade. Plants are shallowly rooted to three inches (7.5 cm) deep and tolerate a wide range of soil moisture conditions, but do particularly well in soils that are heavy and damp (Parsons 1992).

Ox-eye daisy is native to Europe (Polunin 1969). It was probably introduced to North America as an ornamental early in the twentieth century. It is currently used as an ornamental, and is it often sold commercially in seed packets labeled as wildflower seed. Ox-eye daisy spreads through abundant seed production and vegetatively by rooting underground stems (rhizomes) (Griswold 1985). Seeds have no special adaptations to aid dispersal, but are small and fall to the ground up to two meters from the parent plant. When the flowerheads are dry, the seeds drop or are shattered easily by touch or movement. Water, human and animal foot traffic, and cultivating and earth-moving machinery can carry seeds into new areas.

Ox-eye daisy displaces native plant species, growing so densely it excludes other vegetation. It is not known to be used as forage by animals in California. While not considered poisonous to cows, it does impart a disagreeable taste to their milk. Ox-eye daisy is a host for several viral diseases affecting crops, including the yellow dwarf virus of potatoes (Parsons 1992). It is difficult to control or eradicate because of its large seedbank, long viability of seed, and ability to resprout if not completely removed.

Ox-eye daisy is capable of reproduction the first summer after it becomes established, regardless of plant size. Plants one inch in diameter have been observed bearing a single flower. Stem growth is prostrate and creeping until development of erect flowering stalks one to three feet (30-90 cm) tall. Flowering commences in late spring (May) and continues until late summer (August). Seed production is prolific when water is adequate. Most ox-eye daisy seeds remain viable for twenty years in the soil, and can remain viable after passing through digestive tracts of animals (Parsons 1992). Seeds germinate continuously as long as there is adequate moisture, fall through late spring in coastal regions. Plant growth slows during periods of flowering and low water availability.

Seed germination is inhibited by continuous darkness but otherwise not affected by variation in light (Thompson 1989). Studies have indicated that ox-eye daisy seedling germination and frequency are greater under increased moisture in hollows versus ridges, but dense groundcover can prevent ox-eye daisy establishment (Reader 1991).

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Ox-eye daisy can grow year-round, and its lifespan is indeterminate. Maximum growth has been observed in coastal regions at onset of cool fall weather, through winter and spring, just before flowering stalks shoot up. Aerial growth dies back after seed release. Vegetative growth slows in summer during and after flowering (Cowell 1973).

Little information has been published on mechanical, cultural, or biological control of ox-eye daisy. An important consideration is that seeds remain viable in soil for at least two years.
The first step in the control of ox-eye daisy is to develop a containment strategy. Removal methods will depend on environmental variables and the type of plant community infested. Primary methods of dispersal besides seed drop should be identified. If plants are growing along trails, shoes and hooves picking up seeds in wet soil may disperse them. People also pick the bright flowerheads, from which ripe seeds may fall as they hike through the region. Information about the daisies should be posted to alert wildland users. Small outlying populations should be treated first.

Complete eradication of a large, well established, and geographically widespread population of ox-eye daisies can be difficult because of their small size and abundant seed production. Prolific seed set and the ability of rhizomes to resprout make successful removal dependent on appropriately timed treatment and persistent follow-up. Removal sites should be inspected before plants have set a new crop of seed in June. If the infestation is small it may be difficult to locate the previous year’s removal site, so the site should be mapped and marked with colored flagging or pin flags, especially if follow-up will be done by someone else. If plants are mulched, the mulch will serve as an effective indication of the location of the infestation. It is much easier to locate daisies after flowering begins, which is typically by mid-June in coastal California populations.

Manual methods: A combination of hand removal and mulching is used to control ox-eye daisy in the Golden Gate National Recreation Area (GGNRA). If the infestation is small (less than 0.25 acre) or widely scattered, hand removal may be efficient. Using a small hand pick, chip around the base of the plant several inches deep to loosen the plant. Then lift the entire plant out intact without leaving any stem pieces (rhizomes) behind. Check for rhizome fragments, since an entire plant can regenerate from them. A round-point shovel is effective for scooping out whole plants. If the soil is flat and compacted, a sharp garden spade can also be used to scrape the plant out of the soil. A hula hoe is also handy for scraping away abundant masses of seedlings or small plants.

Mechanical methods: In Australia shallow cultivation of less than six inches (15 cm) was found to have little effect and was likely to spread roots. Cultivation greater than six inches in summer exposes roots to desiccation. Subsequent shallower cultivations kill seedlings. This technique opens the soil to infestation by other weeds and must be combined with dense revegetation with desirable seed (Parsons 1992).

Mulching: The most successful non-chemical method found for removing large infestations in GGNRA is to mulch heavily. Habitat Restoration volunteers at the GGNRA have successfully eliminated masses of mature and immature plants through the application of rice straw. One application 3-4 in (7.5-10 cm) thick when compacted was successful in two plant communities in the Marin Headlands: coastal scrub and wetland. Straw should be applied in fall at the onset of the growing season. One bale will cover approximately 100 square feet. The site should be monitored in early spring. If any live plants are found under the straw, or any light can reach the soil, then another thick layer should be applied before flowering begins in May. Native perennial plants at the Marin Headlands site came up through the straw, while the ox-eye daisy did not. This is because ox-eye daisy is a prostrate plant except for its flower stalks. Ox-eye daisy was observed to rot under the dense mulch maintained throughout the winter. If the infested area has a lot of woody plants they can make it difficult to mulch thickly and lopping or brush cutting may need to be undertaken first. Certified rice straw was used to avoid introduction of terrestrial weed seeds. Other mulches have not been tried. Wood chips might also be effective if they are applied thickly enough.

Winter monitoring is critical for mulched treatments in order to assess the condition of the mulch before growth surges in spring. If ox-eye daisies are seen growing through the mulch, it may have to be applied again. Check to see if the plants are seedlings or adults. When mulch is adequately applied the first time seedlings should not grow through it. Humans or animals may have passed through the area and disturbed the mulch. Where mulch is thinning, it should be re-applied, especially if there is a month or more of wet weather to come, or if the site is a wet habitat. Once a mature population is removed from the area, a crop of seedlings will take their place. Therefore, the length of time the area should remain mulched depends on the size of the seedbank and longevity of ox-eye daisy seeds in it. Along edges that are difficult to mulch, spot removal can be done by hand.

Prescribed burning: This approach has not been assessed for ox-eye daisy.

Insects and fungi: Biological control has not been investigated for this species.

Grazing: Intensive cattle grazing is an effective control for ox-eye daisy. Although cattle tend to avoid it because of its high acidity, under high stock density in an intensive grazing system, cattle eat this species (Wallander et al. 1991).

Picloram, imazapyr, sulfometuron methyl, and dicamba are effective at label concentration when applied in the early flowering stages, but these herbicides persist in the soil (Parsons 1992). Ox-eye daisy is moderately resistant to MCPA, 2,4-D, and dicamba (Stubbendieck et al. 1992), and these herbicides may damage non-target species.