An Assessment of Exotic Plant Species of Rocky Mountain National Park
Linaria vulgaris P. Mill
Butter and eggs, yellow toadflax, wild snapdragon (Scrophulariaceae)
Current level of impact
Known locations in RMNP: Upper Hollowell Park, common around Beaver
Point, utility area. Found especially around old homesites.
Assessment: Several widespread and dense populations in park. When
added together, populations would cover an estimated area of 11-50 hectares.
Found in high quality areas with no known disturbance for last 100 years.
Potential to invade and modify/replace existing native communities.
Distribution
Origin: Eurasia, escaped ornamental.
Geographic distribution: Throughout most of temperate North America.
In Colorado found from 6000' to 8500', mostly on western slope but also found
on eastern slope.
Ecological distribution: Waste places, pastures, and roadsides. Cultivated
fields, meadows, gardens. Locally abundant and often found around sites of
former homesteads. Occurs in a wide variety of habitats, but is generally
limited in wet or dark conditions.
Soils: Occurs on mostly sandy or gravely soils. Common on chalky soils.
Reproduction
Perennial herb, reproduces by seeds and creeping rhizomes. Extensive, creeping
rhizomes. Production from shoots can be large, and may begin at seedling stage.
Plant is self-incompatible and insect pollinated. Flowers June-August.
Vegetative: Vegetative reproduction is important because of low seed
viability. Vegetative reproduction may begin as soon as 2-3 weeks after germination,
and is possible from root fragments as short as 1 cm.
Seed production: Range from 1,500-30,000 seeds/individual, but it is
often difficult to define an individual because of colony forming habits.
Seed dispersal: Seeds are winged which may allow for long distance
dispersal. Seeds may also be dispersed by water and ants.
Seed longevity: Seeds may remain dormant for periods up to 8 years.
Germination: Germination success is often below 10%, although it is
highly variable.
Competition
In North America, Linaria vulgaris is generally considered a strong
competitor, but is considered a weak to moderate competitor in Europe. Linaria
vulgaris is able to quickly colonize open habitats, and is capable of
adapting growth form to a wide range of conditions. Generally does well in
moist areas with high fertility but will be displaced by other species when
growing in less favorable conditions. Plants growing in dry soils tend to
be stunted, but are relatively persistent.
Level of impact: Persistent, aggressive invader and is capable of forming
colonies through adventitious buds from creeping root system. Seeds generally
germinate in the top 2-3 cm of soil, and also at the soil surface.
Competition
Once established, high seed production and ability to reproduce vegetatively
allow for rapid dispersal and high persistence.
Control
Extensive root system makes this species difficult to control.
Chemical: According to some studies, permanent long term control cannot
be achieved by herbicide treatments. L. vulgaris is resistant to many
chemicals such as 2,4-D amine and MCPA salt. Glyphosate, amitrole, diquat,
and picloram can be used for spot treatment. Glyphosate applied at early bloom
provided some current season control, but was followed by abundant regrowth
the following spring.
Mechanical: Generally the keys to controlling Linaria vulgaris
are to prevent seed production and promote root starvation which can be accomplished
by mowing and tillage (Saner et al. 1995). Tillage has been somewhat successful
in controlling L. vulgaris in crops. Tillage should begin on summer fallow
in June and continued at 3-4 week intervals. In post season cultivation, tillage
could begin as soon as crops are harvested and should continue at 3-4 week
intervals until shoots are killed by first frost. Mowing may also be used
to help decrease seed production but generally will not eliminate L. vulgaris
stands.
Cultural: Grasses can be used to compete with L. vulgaris. Disturbed
areas can be seeded with vigorous, well adapted grasses.
Biological: Biological control has been relatively successful for Linaria
vulgaris. In general, the root system seems to be the most promising target
that is susceptible to damage. Weevils (Gymnetron antirrhini) larvae
develop inside of the fruit, and adults feed on leaves, buds and stems. Harris
(1961) concluded that G. antirrhini is the most important agent for
biological control of L. vulgaris in the eastern provinces of Canada,
British Columbia, and the northwestern U.S. Other species that may be used
to help control L. vulgaris include another weevil (Mecinus janthinus),
leaf feeding moths (Calophasia lunula), and root mining moths (Eteobalea
serratella). Mecinus janthinus larvae bore in stems, and the adults
feed on shoots. Celophasia lunulahas become established in Ontario,
but other more northern releases have failed. Eteobalea serratella
winter as larvae in roots and damage plants throughout the growing season.
Other: Fire is not a recommended method of control for L. vulgaris.
Notes: Generally considered only moderately poisonous to livestock.
References:
Baig, M.N., K.N. Harker and A.L. Darwent. 1994. Tillage enhances yellow toadflax
(Linaria vulgaris Mill.) control with glyphosate. Weed Science Society of
America 34:16 (Abstract #47).
Carder, A. C. 1963. Control of yellow toadflax (Linaria vulgaris) by grass
competition plus 2,4-D. Weds 11:13-14.
Harris, P. 1961. Control of toadflax by Brachypterolus pulicatius (L.) (Coleoptera:
Nitidulidae) and Gymaetron antirrhini (Payk.) (Coleoptera L. Curculionidae) in
Canada. Canadian Entomology 93:977-981.
Morishita, D.W. 1991. Dalmatian toadflax, yellow toadflax, black hembane, and
tansy mustard: Importance, distribution and control. In James, L.F., J.O.
Evans, M.H. Ralphs and R.D. Child (eds.) Noxious Range Weeds. Westview Press.
Boulder, Colorado. 466 pp.
Saner, M.A. D.R. Clements, M.R. Hall, D.J. Doohan, and C.W. Crompton. 1995. The
biology of Canadian weeds. 105. Linaria vulgaris Mill. Canadian Journal of
Plant Science. 75:525-537.
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