Dalmation Toadflax 
(Linaria dalmatica)

By: Erica Hagerman                                                                                                                  


<www.agf.gov.bc.ca/cropprot/weedguid/dalmtoad.htm>
   

     

Introduction

   
 toadflax (Linaria dalmatica) is a noxious weed that was originally introduced as an ornamental plant from the Mediterranean region of Europe. The plant was first introduced to the West Coats of North America around 1874 (Sheley & Petroff. 1999) and is often mistaken for snapdragons. Dalmation Toadflax is closely related to Yellow Toadflax, and the two species share many of the same characteristics.

Identification


 Toadflax can grow to be 4 feet tall. Leaves are bluish green, with hints of red on the underside and edges. The sessile, waxy leaves are commonly described as egg, lance or heart shaped. Flowers of the Dalmation Toadflax strongly resemble those of Snapdragons. The inch long flowers are bright yellow, and some have a hint of reddish/orange in the center of them.

Background


 Toadflax is a prolific seed producer and has a complex root system. It can also reproduce vegetatively, which allows it to spread quickly. The weed was said to have evolved in moderately to intensely grazed areas. Once established in plant communities it is difficult to control due to its extensive root system and prolific seed production, as mentioned above (Lajeunesse. 2004). An integrated management plan is needed to increase the successfulness of controlling this weed. 

Habitat and Distribution


 Toadflax can be found throughout most of the U.S. as well as Canada (Sheley & Petroff. 1999). Areas where this weed can be found include; pastures, arid rangelands, railways, waste areas, roadsides as well as other disturbed areas. (University of Idaho Extension. 2002).


                                                                                                                               
                       <http://www.plants.usda.gov>

Biology and Ecology


 plant is a short-lived, trailing perennial that reproduces through the dispersal of seeds and trailing lateral roots (Idaho’s Noxious Weeds, p.11). Seeds with irregular wing angles are formed in a pod that is ˝ inch long. The seeds can remain viable in soil for nearly ten years. Dalmation Toadflax plants generally have a 3 year lifespan and are capable of producing almost half a million seeds. The deep, complex root system of plant is well adapted for harsh environments, and helps it to compete well with other plants (especially shallow rooted perennials). Due to its root system and large amounts of seeds produced, it is difficult to control this weed (State Noxious Weed Control Board. 2003 ).

Ecological and Environmental Impacts


 toadflax has a negative effect on plant communities due to its strongly competitive nature. It easily takes advantage of disturbances to native plant communities. The weed can be a problem to soil stability on steeper slopes if it takes over the established bunchgrass/sod communities, it will increase erosion and surface runoff of water. However, dalmation toadflax has been credited to increasing soil stability in harsher, less vegetated areas. The weed is also thought to be a wintering site for the cucumber mosaic virus and the broad bean wilt virus, which are detrimental to agricultural crops (Lajeunesse. 2004).

Economic and Human Impacts Options
Economics:
Dalmation Toadflax is a noxious weed that can be costly as well as difficult to control due to its genetic diversity, extensive root system, and adaptability to diverse, localized habitats/climates (Lajeunesse 2004). Management costs can vary given the nature of control and the equipment and methods of application. The displacement of desirable plants can cause the loss of valuable forage. An estimated cost of having Dalmation Toadflax on rangeland is $5.25/acre (loss of forage), while direct management costs were approximately $40/acre (Lajeunesse 2004). As with most weeds, an integrated management system is the best method for control, since most other methods will not eliminate the weeds on their own.

Human Uses:
While Dalmation Toadflax is generally thought of as a noxious weed, it is not completely worthless to humans. Humans use Dalmation Toadflax for ornamental purposes, folk remedies/natural medicines, yellow dye, insecticide, as well as value it for its spiritual and magical characteristics (Lajeunesse. 2004). Even though there are uses for this weed, it is generally thought best to control it as soon as possible due to its ability to spread rapidly and displace native vegetation.

Management Options


 Prevention:
Due to the relatively unpredictable nature of Dalmation Toadflax, it is difficult to manage and prevent the weed from invading and spreading in a plant community. Dalmation Toadflax is known to thrive in well drained, arid regions, and is commonly found in sandy, coarse textured soils. Open rangelands and plant communities with low competition among species are also subject to invasability from this weed. Even healthy plant communities are prone to dalmation toadflax invasion since it is a very efficient competitor. Once it is established, it is unlikely that it will be eliminated simply by competing with native plants. Control methods are generally needed to eliminate these weeds.

Grazing:
Dalmation Toadflax will reduce forage value, and is generally not thought to be grazed by cattle to a great extent, though cattle have been known to browse the weed. Not much is really known about the digestibility and palatability of the weed in cattle or other wildlife, although sheep and goats will eat it and are beginning to be used as a control method. A range area was stocked with 1,000 ewes and lambs with 25-100% dalmation toadflax density. The sheep didn't eat large quantities of the plants at first, but eventually began to consume larger amounts, causing a decline in the weed density (Lajuenesse. 2004). Dalmation Toadflax is thought to be mildly toxic and unpalatable to cattle if eaten in large amounts. Reported cases of toxicity in cattle are rare, as they will generally avoid eating this weed. Sheep and goats can consume the plant without suffering any toxic side effects.

Mechanical/ Physical: 
Mowing Dalmation Toadflax is not very efficient since most means of spread are by its extensive root system. Cultivation and hand-pulling (small infestations) have limited success, since the process must be repeated for at least 5-6 years to make sure the root systems have been eliminated. Seeds can remain viable for at least 10-15 years; so further monitoring is required to prevent new infestations (Lajeunesse 2004).

Biocontrol:
There are several biocontrol agents that have been introduced to control both Yellow Toadflax (a closely related noxious weed) and Dalmation Toadflax, however the effectiveness of the agents is not well known. A defoliating moth (Calophasia lunula), an ovary feeding beetle (Brachyplerolus pylicarius), 2 seed capsule feeding weevils (Gymnaetron antirrhini &Gymnaetron netrum), a stem boring weevil (Mecinus janthinus) and a root boring moth (Esteobalea intermediella) are all introduced biocontrol agents (Beck 2001).

Chemical Control:
Herbicides with broadleaf focusing components such as dicamba or picloram have been used against this weed (Beck 2001). The effect of chemicals on this weed are variable from site to site. There is no guaranteed control method since what may work in one area may not in another. Application of picloram at 1 lb ai/ac during the fall is generally effective for up to 3 years, or the application of picloram at a lower rate of .5 lbs. ai/ac is said to be effective for up to 2 years. Dicamba is applied in the fall or pre-bloom at a rate of 4 lbs. ai/ac. Glyphosate is used for spot treatments of the weed in small areas (Sheley & Petroff. 1999). However, the effectiveness of chemical control relies upon the frequency and repetition of the applications as well as integrating it with other management strategies.

Fire:
Burning Dalmation Toadflax is generally not a good control method since it increases Dalmation Toadflax's ability to compete with other vegetation and creates disturbance (Lajeunesse 2004).

Additional Resources


 Sherry. Montana Weed Control Association. www.mtweed.org/Identification/PROJECT/project.html> Accessed 2004 April 14.

Ministry of Agriculture, Food & Fisheries. Pest Management. <www.agf.gov.bc.ca/cropprot/weedguid/dalmtoad.htm> Accessed 2004 April 16.
 
University of Idaho Extension. (2002). Idaho’s Noxious Weeds: Official State List. pp.11.

Lajeunesse, Sherry. 1999. Dalmatian and yellow toadflax. In: Sheley, Roger L. Petroff, Janet K., eds. Biology and management of noxious rangeland weeds. Corvallis, OR: Oregon State University Press: 202-216.

State Noxious Weed Control Board. (2003). <www.nwcb.wa.gov/weed_info/toadflax.html> Accessed 2004 April 16.

USDA-NRCS. Plants Database. Accessed 2004 April 11. <http://www.usda.gov/cgi_bin/plant_profile.cgi?symbol=LIDA>