Dalmatian Toadflax and
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| STOP THE SPREAD |
W-1239, December 2002
Rodney G. Lym, NDSU Department of Plant Sciences
Both Dalmatian and yellow toadflax are escaped perennial
ornamental plants which were introduced in the mid-1800s (Figure
1). Dalmatian toadflax is native to the Mediterranean region
while yellow toadflax is from Eurasia. Yellow toadflax was first recorded
in North Dakota by H. L. Bolley from a collection made in
Fargo. The first record of Dalmatian toadflax is from Walhalla in
Pembina County in 1937 by O. A. Stevens. Dalmatian toadflax seedlings
are relatively poor competitors with grass species; but once
established, the weed can become extremely invasive, especially
on dryland sites, disturbed areas, and roadsides. Yellow toadflax
is adapted to more moist sites than Dalmatian toadflax, and is
often found in pastures, meadows, and ditches. Once an area
becomes infested, both species can dramatically reduce forage
production and decrease native plant and wildlife habitat.
Figure 1. Dalmatian (left) and yellow toadflax (right) plants look similar from a distance. (click on left photo to link to 83KB image of Dalmation toadflax) (click on right photo to link to 35KB image of yellow toadflax)
How do I identify these plants? Dalmatian and
yellow toadflax are members of the snapdragon family and thus
easily recognizable by the bright yellow flowers which have
swollen corolla-tubes that flare into two `lips,' with an orange colored
throat (yellow toadflax) and long spur (Figure 2). The flowers are 1 to
1.5 inches long with many flowers on a raceme. Both species have
an extensive creeping rhizomatous root system that spreads like
leafy spurge. The most distinctive difference between the species is
that Dalmatian toadflax has broad, heart-shaped leaves that clasp
a woody stem; whereas, yellow toadflax has narrow, linear
leaves with a narrow stem (Figure 3).
Figure 2. Dalmatian (left) and yellow toadflax (right) flowers are similar. Both are bright yellow with a long throat or spur, but yellow toadflax often has an orange center. (click on left photo to link to 38KB image of Dalmation toadflax flowers) (click on right photo to link to 35KB image of yellow toadflax flowers)
Figure 3. Dalmatian toadflax (left) has broad heart-shaped leaves, while yellow toadflax leaves (right) are long and narrow similar to leafy spurge. (click on photo to link to 25KB image)
What is Dalmatian and yellow toadflax's growth
cycle? The plants begin regrowth from the roots as soon as
the soil warms in early spring. Toadflax flowers from late-June
through August in North Dakota and single plants may produce
over 500,000 seeds which are dispersed by wind, rain, wildlife,
and movement of forage and livestock (Figure 4). The seed is
disk-shaped 0.08 inch diameter, dark brown to black, and often
have irregular papery wings. Seed dispersal begins a few weeks
after flowering and continues into winter. The roots of a single plant
can extend 10 feet and give rise to daughter plants every few inches.
Figure 4. Toadflax seed are dark and disked shape with wings. (click on photo to link to 49KB image)
Why is this plant a concern? The toadflax species are aggressive and will displace forage in pasture land and native species in wildland. Yellow toadflax can be mildly poisonous to livestock that graze it. Although the toadflaxes may be slow to establish, once plants take root, control is very difficult since most herbicides are ineffective.
Where in the state is this plant found? The toadflaxes are most likely to be found along highways, railroad tracks and other transportation or communication lines, or anywhere livestock is brought into the state. Often the origins of an infested area can be traced back to an escape from an ornamental planting. Dalmatian toadflax has only been reported as small patches in a few counties, generally in the western part of North Dakota. However, yellow toadflax has been found in many counties across the state and is on the verge of becoming a major problem for land managers in North Dakota.
How do I control this plant? Prevention is the best method to keep Dalmatian
and yellow toadflax from invading North Dakota pasture, rangeland,
and wildlands. Herbicides can be effective but require repeated treatments
at high rates. The most commonly used herbicides are Tordon for both
yellow and Dalmatian toadflax, and Plateau or Telar for Dalmatian
toadflax control. Consult the latest edition of NDSU Extension Service
Circular W-253, the North Dakota Weed Control Guide, for recommended
use rates and locations. Biological control with insects or disease
organisms is in the research stage with limited releases in progress.
However, biological control is not recommended in North Dakota because
of the limited toadflax acreage. Also, the use of biological control
is likely to be very limited even if successful agents are found because
of the close relationship between these weedy species and the ornamental
varieties of snapdragon. Proper stocking rates to maintain competitive
forage species has helped reduce the spread of toadflax into grazing
lands. Burning is not effective because soil temperatures do not get
high enough to kill the roots. Burning may even have a detrimental
effect and cause an increase in the number of stems due to reduced
cover.
Photos 1, 2a, and 4 are courtesy of Dr. Steve Dewey, Utah State University, Logan, UT. Photo 3 is courtesy Celestine Duncan, Weed Management Services, Helena, MT. All other photos by Rodney G. Lym.
If you find this weed, report it to your local
weed officer.
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W-1239, December 2002
