Rodney G. Lym, NDSU Department of Plant Sciences
Once an area becomes infested, both species can dramatically reduce forage production and decrease native plant and wildlife habitat.
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Figure 1. Dalmatian (left) and yellow toadflax (right) plants look similar from a distance.
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.
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(Photo courtesy of Steve Dewey) 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. |
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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 3. Dalmatian toadflax (left) has broad heart-shaped leaves, while yellow toadflax leaves (right) are long and narrow similar to leafy spurge.
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.
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.
Yellow and orange
flowers are similar
to the domestic smapdragon and contain a long pointed spur. The
flowers are usually yellow and have orange centers. Dalmatian toadflax
is a perennial. Seeds are transmitted by the winds and the plant
depends on insects to pollinate it.
(Photo courtesy of Steve Dewey)
Dalmatian Toadflax
(Photo courtesy of Celestoue Duncan)
Dalmatian toadflax buds developing near the apex of the stem. The flowers grow closer to the top of the plant.
Dalmatian toadflax leaves
are broad and heart-shaped and get broader at the base as you move down
the stem. They range from one to three inches long.
(Photo courtesy of Steve Dewey)
Both competitor's root systems can reach a depth of six feet or more, while lateral roots (rhizomes) can extend 10 feet from the parent plant.
(Photo courtesy of Steve
Dewey)
(Photo courtesy of Steve Dewey)
These are rhizomes of Yellow Toadflax.
The fruit is egg shaped or it may look similar to a circle figure. The seeds can remain dormant in the soil up to 10 years before they sprout; it can take that long for the seed coat to fall off. Getting rid of the seed is not the answer for this menessing weed, due to the extensive root system and longevity of the seeds themselves, Dalmatian and Yellow toadflax have become a very serious problem.
(Photo courtesy of Steve Dewey)
When the fruit begins to die, a seed replaces it. It has 2 capsules which contain 100-200 seeds. A single plant may produce several hundred thousand seeds.
Mechanical control such
as hand pulling or grubbing
can be effective for small infestations.
There has been some evidence that grazing will reduce the spread, but it it is important overall to maintain a vigorous, competitive plant community that would reduce the chance of toadflax seedling establishment. Top
(Photo courtesy of Rod
Lym)
Yellow toadflax was introduced from Europe as an ornamental and often can be located in flower gardens, but it is now a serious problem to rangeland, roadsides, and waste areas. .
(Photo courtesy of Steve Dewey)
Not only does the yellow toadflax replace desirable grasses in rangeland and other land of high value, but it can lead to serious erosion problems.
Yellow toadflax is a perennial reproducing from seed as well as from underground root stalks. The yellow toadflax seed have no dormancy period, thus can germinate as soon as they are dropped, or can remain viable up to three years in the soil. The seeds develop in globe shaped capsule with notched, papery collars that act as wings which help in the distribution of the seeds.
Yellow toadflax can start to grow as early as April, giving the plant a long growing season to do plenty of damage to the land.
If you find this weed, report it to
your local weed officer.
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