In the News

Dalmatian Toadflax Tales of Woe
date posted: December 22 2005

Lake Tahoe Report #79
Aug. 10, 2004
By Susan Donaldson, Water Quality Education Specialist,University of Nevada Cooperative Extension

Many of us take great pride in our landscaping, spending happy spring and summer hours coaxing beautiful flowers in our garden beds. Perennials bring special satisfaction, as they grow back each year without replanting and often flower spectacularly. However, when the perennial is an invasive weed, our gardens can become a nightmare instead of a pleasure.

According to a recent study, there are now over 300 species of introduced, nonnative plants that are invading natural areas in the United States. More than half were intentionally introduced for use as ornamentals! Plants such as purple loosestrife, Scotch broom, and pampas grass seemed like perfect landscape accents. However, they turned into voracious, out of control invaders that have damaged ecosystems nationwide, displacing native plants and wildlife, using precious water supplies, and ruining recreational opportunities. In the Lake Tahoe Basin, the showy Dalmatian toadflax is beginning to expand rapidly and threatens to wreak havoc.

A snapdragon look-alike, Dalmatian toadflax (Linaria dalmatica) grows in bushy plants up to 3 feet tall, with heart-shaped leaves that clasp the stem. The flowers are bright yellow tinged with orange, and will “open their mouths” when pressed on the sides. Unlike snapdragons, the flowers have a long extension or spur growing from the lower lobe. Dalmatian toadflax is so attractive that it has been cultivated since the 16th century, and has spread throughout the world from its home range of the Mediterranean region. It was introduced into the western United States for use as an ornamental in 1874. A similar nonnative invasive plant, yellow toadflax, also called “butter and eggs” (Linaria vulgaris), is found in the basin as well, and can be distinguished from Dalmatian toadflax by its long, narrow leaves.

In June of this year, a huge infestation of Dalmatian toadflax was found stretching west from Foothill Road in Gardnerville across the Sierra toward Lake Tahoe. Where did it come from? Some 30 years ago, a Lake Tahoe resident moved to the Foothill Road area and transplanted three or four pretty, snapdragon-like plants from her garden to her new home. From this innocent garden activity, hundreds of plants have sprung up, and a major ecosystem disturbance is now threatening to spread into the Tahoe Basin.

The culprit? As you may have guessed, the homeowner was unknowingly transporting a noxious and invasive weed: Dalmatian toadflax. The Tahoe Basin Weed Coordinating Group continues to survey weeds basinwide. A number of infestations have already been found around the lake, most recently about 400 plants growing in Incline Village. So what is the big deal?

Dalmatian toadflax is a perennial, reproducing both from a large and vigorous root system and from seed. While the root system is impressive, it lacks the fibrous character of grasses, and fails to knit the soil together effectively. Areas with infestations by invasive, tap-rooted perennial weeds experience measurable increases in soil erosion. That, of course, is bad news for Lake Tahoe, where current efforts to protect lake clarity focus on erosion control.

Unfortunately, this weed is also very difficult to control. It grows back from root fragments left in the soil after pulling, requiring constant vigilance and years of follow-up efforts. Repeated rototilling (cultivation of the soil) can be successful in some cases, requiring eight to 10 cultivations per year for two or more years. However, this method is not desirable in the Tahoe Basin, where our goal is to stabilize soil and reduce erosion.

In many cases, chemical controls may be the best alternative. A research project is currently underway to test a new method of application in which clippers are dipped in herbicide and then used to lop off stems. The herbicide is sucked down into the root of the plant. By avoiding spray application, unwanted contamination does not occur. Results should be available by next year. In the meantime, call University of Nevada Cooperative Extension, (775) 784-4848, for advice on Dalmatian toadflax control, and do your best to avoid planting invasive plants!