The Colorado Noxious Weed Act was originally passed in 1990 to empower local governments to implement management programs to protect and reclaim lands severely impacted by non-native, invasive plants. The weeds have been categorized in “A”,”B”, and “C” lists by their level of “noxiousness!” “A” List plants are designated for elimination. “B” List plants are ones whose spread should be stopped and List “C” plants should be controlled. Full lists can be found on the Colorado Weed Management website, cwma.org.
Noxious weeds can appear quite beautiful but they can threaten drinking water, agricultural crops, pastures and our native habitat. These plants have been transported to our state in various ways and some are even sold in other areas as nursery stock. They thrive because they have little natural control and have enormous root systems and seed banks.
One of the “B” List weeds in our area requiring attention is the Dalmatian Toadflax (Linaria dalmatica and Linaria genistifolia). It is a creeping perennial, part of the Figwort family (Scrophulariaceae). It grows from 2-4 feet tall, has yellow snapdragon-shaped flowers, sometimes presenting orange centers. A key to identifying Dalmatian Toadflax is by its waxy, dense, heart-shaped leaves. It is well adapted to more arid sites and can spread very effectively once established. A mature plant can produce up to 500,000 seeds annually and remain viable in the soil for up to ten years!
Because of its adaptability to our arid climate, it’s quite difficult to manage. It is best to get to it as soon as it’s detected. Depending on temperature, you may see it first emerge mid-May and flowering Mid-May through August but more likely it will be June and July in our high altitudes. The seeds mature July through September.
An integrated management is usually the best approach. If you can catch it in small groups, dig up and bag the entire plant for disposal. For larger infestation, digging just spreads seeds and it’s difficult to get all the roots. The key to deter a creeping perennial is to exhaust the nutrient stores in their root system. For an extensive discussion on what has been accomplished with mowing, biological and chemical control, please see CSU Fact Sheet 3.114 (http://www.ext.colostate.edu/pubs/natres/03114.html).
Once it’s under control, you will want to re-vegetate. Native seeds and plants like Golden Banner (a native which looks similar) and Columbine are good substitutes. OK, Noxious Weed Soldiers, it’s time to do your part to keep this plant under control!