Working together to strengthen and support noxious weed management efforts in Montana.

Linaria dalmatica

MSU July Weed Post – Weed Spread & Climate Change

Monday, July 14th, 2014


This month’s post comes to us from Dr. Lisa Rew, Associate Professor in the Department of Land Resources and Environmental Sciences at MSU, and highlights some of her recent work looking at weed spread along elevation gradients and how this may help us better predict patterns of invasion within the context of a changing climate. If you have any questions regarding her research, please contact Lisa directly at

Excerpt from this month’s weed post:

Whether we like it or not, our climate is changing: generally Montana is getting warmer and patterns of precipitation (amount, form -snow or rain, timing) have changed in various ways across the state.  In addition, the human population continues to grow in many parts of Montana, and this has increased the frequency and intensity of road and trail use. Understanding how weeds respond to such changes and where new populations are likely to occur is helpful for planning weed management at the broader scale. Dalmatian toadflax, originally from Eurasia, has been present in southwest Montana since the early to mid-1900s and occurs in a range of areas including our more mountainous areas. Weeds respond to disturbance and are more abundant on bareground than in healthy growing vegetation, which is why they are abundant along roadsides. So what is stopping the spread of this and other species to higher elevations and away from roads and trails? Are seeds not getting there? Is the climate so inclement that seeds arriving at higher elevations cannot germinate or establish? Or, does the intact high-elevation vegetation stop the invasion?

Finish reading the July 2014 MSU Weed Post.

Importance of Matching your Bug to Your Toadflax

Thursday, May 15th, 2014


It is critical that the appropriate stem-boring weevil be utilized on the specific species of toadflax you are trying to control. Presently, the only reliable way to distinguish Mecinus janthinus(for yellow toadfax) and M. janthiniformis (for Dalmatian toadflax) appears to be the host plant on which they were collected. Please discuss with your supplier to ensure the agents you receive were collected from the same species of toadflax for which you plan to release them. Morphological differences of the weevils are very subtle and may not be reliable.

Biological Control Agents

The stem-mining weevil Mecinus janthinus was released in the US and Canada as a biological control agent of Dalmatian and yellow toadflax. Recent research has shown that rather than a single Mecinus species, there are two host-specific Mecinus weevils that utilize weedy toadflaxes. These are:

• Mecinus janthinus, which utilizes yellow toadflax, and,

• Mecinus janthiniformis, which utilizes Dalmatian toadflax.

Both weevils have apparently been released and established in the U.S. Choosing the appropriate host-specific weevil should increase the efficacy of biological control of both Dalmatian and yellow toadflax.

Dalmatian and Yellow Toadflax (Linariadalmatica and L. vulgaris)Identification:

Dalmatian and yellow (or common) toadflax are members of the Plantaginaceae (plantain) family, and are easily recognized by their snapdragon-like yellow flowers (right) with a single long spur. Flowers can bloom from early summer until killing frost.

• Dalmatian toadflax ranges in height from 15-60 inches with broad, fleshy and heart-shaped leaves which clasp the stem.

• Yellow toadflax is shorter, from 7-32 Inches tall with leaves that are long, linear and noticeably less succulent

Visit the weed identification pages for yellow toadflax and dalmatian toadflax for more information on these two weeds.

Dalmatian toadflax is on the left and Yellow toadflax on the rigth

Dalmatian toadflax is on the left and Yellow toadflax on the right

Please contact your local county weed coordinator or Gary D. Adams, State Plant Health Director at USDA, APHIS, PPQ if you have questions.

Invasive plants in wildland ecosystems: merging the study of invasion processes, with management needs

Wednesday, July 17th, 2013


Introduction: Increasing numbers of non-native species threaten  the values of wildland ecosystems. As a result, interest in and  research on invasive plant species in wildland  settings has accelerated. Nonetheless, the ecological and economic impacts of non-native species continue to grow, raising the question of how to best apply science to the regulation and  management of invasive plants. A major constraint  to controlling the flow of poten­tially undesirable  plant  species is the lack of a strong  regulatory framework  concurrent  with increases in trade volume. To address this, ecologists have been developing models to predict which species will be harm­ful to wildland  values and are working with the horticultural industry  to apply this information to the sale of species. The management of established invasive plants is hampered  by conflicting goals, a lack of information on management outcomes, and a lack of funding. Ecologists and weed scientists can provide a scien­tific basis for prioritizing species for control and for managing species composition  through  the application of  control  technology,  which  can  take  place  simultaneously with  the  manipulation of  the  ecological processes that influence community susceptibility  to invasion. A stronger scientific basis for land management decisions is needed and  can be met through  nationally  funded  partnerships  between university and agency scientists and land managers.

Authors: Carla MD’Antonio, Nelroy  E Jackson, Carol  C Horvitz ,and Rob Hedberg

Download and read the complete Research Report on Invasive Plaints in Wildland Ecosystems..

Toadflax – MSU November Weed Post

Thursday, November 29th, 2012


This month MSU is  featuring Dalmatian and yellow toadflax, including information on their hybridization.  Didn’t know they could hybridize???  Well, then there is definitely something new for you in this month’s post from Montana State University.  Download the  November 2012 MSU Weed Post on toadflax.

Visit the MWCA Weed ID page for details about Dalmatian Toadflax and Yellow Toadflax.  Contact your local weed coordinator if you think you find it in your area.

MSU June Post – Biological Control

Saturday, June 30th, 2012


Biological control is a term often used to describe insects that help to control noxious weeds.   The June MSU Monthly Weed Post provides updated information about some of the agents currently available for leafy spurge, spotted knapweed, dalmatian toadflax and houndstonge.

Download the June 2012 Monthly Weed Post from Montana State University.

Visit the MWCA Biological Weed Control page for more information.  Contact your local weed coordinator for help getting biocontrol agents in your area.

Growth inhibition of Dalmatian toadflax, Linaria dalmatica (L.) Miller, in response to herbivory by the biological control agent Meeinus janthinus Germar

Tuesday, July 26th, 2011


Abstract:  Our study reports the results of field and garden experiments designed to quantitatively evaluate the impact of herbivory by a weed biological control agent, the stem-mining weevil Mecinus janthinus Germar, on the growth of its exotic host Dalmatian toadflax, Linaria dalmatica (L.) Miller. Herbivory by M. janthinus under both natural and manipulated environmental conditions inhibited L. dalmatica growth. Reductions in stem length, biomass, and growth were more pronounced for plants subjected to both exophagous (adult) and endophagous (larval) feeding injury than for plants exposed only to adult folivory. Decreases we observed in root biomass could additionally inhibit shoot production from lateral roots. This provides a plausible mechanism explaining anecdotal reports correlating the reduced spread of L. dalmatica with attack by M. janthinus. Our results indicate that L. dalmatica growth is compromised once a threshold density equivalent to 5 M. janthinus larvae per stem is exceeded. The consistency of growth responses observed in this study suggests that a mechanistic/quantitative approach, such as measuring the impact of M. janthinus herbivory on L. dalmatica, is a robust and relevant method for postrelease evaluations of weed biocontrol efficacy.

Authors: Schat, Marjolein; Sing, Sharlene E.; Peterson, Robert K. D.; Menalled, Fabian D.; Weaver, David K.

Download and read the complete report.

Assessing Environmental Risks for Established Invasive Weeds: Dalmatian (Linaria dalmatica) and Yellow (L. vulgaris) Toadflax in North America

Tuesday, July 26th, 2011


Abstract: Environmental risk assessments characterizing potential environmental impacts of exotic weeds are more abundant and comprehensive for potential or new invaders than for widespread and well-established species such as Dalmatian (Linaria dalmatica [L.] Mill.) and yellow (L. vulgaris Mill.) toadflax. Specific effects evaluated in our assessment of environmental risks posed by yellow and Dalmatian toadflax included competitive displacement of other plant species, reservoirs of plant disease, animal and insect use, animal toxicity, human toxicity and allergenicity, erosion, and wildfire. Effect and exposure uncertainties for potential impacts of toadflax on human and ecological receptors were rated. Using publicly available information we were able to characterize ecological and human health impacts associated with toadflax, and to identify specific data gaps contributing to a high uncertainty of risk. Evidence supporting perceived negative environmental impacts of invasive toadflax was scarce.

Authors: Sing, Sharlene E.; Peterson, Robert K. D.

Download and read the complete report.

Weed of the Week – Dalmatian Toadflax

Thursday, September 16th, 2010


Dalmatian toadflax was introduced into the west coast of the United States in the late 1800’s.  It was brought here from the Mediterranean region as an ornamental plant.  It has escaped captivity and now infests much of the northwestern United States.  Unfortunately, this weed is still sold in greenhouses as Wild Snapdragon, Butter and Eggs, or Jacob’s Ladder.  Dalmatian toadflax was first discovered in south-central Montana in the 1940’s.  This weed has been reported in 43 counties throughout the state.

Concerns Dalmatian toadflax is a great concern because it will displace native vegetation and consequently displace animals associated with native vegetation.  This weed is extremely successful at displacing native vegetation because it spreads both rhizomatously (roots that run parallel to the ground surface) and by seed.  One plant can produce 500,000 seed per year.  The loss of native vegetation will also increase soil erosion, sediment yield, and surface runoff due to loss of bunch grasses and sod-forming grasses.

Cattle ranchers are seeing lower carrying capacity on infested sites.  Land that has Dalmatian toadflax can have lower appraisal value because of the cost of controlling it and the negative impact the weed has on the land.

Identification Dalmatian toadflax is very similar in appearance to yellow toadflax.  The main difference between Dalmatian and yellow toadflax are the leaves.  The leaves of Dalmatian toadflax are heart shaped with smooth edges and are arranged alternately on the stem.  The leaves and stem are a whitish to bluish in color.  The flowers are very similar to yellow toadflax, they are bright yellow with an orange throat and look like a snapdragon flower.  Another distinction between yellow toadflax and Dalmatian toadflax is that the Dalmatian can grow up to 3 feet tall.

What can you do? The best strategy for managing toadflax infestations is an integrated approach that focuses on preventing seed formation and vegetative spread.  Having multiple approaches to toadflax is crucial because of the wide range of conditions it inhabits and due to its genetic variability.  Mechanical methods such as hand pulling and digging are effective in newly established, small patches.  Hand pulling toadflax works when the weed is young and the conditions are moist.  Mowing will not help reduce toadflax populations because it does not remove the root system.  Sheep will graze toadflax when it is in bloom but this is not enough to control an infestation.  There are a number of biocontrols being studied; one in particular has shown promising results.  This insect is mecinus janthinus and it is a stem boring weevil that causes wilt and suppressed flower production.  Herbicides are an effective method for control of toadflax.  Revegetation is a very important tool in managing toadflax.  Integrating some or all of the above-mentioned tools into a long-term management strategy will help control Dalmatian toadflax infestations.  If you have any questions about noxious weeds call the weed district.

Visit the MWCA Weed ID pages for additional information and pictures of dalmatian toadflax.

This series of articles was developed by Ravalli County.  If you would like to use these articles please contact Ravalli County Weed District Weed Coordinator at (406) 777-5842.