It has such an appealing appearance — radiant yellow flowers on a long stalk and a long bloom period. It looks like a three-foot-tall snapdragon on steroids, BUT, do not be sucked in. For under the ground are the most pernicious, aggressive tap and horizontal, perennial creeping roots you have ever tried to dig out.

Dalmatian toadflax (Linaria dalmatica ) is listed by the Washington State Noxious Weed Control Board as a weed that needs to be mandatorily controlled. It has run over pasture land and might be harmful to livestock.

This invader came from the Balkans, probably in animal feed or in treasured garden seed brought to new homes by immigrants.

I have seen it growing in the Balkans. There, it is well behaved and mixed in with other native plants. Unfortunately, it has claimed a boothold here in open lands with no real competition except from grasses struggling in over-grazed soil. And its natural predators are not native here.

It was first seen in Washington state in the mid-1920s.

The reason that this plant’s spread must be controlled is that it damages rangeland and pastures. The plant out-competes native grasses.

A single plant can produce 500,000 seeds; its roots can be 6 feet deep and up to 10 feet wide. This growth habit influences the means of eradicating the plant.

Mowing a field with Dalmatian toadflax can actually do more harm than good. Mowing can be a temporary control measure to prevent seed production, but will have to be repeated as new stems begin to flower, and it will not kill the plants.

Mowing machinery can actually spread the plant to other fields because seeds can stick to various parts of a tractor.

The plant can be killed with selected herbicides applied at the correct time of year, in the correct weather conditions.

As always, if you select to deal with this weed with an herbicide listed to control this weed, be sure to follow application directions precisely.

The Chelan County Noxious Weed Board (667-6669 or julie.sanderson@co.chelan.wa.us) and the Douglas County Weed Task Force (745-8531) can provide information on what types of herbicide to apply.

One of the most effective means of controlling this weed is the release of toadflax stem weevils. The adult insects eat the leaves and flowers and the larvae kill the stems by eating out the center. The weevils are approved for use on toadflax because this insect eats only toadflax and will not attack other plants.

If you have a large acreage infested with toadflax, contact Dale Whaley at the Douglas County Extension for more information and support for your eradication efforts. Dale can be reached by phone at 745-8531 or by email at dwhaley@wsu.edu.

 

A WSU Master Gardeners of Chelan County column appears weekly in The Wenatchee World. Bonnie Orr is one of three columnists featured.