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Management Of Yellow Toadflax
Similar to Dalmatian toadflax, yellow toadflax is a deep-rooted perennial, which is difficult to control. One distinguishing characteristic between the two toadflaxes is the leaf. Yellow toadflax's leaf is narrow versus the broad-based, clasping leaves of Dalmatian toadflax. When flowering, the difference can easily be detected by yellow toadflax's orange-throated flowers versus the entirely yellow flowers of Dalmatian toadflax.
Mechanical Control
Handpulling for perennial weed control is rarely effective. However, handpulling may control this weed if populations are small and the plants are pulled consistently for five to six years. The site must be visited for 10 to 15 years to remove seedlings produced from dormant seeds.
Mowing is not recommended since it does not affect root reserves or buried seeds, nor is it feasible on rocky or steep slopes. Hand removal of the flowering tops from the plants is a marginal strategy even for very small infestations. Although removal prevents seasonal seed production and can prevent establishment of new infestations from seed, flowers must be eliminated every year for many years if this strategy is used.
Cultivation, where feasible, will control yellow toadflax. Sweep-type cultivators appear to work best, and cultivation should start early in June and be repeated every seven to 10 days. Eradication requires at least two years of cultivation, with four or five cultivations the second year.
Chemical Control
In Colorado, best results have been shown by applying herbicide just after a killing frost in the fall or during flowering when the plant reserves are low. Picloram (Tordon) applied at 2 quarts/acre (1.0 lb. ai/A) has been shown to provide the most control. The frost assists in breaking up the cuticle of the leaves and allows greater penetration of the herbicide. Soil type is an important factor determining the success of this herbicide, since leaching of the herbicide below the plant root zone is more likely on sites with sandy soils or on soils low in organic matter. Under dry conditions, picloram is not moved into the soil and significant loss of the chemical can occur in sunlight in three or four weeks. These herbicides can be purchased at an agricultural products supplier (please check the yellow pages for specific stores).
Biological Control
A defoliating moth, Calophasia lunula, has been tested for host specificity and intentionally released against Dalmatian and yellow toadflax in North America. Two other species, an ovary-feeding beetle (Brachypterolus pulicarius) and two seed capsule-feeding weevils (Gymnaetron antirrhini and G. netum) also have been shown to feed on both yellow and Dalmatian toadflax. Although each species has some degree of impact on individual plants or on seed production, it is too soon to tell if they will have enough of an impact to control this weed. If using biological control for toadflax, integrating another method of control is recommended.
Cultural Control
Maintaining healthy pastures with vigorous perennial grass stands is the best cultural control method for yellow toadflax. Competitive plants reduce the chance of toadflax seedling establishment since toadflax seedlings are poor competitors for soil moisture. Overgrazing in the spring by livestock can be detrimental to desirable species and increases the competitive advantage of toadflax, especially in spring when soil moisture is plentiful. Minimizing soil disturbance and preventing overgrazing are two important approaches to maintaining a closed community of desirable species.
Resources
Lajeunesse, S., P.K. Fay, D. Cooksey, J.R. Lacey, R.M. Nowierski, and D. Zamora. "Dalmatian and Yellow Toadflax: Weeds of Pasture and Rangeland."