Biological control of invasive Linaria spp. in the Western United States

Authors: SING, SHARLENE - Us Forest Service (FS); TOSEVSKI, IVO - Commonwealth Agricultural Bureau International (CABI) - Switzerland; WARD, SARAH - Montana State University; WEAVER, DAVID - Montana State University; Gaffke, Alexander

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 5/30/2022
Publication Date: 6/1/2022
Citation: Sing, S.E., Tosevski, I., Ward, S.M., Weaver, D.K., Gaffke, A.M. 2022. Biological control of invasive Linaria spp. in the Western United States. Book Chapter. 294-311.

Interpretive Summary: Since its introduction to the United States, yellow and common toadflax has been a problematic invasive weed that has negatively impacted crops and rangeland. Multiple biocontrol agents introduced to help control these invasive weeds vary in efficiency of control of these weeds. A scientist at the USDA, ARS, Center for Medical Agricultural and Veterinary Entomology, Gainesville, Florida, in collaboration with university, federal, and international colleagues, have reviewed the success and failures of the toadflax biocontrol. This review provides critical insight into the biocontrol programs and agents and outlines specific actions to improve effective control of this weed in the future, resulting in cost savings for agricultural produce.

Technical Abstract: Anecdotal reports indicate that invasive yellow or common toadflax (Linaria vulgaris), and Dalmatian toadflax (L. dalmatica) were first deliberately introduced to North America for ornamental purposes, and later accidentally as a seed contaminant. In the absence of laws specifically regulating the importation of exotic plants (as opposed to plant pests) into the United States, colonial and other early immigrant plant lovers ranging from homesteaders to miners to horticultural enthusiasts were unconstrained in importing and sharing non-native flora, including toadflax. The widespread distribution of both species likely resulted in novel hybridization events of these species in North American, resulting in the establishment of a third, even more invasive toadflax. Most unintentionally introduced toadflax-feeding insect species and approved toadflax biocontrol agents were initially thought to accept both yellow and Dalmatian toadflax hosts, with host preference often evident following establishment in North America. In response, concerted effort was repeatedly made to find, evaluate, and release additional host races or biotypes of previously approved toadflax biocontrol agents. Molecular diagnostics confirming the introduction of cryptic species have also explained localized issues of establishment and efficacy associated with agents presumed to attack both L. dalmatica and L. vulgaris. The earliest introduced toadflax specialist herbivores, flower or seed feeding beetles and a defoliating moth provide minimal control of toadflax. However, the established stem mining and stem galling biocontrol agents have resulted in widespread suppression and control of toadflax, resulting in significant cost saving and environmental protection.