A Comparison of Mechanical Versus Chemical Control of the Invasive Species Myrtle Spurge (Euphorbia myrsinites)

Abstract

Myrtle spurge (Euphorbia myrsinites) is an invasive plant in North America that was introduced from Eurasia as a drought-tolerant ornamental. It has escaped cultivation and is widespread in western North America. Infestations can be reduced by either mechanical or chemical means, but the two approaches have not been compared directly. One study recommended mechanical treatment in the spring and chemical treatment in the fall, but neither recommendation was supported by data. To test the effectiveness of mechanical versus chemical treatment in the fall, we located six sites in the foothills of the Wasatch Mountains in Utah that were uniformly infested with myrtle spurge. At each of the sites we randomly assigned a 2.25 m2 quadrat to one of three treatments (i.e., mechanical, chemical, or control). The mechanical treatment entailed hand pulling and the chemical treatment involved applying the herbicide Roundup to each myrtle spurge. The controls were unmanipulated. We photographed each quadrat pretreatment and one year post-treatment. Both mechanical and chemical approaches significantly reduced the percent cover and stalk count of myrtle spurge compared to the controls. Additionally, the effects of the two treatments did not differ from each other. These results indicate that land managers can control myrtle spurge in the fall with either treatment and do not have to wait until the spring to employ mechanical methods. Mechanical removal of myrtle spurge is better suited to events that involve members of the general public such as “Purge Your Spurge” activities because they reduce the public's exposure to herbicide.