Suppression

Suppression is the periodic control or elimination of a population of exotics within a generally infested area. Suppression offers only a temporary solution to the exotic problem, and generally must be repeated at regular intervals. It generally becomes a permanent maintenance project unless biological control can be established. (ESAFE 5955)

Current treatment options for specific areas usually involve herbicides, prescribed fire, grazing, and mechanical or manual removal. Fire, grazing, and mechanical cutting treatments usually control only the aboveground plant parts, reducing their height but suppressing the plants only temporarily. Manual treatment usually involves grubbing or pulling plants. This is very labor intensive and is practical only where plants and infestations are small. Thus manual treatment has limited but effective application in special habitats, such as recreational trails or nature preserves, and as a rapid means of first-sight elimination. Mowers, chain saws, and brush cutters remove aboveground plant parts, while leaving roots and rhizomes. Tree shears, root rakes, and harrows can cut and dislodge woody and rhizomatous plants, but leave soil bare for probable reinvasion and possible erosion if it is not rapidly stabilized with native plants. Nonetheless, these soil-disturbing techniques can start reclamation programs when multispecies infestations of invasive woody plants are encountered. (SFS-Britton)

Herbicide treatments often can be more easily and effectively applied following these other treatments. Herbicide treatments also minimize soil disturbance and leave the soil seed bank in place to reestablish native plants. Carefully planned and executed herbicide applications can specifically target nonnative plants and minimize impacts to native plants (Miller 2003) (http://www.invasive.org/weeds.cfm and  http://www.srs.fs.usda.gov/pubs/gtr/gtr_srs062). Well-developed applicator-directed techniques for selective control of nonnative trees and shrubs are tree injection and girdle treatments, basal sprays and wipes, cut-stem applications, and foliar-directed sprays (U.S. Department of Agriculture, Forest Service 1994). Directed treatments of nonnative vines and forbs usually involve foliar sprays applied with backpack sprayers. For treating extensive inaccessible infestations, broadcast applications of sprays and pellets using helicopter and tractor-mounted systems may be required. Yet even in broadcast treatments, the use of carefully timed selective herbicides can safeguard native plants. If the treatment is to be safe and effective, herbicide applicators must read, understand, and follow the herbicide label and its prohibitions before and during use. Continued surveillance and followup treatments are often required to control nonnative plant infestations. (SFS-Britton)