By Norma Kline, OSU Extension Forester for Coos and Curry Counties

If you live near Bandon, you are likely very familiar with gorse (Ulex europaeus), an introduced exotic weed from Europe. Gorse is thorny and extremely painful to walk through, making areas of your property inaccessible. While gorse plants start out small, they can grow to over 10 feet tall with stout woody stems. These monoculture thickets suppress native vegetation (Figure 1). And even worse, gorse is extremely flammable, making it a severe fire hazard. In 1936, gorse growing in the empty lots between buildings in Bandon helped fuel a fire that caused significant destruction to the town.

While control of established mature gorse fields can be challenging, there are several approaches proven to be successful on the South Coast. The Gorse Action Groups (GAG) has a list of available gorse management strategies and recommended best management practices as well as a list of operators (see references). Mulching can be an effective approach, provided that the initial mulching work is followed-up by mowing, grazing or herbicide treatments. Mulching utilizes machinery to grind gorse, typically a skid steer with a mulching head or a rotary cutter on an excavator with a mulching head. The mulch is left in place to help suppress gorse seedlings. Eventually, the field of gorse can be transitioned to another use. When hiring a gorse contractor remember to check references and make sure that they are insured and have appropriate licenses. For example, a pesticide applicators license is needed if they are working with herbicides. See Hiring the Right Service Provider for your Family Forest: Chemical Applicator (see references).

Planting conifers to shade out the gorse plants can be a long- term solution. But reforesting in gorse infestations is not without challenges. After gorse has been initially treated, continued maintenance is required to prevent gorse from outcompeting and suppressing the conifer seedlings (Figure 2). Since seedlings can be susceptible to herbicide treatments; choosing the appropriate chemical and applying it in the correct time of year is important for success. Section M (Forestry and Hybrid Cottonwoods) of the PNW Weed Management Handbook is an excellent resource for landowners interested in brush control and site preparation on their woodland. Section M provides information regarding application timing and susceptibility of native conifers to various herbicides.  It’s important to remember that herbicides used on forest land must be specifically labeled for that use. Additionally, a notification of operations with the Oregon Department of Forestry is required for herbicide applications on forestland (see references).

Detecting and eradicating outlier gorse populations can help prevent gorse from expanding across the landscape. Even if you don’t have known gorse infestations in your area, you can help prevent the spread of gorse by monitoring your woodland. Monitoring and control of invasive species is a good practice to prevent small infestations from getting large and expensive to eradicate. Landowners can efficiently combine a number of monitoring tasks at the same time. For example, monitoring for invasive species and forest health issues as you drive your roads to check up on road conditions for preventative maintenance. Mark locations of invasive plants (or other issues) on a paper map or use a mapping app on your smart phone or tablet to drop digital “pins” on areas that need follow-up treatments. Developing a clear labeling strategy will help you keep track of any problems, for example the species and number of plants: Gorse-1, Gorse-5, etc. Most mobile mapping apps will allow you to label the digital pin. It’s a good idea to monitor your woodland at least annually, or more frequently If you have had recent projects using off-site machinery.

Natural enemies (biological controls) for gorse control are also being assessed. Effective biologic controls are safe and will not become problematic to crops or native plants. To date, several controls have been examined to determine effectiveness. These include the gorse seed weevil, gorse spider mite and gorse thrips. The spider mite had low impact for gorse control because it was affected by a predatory insect. The seed weevil was found to reduce seed production by 50% and may help gorse from spreading over the long term. Gorse thrips was first released in Oregon in 2020 and is still being monitored. Thrips feed on plant cells, targeting new growth and reduce flowering. More information on biocontrols can be found in the reference section.

Preventing gorse from becoming established on your woodland will save you considerable time and money. It’s a good idea to require contractors to pressure wash machinery prior to moving onto your property. While they will likely charge an extra fee for this, it is well worth it in the long term. Pay attention to your own vehicles, or even bicycle tires and footwear if you have traveled in gorse infested areas. Gorse seed are tiny, and easily transferred from one location to another.

References

Gorse Action Group: https://gorseactiongroup.org/

Section M (Forestry and Hybrid Cottonwoods) of the PNW Weed Management Handbook https://pnwhandbooks.org/sites/pnwhandbooks/files/weed/chapterpdf/forestry-hybrid-cottonwoods.pdf

Hiring the Right Service Provider for your Family Forest: Chemical Applicator: https://catalog.extension.oregonstate.edu/em9171

Oregon Forest Practice Rules: Chemical application https://www.oregon.gov/odf/working/pages/fpa.aspx E-Notification:https://www.oregon.gov/odf/working/pages/enotification.aspx

Biocontrols: https://solvepestproblems.oregonstate.edu/weeds/gorse https://www.oregon.gov/ODA/programs/Weeds/Pages/BiologicalControl.aspx