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October 30, 2017
Mile-a-minute (Persicaria perfoliata), oriental bittersweet (Celastrus orbiculatus), and Japanese stiltgrass (Microstegium vimineum) swallowing up a pine in York County, PA. You could be next! Photo by Ryan Davis
Invasive plants have a lot in common with zombies. They’re dangerous, hard to dispatch, and have a tendency to surround and overwhelm even the most prudent landowner. Sometimes slowly, sometimes alarmingly fast, they will take over every inch of a property if left alone. Invasive plants are also specialists at “returning from the dead”. Simply cutting them is rarely enough to kill most invasives, and proper disposal of pulled or cut plants is paramount. Many landowners have inadvertently spread invasive plants by trying to remove them, only making their infestation much worse. If you want to remove invasive plants from your property (and you absolutely should), you’ll need to take utmost care to prevent them from coming back even stronger.
The best control technique when an invasive plant is still a seedling is typically hand-pulling; removing the entire root at this stage is easy. As they grow larger, many species become more difficult to control this way because pieces of roots will readily break off and sprout a new plant. Cutting or mowing invasives can be effective if you are very persistent and carefully monitor the area for new root sprouts. It takes several years, but you can kill many invasive species by cutting them close to the ground multiple times each growing season.
Application of a systemic herbicide (like glyphosate or tryclopyr) is recommended to control most invasives. These chemicals are absorbed by leaf or stem material and travel to the roots to kill the plant. If the application is fully effective the plant won’t resprout, but many invasive plants are so tough that repeated treatments are necessary. Herbicide can be applied to the bark, to cut stems, or sprayed on leaves. The method you use should be chosen based on how precisely you want to target plants that will die and how severe the infestation is. If invasives are intermixed with desirable native plants, a basal bark, cut stem, or hack-and-squirt method are best. If you are working on controlling a thicket, especially of plants like multiflora rose that are difficult to cut when large, a foliar application may be best.
Any treatment regime should be tailored to the species you are targeting. Find state-specific technical resources and contact information for professional guidance at Forests for the Bay. There you can explore a wealth of resources, including my favorite, the Pennsylvania Department of Conservation and Natural Resources fact sheets on invasive plant identification and management.
Many plants can sprout vegetatively, meaning they will start a new plant from a piece of stem, root, or leaf. Invasive plants are often experts at spreading this way. Many will survive being cut or dug up, and if they are just thrown in a compost heap or left on the ground, they will develop roots where they are disposed and keep growing. Be sure to completely kill a cut invasive plant before disposing it. You can solarize cut invasives by placing them into thick contractor bags and leaving them in the sun for a few weeks. Burning cut material is also a common technique, but be wary of species with light seeds that may rise from the heat of the fire only to disperse elsewhere, and be careful not to drop any stems when transporting them to the burn pile.
Cut stem herbicide treatment for burning bush, Euonymus alatus. Photo by Ryan Davis
Seeds of invasive plants are also often very hardy and stay viable in the soil for many years. The best approach is to remove invasive plants before they go to seed; otherwise you may inadvertently spread them during disposal. If an invasive has already gone to seed, do not remove them from the site, but bag or burn them there to ensure that they don’t get spread further. The University of New Hampshire Cooperative Extension guide to disposing non-native invasive plants covers species-specific disposal recommendations, before and after seeding, for most of the invasive plants we see in the Chesapeake Bay Watershed.
While they both “return from the dead”, I think that invasive plants are far scarier than zombies. Invasive plants are all too real; they have reduced the health of many of our natural landscapes, drive native species declines, and pose a serious threat to forest regeneration across the mid-Atlantic. Personally, I have scars from particularly bad run-ins with invasive plants, and some of my favorite wildlife species are severely impacted by habitat loss due to invasive incursion. I have cut invasive shrubs over and over only to see them spring back the next month, seemingly from the dead. With proper management and disposal, invasives can be removed and replaced with the native species that keep our ecosystems intact. All it takes is a little knowledge and a lot of hard work!
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