What Can I Do About Invasive Plants? The best insurance against future problems is to avoid the use of known invasive plants and educate others about the problems of invasive species. This website lists many of the plants that are considered invasive in Pennsylvania. Plants on this list should not be used around your home or community because they can escape cultivation and aggressively move into surrounding ecosystems. Avoid invasives by choosing plants that are native to your area. Natives often are adapted to a specific environmental niche, and have natural controls that keep them in balance. Minimize landscape disturbance. Invasive plants thrive on bare soil and disturbed ground where the native plant community has been displaced. The key to controlling invasives is to protect healthy native plant communities. Use fertilizers wisely. Proper site preparation begins with a soil test before applying fertilizer. High nitrogen levels sometimes give an advantage to invasive species that are better adapted to using plentiful nutrients for explosive growth. For soil fertility, try using organic, slow-decomposing compost and mulches Have a land management plan for maintenance over time. It makes sense when designing a property to plan for future maintenance. Lawns are maintained by weekly mowing, while gardens are often hand-weeded. Meadows in Pennsylvania may need to be mowed every year. Woodlands are probably the lowest-maintenance landscape, but they too will need to be monitored and invasive plants removed. Scout your property annually for invasives or other problems. The best way to control invasives is prevention, and prevention can only happen through vigilance. Listed on this web site are resources to help property owners. Remove invasives before they are a problem. Effective scouting or monitoring means that problems are found while they are still small and easily controllable. For instance, do not let invasive plants go to seed. Mechanical removal through digging or cutting is preferred. Large populations of invasives may need to be stopped chemically with spot applications of herbicide by trained individuals or by homeowners carefully following label instructions. Replace invasive plants with native or noninvasive species. Invasives are good at exploiting bare soil and empty niches. When you remove an invasive plant, unless there is another plant substituted, the invasive will tend to come right back. What grows in the future depends largely on what is there now; so it is important to fill that niche with a desirable plant that will provide seed for the future. Remove invasives as they appear while their densities are low. This gives the most immediate success because invasive plant control works best where there is a functioning native plant community still in place which can move right into the empty niche.
Characteristics of Invasive Plants Invasive plants are noted for their ability to grow and spread aggressively. Invasive plants can be trees, shrubs, vines, grasses, or flowers, and they can reproduce rapidly by roots, seeds, shoots, or all three. Invasive plants tend to: not be native to North America; spread rapidly, reproducing by roots or shoots; mature quickly; and if spread by seed, produce numerous seeds that disperse and sprout easily. Invasives are typically generalists that can grow in many different conditions and are exploiters and colonizers of disturbed ground. Impact of Invasive Plants Invasive species should not be used in our landscape because they are degrading our native plant communities and ecosystems. In fact, second only to habitat loss, invasives are a major factor in the decline of native plants. Plants like kudzu, purple loosestrife, and garlic mustard are displacing native plants and degrading habitat for native insects, birds, and animals. Endangered, rare, and threatened native species of plant and animals are especially at risk because they often occur in such small populations that make them particularly vulnerable. A very practical reason to avoid using invasive plants in your landscape is that they escape, spread and require regular weeding to manage even when grown in a cultivated yard. In urban and suburban areas the worst weeds are escaped ornamentals like Japanese honeysuckle, multiflora rose, Japanese knotweed, tree-of-heaven and oriental bittersweet. In yards, gardens, fields, and parks these plants are very expensive to control.
Norway maple, Acer platanoides, a common street and lawn tree that frequently excapes cultivation. Sycamore maple, Acer pseudoplatanus, a tall Eurasian tree invading urban and suburban woods in southern PA. Tree-of-heaven, Ailanthus altissima, grows throughout PA. Another immagrant from China introduced as an ornamental. Princess-tree, Empress-tree, Paulownia tomentosa, imported from China this purple-flowered tree has spread across southern PA by winged seeds. Siberian elm, Ulmus pumila, a fast growing tree reaching 50-70 feet high.
Common and Glossy buckthorns, Rhamnus cathartica and R. frangula (syn. Frangula alnus). Small trees or shrubs to 20' high with yellow sapwood and pink to orange heartwood. Japanese barberry, Berberis thunbergii, forms dense thickets in woodlands, wetlands and meadows. Shrub honeysuckles, five Lonicera species that rapidly invade and dominate field edges and pastures. Border privet, Ligustrum obtusifolium, imported from Japan, is the most common and invasive species of privet in southern PA. Common privet, Ligustum vulgare, is an aggressive thicket forming shrub imported from China and Europe. Guelder rose, Viburnum opulus, a tall shrub with maple-like leaves imported from Eurasia and escaped to woods fields and roadsides. Multiflora rose, Rosa multiflora, this import from Asia has become a noxious weed in PA field, pastures and woodlands. Russian olive & Autumn olive, Elaeagnus angustifolia and E. umbellata, imported from Asia, have become serious weeds in southern PA pastures and other open ground. Japanese spiraea, Spiraea japonica, was imported from Japan for its pink flowers. It escapes from cultivation to forest openings and meadows. Wineberry, Rubus phoenicolasius, imported from Asia for its raspberry-like fruit and now common on roadsides and in woods and thickets. Winged euonymus or Burning-bush, Euonymus alatus, a shrub from China and Japan imported for its bright purple-red fall color and frequently found along streams and in woods mostly in southern PA.
Five-leaf akebia, Akebia quinata, a woody twining vine from Asia that has escaped cultivation to disturbed woods in southeastern PA. Mile-a-minute weed, Polygonum perfoliatum, a slender annual vine with reflexed prickles was accidentally introduced from Asia with nursery stock and now a noxious weed in PA. Japanese honeysuckle, Lonicera japonica, a common ornamental vine from Asia now an abundant weed in roadside thickets, woods and fields across southern PA. Kudzu, Pueraria lobata, a vigorous half-woody vine introduced from Asia for ornament, forage and erosion control and now an uncommon but officially noxious weed in southeastern PA. Oriental bittersweet, Celastrus orbiculatus, a twining woody vine imported from Asia and rapidly replacing the native bittersweet in woods and fencerows. Porcelain-berry, Ampelopsis brevipedunculata, a deciduous, woody, perennial vine in the grape family imported from Asia.
Cheatgrass or Downy brome grass, Bromus tectorum, accidently introduced from Europe in ballast soil or impure wheat seed shipments. A serious agricultural weed in the midwest and western states. Common reed, Phragmites australis, a very large perennial grass, forms extensive colonies in wetlands. The scattered native American populations are being replaced by the vigorus European subspecies. Japanese stiltgrass, Microstegium vimineum, introduced from tropical Asia in packing material and spreading through moist areas open woods and clearings across southeastern PA and probably elsewhere.
Beefsteak Plant, Perilla frutescens, a member of the mint family introduced from India now occasionally found in moist shaded roadsides and woods. Canada thistle, Cirsium arvense, imported from Eurasia (not Canada) now common and noxious weed in fields pastures and roadsides throughout PA. Dame's-rocket, Hesperis matronalis, introduced from Europe to American gardens, now common in low woods floodplains and roadside ditches throughout PA. Garlic-mustard, Alliaria petiolata, a weed of shady moist spots in suburban gardens, woods and floodplains throughout PA; introduced from Europe. Giant hogweed, Heracleum mantegazzianum, 15 feet tall member of the carrot family introduced from Eurasia. Its sap can cause blisters so it is listed as a federal and PA noxious weed. Goutweed, Aegopodium podagraria, imported from Eurasia and frequently found in fields, thickets, woods and roadsides throughout PA. Japanese knotweed, Polygonum cuspidatum, an extremely difficult weed to control. Imported from Japan it dominates stream and river banks throughout PA. Lesser celandine, Ranunculus ficaria, an aggressive weed in wetlands imported from Eurasia Purple loosestrife, Lythrum salicaria, a European perennial with a woody base that has escaped gardens and destroyed large areas of waterfowl habitat by dominating wetlands and excluding all other plant life. Star-of-Bethlehem, Ornithogalum nutans and O. umbellatum, garden bulbs from Europe that escape to infest lawns and roadsides. Wild parsnip, Pastinaca sativa, a European import now a widespread and abundant weed of roadsides throughout PA.
Eurasian Water-milfoil, Myriophyllum spicatum, a common an abundant Eurasian invader of lakes and rivers throughout PA. Water-chestnut, Trapa natans, a locally abundant Eurasian invader of ponds and lakes.
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