- Pull seedlings and small or shallow-rooted plants when soil is moist. Dig out larger plants, including the root systems. Use a spading fork or weed wrench for trees or shrubs.
- To prevent spread of seeds of desirable ornamental plants, cut off spent flowers ("deadhead") or cut off seeds or fruits before they ripen. Bag, and burn or send to the landfill.
- Mow or cut back at least 3 times a season to deplete plants' store of nutrients, reduce seed formation, and kill or minimize spread of plants. If necessary, repeat each year.
- Controlled burning during the spring, repeated over several years, allows native vegetation to compete more effectively with the exotic. This may require a permit. Spot treatment with glyphosate in late fall can be used to make this method more effective.
- Use a corn-based pre-emergence herbicide on annual weeds. This product is also an organic fertilizer, i.e., it can stimulate growth of existing plants, including weeds, so it is appropriate for lawns and gardens but may not be appropriate in woodlands.
- In lawns, spot treat with broad-leaf weedkiller. Good lawn-care practices (test soil; use lime and fertilizer only when soil test shows a need; mow high and frequently; leave clippings on lawn) reduce weed infestations.
- Cut down the tree. Grind out the stump, or clip off re-growth.
- Girdle tree: cut through the bark and growing layer (cambium) all around the trunk, about 6" above the ground. Girdling is most effective in spring when the sap is rising, and from middle to late summer when the tree is sending down food to the roots. Clip off re-growth.
- Hack & squirt: Hack a hole (several holes in larger trees) downward into the growing layer, and squirt in glyphosate (or triclopyr if recommended in text below). Follow label directions for Injection and Frill Applications. This is most effective from middle to late summer. Clip off any re-growth or paint with glyphosate.
- Cut down, and paint the cut stem or stump with glyphosate (or triclopyr if specified below). Follow label directions for Cut Stump Application. Clip off re-growth or paint with glyphosate. See Note on Herbicides.
- Paint foliage with glyphosate herbicide (see Note on Herbicides). Use an envelope dauber (small sponge-topped bottle), following label directions for "wiper" method. Add a drop of food color for visibility, or use a foam spray. Avoid dripping on non-target plants, because glyphosate kills most plants except moss. If it rolls off waxy or grass-like foliage, use additional sticker-spreader. Deciduous trees, shrubs, and perennials move nutrients down to the roots in late summer, so glyphosate is particularly effective at this time as well as when flowering plants are in bloom. Several invasive exotics retain their foliage after native plants have lost theirs, and resume growth earlier in spring than most natives. This allows you to treat them without harming the natives. However, the plant must be growing for the herbicide to work, and more may be needed in cold weather because growth is slower.
NOTE ON HERBICIDES: Maryland Native Plant Society (MNPS) strongly recommends non-chemical methods of control wherever feasible. However, for large infestations, and for a few plants specified below, non-chemical methods are inadequate. Applied carefully to avoid non-target plants, glyphosate is the least environmentally damaging herbicide in most cases. Roundup contains a stronger concentration of glyphosate than Kleen-Up. Both contain a petroleum-based sticker-spreader. Rodeo, the glyphosate formulation for wetlands, does not contain any sticker-spreader and thus is safer for the environment. The smallest size of Rodeo available is one quart of concentrate, obtainable from farm supply stores for about $60 in 1999. Add food coloring for visibility, and a soap-based sticker such as Cide-Kick. For small applications, another choice is Roundup Sure Shot Foam, easier to see and control than liquid Roundup. Glyphosate is ineffective on some plants; for these, triclopyr (Garlon), a stump and brush killer, may be indicated. When using herbicides, read the entire label and observe all precautions listed, including proper disposal. If in doubt, call your state Extension Service.