In my previous blog I wrote that preventing the spread of invasive plants starts with identifying the plant. You need to know the enemy! The next challenge is how to get rid of it. In this blog I share different management strategies. These strategies are based on knowing something about the plant and its life story.
Management is often a long-term endeavor and may depend on how well-established the infestation is, whether other desirable plants need to be protected, what ecological services are provided by the invasive (e.g., erosion control, nesting sites, source of food) and, especially, understanding the plant’s life cycle.
Timing can be critical. Proper disposal of the plant material is important, too, as some plants can regrow from a small piece. Please think carefully about follow-up strategies. In some cases, you will need to be as persistent as the plant! Finally, always be looking for unwanted plants. The mantra in invasive species management is “early detection/rapid response.”
Here are some basic management principles with examples from where I live in New York, many of which are just as prevalent in Pennsylvania:
Prevent seed dispersal
- Garlic mustard flowers in early May and the seeds develop quickly. Before the seed pods ripen and open, by late June, cut the stalk down to the root and bag it for the trash.
- Japanese stiltgrass goes to seed in August/early September. Mow, cut or weed whack before then, but cutting too soon will allow another crop to germinate, mature, and set seed from the seed bank. Another approach is to cover it before it goes to seed and deprive it of sun. This works in the woods: during the growing season, temporarily cover areas of stiltgrass with black mulch fabric. Without sun, the grass dies within 2-3 weeks. Reuse the pieces of fabric (about 3′ x 5′) by moving it from one patch to another throughout the growing season or, on a semi-permanent basis, cover patches with newspaper (about 6 pages thick) or cardboard, weighted down with twigs and camouflaged with a handful of leaves or weeds. Sun and rain further obscure the newspaper. Leave the newspaper in place to decompose. Either way, planting some natives to compete with future stiltgrass seedlings should be part of the plan. Good choices (depending on whether you have shade or sun, dry or moist conditions) are Mayapple (Podophyllum peltatum) interplanted with native ginger (Asarum canadense), Senecio or Packera aurea (also called golden ragwort and groundsel), White wood aster (Eurybia divaricata), Christmas fern (Polystichum acrostichoides), and Marginal shield fern (Dryopteris marginalis). You could also try Hay-scented fern (Dennstaedtia punctiloba) but use with caution! (It is a very aggressive native and is not to be planted near formal gardens!) These may also work: Canada windflower (Anemone canadensis), Geranium maculatum combined with Sensitive fern, Northern wood oats (Chasmanthium latifolium), Sweet wood reed (Cinna arundinacea).
This link describes (under Controls) the covering and planting method for stiltgrass. Plan on a long-term commitment: http://www.nyis.info/index.php?action=invasive_detail&id=32
This link leads to an article on control of JSG in the home lawn and landscape: https://njaes.rutgers.edu/fs1237/
- Mile-a-minute vine produces bright blue berries as early as June. Remove the entire vine by pulling (wear gloves – it’s called “tear thumb” for a reason) and disposing in trash bags.
- Swallowwort vine – long string-bean type pods begin to open in mid-July, releasing wind-borne seeds.
Some invasive plants are best managed by persistent cutting
- Japanese Knotweed should be cut several times throughout the several growing seasons to exhaust the root system, the first cut when the plant reaches 2 or 3 feet tall and the last before the leaves turn color. Bag every piece and dispose with the trash.
- Mugwort can be cut every 2 weeks and left in place.
- Shrubs, such as Japanese barberry, multiflora rose, wine berry, oriental bittersweet and winged euonymus can be drastically cut but will often re-sprout. A watchful eye and persistence pays off.
Some invasives are best managed by digging out the root
- Swallowwort vine – Dig out the root at the crown.
- Others: Japanese barberry, multiflora rose, wine berry, oriental bittersweet and winged euonymus
Some invasive plants need selective use of herbicides for control
- Ailanthus, Japanese Angelica, and Glossy Buckthorn require painting the cut stem with a systemic herbicide or the plant will respond by forming thickets from root sprouts.
Some plants may be managed with this method:
Killing Buckthorn Without Chemicals: Buckthorn Baggie http://www.buckthornbaggie.com/baggie/
Some invasive plants need to be carefully disposed: These plants should not be added to your compost or brush pile because they can propagate from small fragments or bulbs: Japanese knotweed, Fig Buttercup, Goutweed, Spotted knapweed, Canada thistle, Cypress spurge, Leafy spurge, Garden loosestrife, and Star-of-Bethlehem.
- Porcelain berry: Hand pulling of vines in the fall or spring will prevent flower buds from forming the following season. Where feasible, plants should be pulled up by hand before fruiting to prevent the production and dispersal of seeds. If the plants are pulled while in fruit, the fruits should be bagged and disposed of in a landfill. For vines too large to pull out, cut them near the ground and either treat cut stems with systemic herbicide or repeat cutting of regrowth as needed.
- Viburnum Leaf Beetle: October to April, Cut and trash tips of twigs where eggs have been laid. http://www.hort.cornell.edu/vlb/manfaq.html
Each invasive species is different. Please use online resources to find up-to-date methods of control and disposal. Here is a good one: https://www.agriculture.nh.gov/publications-forms/documents/upland-invasive-species.pdf
The Pennsylvania Department of Conservation & Natural Resources maintains an invasive plants section on their website full of great useful information.
Managing invasive plants on your property helps to prevent the spread to the beautiful state parks and forests of Pennsylvania.
– Carolyn Reppert Sears, Ph.D.
Dr. Sears lives in NY but has strong familial ties to PA. Retired from a career teaching science, she co-directs The Invasives Project-Pound Ridge (NY), a volunteer effort to protect the natural beauty of Pound Ridge, preserve wildlife habitat, encourage the use of native plant species, and limit the spread of invasive species.
Featured photo: An invasive rogues’ gallery (Japanese knotweed, multiflora rose, mile-a-minute vine, swallowwort)