Biodiversity

Invasive Species

NON-NATIVE INVASIVE SPECIES

Hundreds of species of non-native plants, animals, and fungi have been intentionally or unintentionally introduced into Delaware since the first arrival of European settlers in the 1600’s. These plants and animals were introduced for agricultural, horticultural, wildlife management and other reasons. Others were accidentally introduced. Some of these non-native species have responded to Delaware’s environment with great vigor, spreading aggressively into many natural habitats out competing native species. In addition, these foreign species had very few predators to keep their populations in check.

These invasions continue to occur and many of our worst non-native species have been introduced in the past 75 years. Plants like Callery (e.g., Bradford) pear, multiflora rose, autumn olive, bush honeysuckle, Japanese honeysuckle, oriental bittersweet, porcelainberry, mile-a-minute, English ivy, phragmites, and many other plants , can and do interrupt natural plant succession by smothering native plants. Animals – such as snakeheads, blue catfish, flat-headed catfish, several species of mollusks, and insects like the gypsy moth and emerald ash borer – can have serious, even lethal effects on native species and their habitats.

To reduce these negative effects on natural plant and animal communities we must develop and implement major efforts of control. While eradication would be ideal, in practice it is very difficult to eliminate most specie, therefore the primary goal of most control projects is to reduce non-native populations to levels that have minimum impact on natural habitats and their processes.

Efforts to combat the spread of non-native species are underway in Delaware. Although funding is limited, state, county, and municipal governments, non- governmental organizations and private citizens continue to find new and more effective ways to control non-native intruders.

One recent control measure is the ban of the sale of many of the most disruptive of Delaware’s non-native invasive plants. This law, which went into effect in July of 2022, prohibits the sale of 37 species of non-native plants (see list). There is much more that can and should be done to control non-native invasive plants and animals in the First State.

INVASIVE PLANTS

The Delaware law, implemented on July 1, 2022, bans the propagation, sale, purchase, or transport of 37 invasive plant species. That list includes 10 species that prior to 2022 were still bought and sold in Delaware. Those 10 species are no longer in commerce in our state and include:

Norway maple (Acer platanoides).
European Privet (Ligustrum vulgare)
Japanese barberry (Berberis thunbergii)
Lesser periwinkle (Vinca minor)
Winged euonymus (Euonymus alatus)
Callery pear (Pyrus calleryana)
English ivy (Hedera helix)
Creeping Jenny (Lysimachia nummularia)
Japanese pachysandra (Pachysandra terminalis)
Chinese wisteria (Wisteria sinensis)

The following plants were either introduced accidentally or purposefully in the past but are no longer bought and sold. They remain a problem in managed and natural landscapes and should be removed whenever possible. Delaware agencies like the Department of Transportation and the Department of Natural Resources and Environmental Control have taken action to prioritize some parts of the state for the expensive and tedious task of removal. Consider taking action on your own property to remove these plants and volunteering in public lands. You will find more information on ways to get involved in the “Take Action” section of this website.

Multiflora rose (Rosa multiflora).
Japanese honeysuckle (Lonicera japonica)
Oriental bittersweet (Celastrus orbiculatus)
Japanese stilt grass (Microstegium vimineum)
Japanese knotweed (Fallopia japonica)
Autumn olive (Elaeagnus umbellata)
European reed (Phragmites australis subsp. australis)
Hydrilla (Hydrilla verticillata)
Morrow’s honeysuckle (Lonicera morrowii)
Mile-a-minute weed (Persicaria perfoliata)
Purple loosestrife (Lythrum salicaria)
Yam-leaved Clematis (Clematis terniflora).
European Sweetflag (Acorus calamus)
Wineberry (Rubus phoenicolasius)
Garlic mustard (Alliaria petiolata)
Porcelain berry (Ampelopsis glandulosa)
Marsh Dewflower (Murdannia keisak)
Lesser celandine (Ficaria verna)
Amur honeysuckle (Lonicera maackii)
Tartarian honeysuckle (Lonicera tatarica)
Tree of heaven (Ailanthus altissima)
Spotted knapweed (Centaurea stoebe subsp. micranthos)
Creeping water primrose (Ludwigia peploides subsp. glabrescens)
Water hyacinth (Eichhornia crassipes)
Parrot-feather (Myriophyllum aquaticum)
Orange daylily (Hemerocallis fulva)
Yellow flag iris (Iris pseudoacorus)

What we can do

Do not plant invasive non-native plants in the landscape.
Plant and maintain native plants in community and natural areas.
Develop and fund control programs that target the most disruptive non-native species on private and public lands.
Follow all laws, regulations and recommendations concerning invasive species.