Invasive Species: Delaware's Unwanted Green Invaders (2024)

Hundreds of species of non-native plants have been introduced to Delaware since the arrival of European settlers in the 1600s. Many of these species have thrived in the state's environment, outcompeting native plants and spreading aggressively. Some of the most common invasive plant species in Delaware include Japanese honeysuckle, English ivy, and multiflora rose, which can smother native plants and disrupt natural plant succession. To combat the negative effects of these invasive species, Delaware has implemented control measures such as banning the sale of certain invasive plants and developing programs to target and control disruptive non-native species.

Invasive species in Delaware

Delaware has a variety of invasive plant species that are harmful to the local environment. These non-native plants can overpopulate areas and are detrimental to native species and local ecosystems.

The Delaware Invasive Species Council (DISC) defines an invasive plant as any "living part, cultivar, variety, species, or subspecies not native to Delaware" that has the potential to result in "widespread dispersal and establishment", can "out-compete other species in the same area", exhibit "rapid growth or high seed or propagule productions", and become "established in natural areas in the State".

Some of the most common invasive plant species in Delaware include porcelain berry, Asiatic bittersweet, Japanese honeysuckle, and Mile-a-minute weed. Porcelain berry, native to northern China and Japan, is a perennial vine that grows quickly, smothering and eventually killing native plants due to its large leaves and fast growth. Asiatic bittersweet and Japanese honeysuckle are also vine species that grow up native plants and smother them. Mile-a-minute weed is an annual that grows from seed every spring, slowly at first, and then rapidly overtaking small trees.

Another highly invasive plant is the Callery or Bradford pear, which is native to China and Vietnam and is known for its white flowers. This tree has been an issue in the state for some time, and a ban on its sale, along with many other invasive species, went into effect on July 1, 2022. Norway maples are also invasive in Delaware, as they grow faster than native maples, create dense shade, and have a shallow root system that makes it difficult for native seedlings to thrive.

In addition to these, some invasive shrubs in the area include the burning bush, Japanese barberry, and multiflora rose. The burning bush, native to central and northern China, Japan, and Korea, aggressively outcompetes native species and quickly reproduces from its fallen berries. Japanese barberry, also native to Japan and eastern Asia, often provides a habitat for ticks carrying Lyme disease bacteria. The multiflora rose, native to eastern Asia, China, Japan, and Korea, has been causing problems since the 1980s with its quick growth and spread due to birds dispersing its seeds. This plant creates dense thickets that exclude native herbs and shrubs from taking root and can be detrimental to the nesting of native birds.

To protect Delaware's ecosystems, the state has implemented measures such as the Invasive Plant List and the Plant Watch List, prohibiting the sale and distribution of invasive plant species, and promoting the planting of native species instead.

Non-native plants in Delaware

In Delaware, there are a number of invasive plant species that have been identified by the Delaware Invasive Species Council (DISC) and the Delaware Department of Agriculture. These include:

• Amur honeysuckle (Lonicera maackii)
• Autumn olive (Elaeagnus umbellate)
• Callery pear or Bradford pear (Pyrus calleryana)
• Chinese wisteria (Wisteria sinensis)
• Creeping Jenny (Lysimachia nummularia)
• Creeping water primrose (Ludwigia peploides subsp. glabrescens)
• English ivy (Hedera helix)
• European privet (Ligustrum vulgare)
• European reed (Phragmites australis subsp. australis)
• European sweetflag (Acorus calamus)
• Garlic mustard (Alliaria petiolata)
• Hydrilla (Hydrilla verticillata)
• Japanese barberry (Berberis thunbergii)
• Japanese honeysuckle (Lonicera japonica)
• Japanese knotweed (Fallopia japonica)
• Japanese pachysandra (Pachysandra terminalis)
• Japanese stiltgrass (Microstegium vimineum )
• Lesser celandine (Ficaria verna)
• Lesser periwinkle (Vinca minor)
• Marsh dewflower (Murdannia keisak)
• Mile-a-minute weed (Persicaria perfoliata)
• Morrow's honeysuckle (Lonicera morrowii)
• Multiflora rose (Rosa multiflora)

In addition to the above-mentioned plants, there are also several other invasive species in Delaware, such as the porcelain berry, Asiatic bittersweet, and Norway maple. These plants can cause significant damage to native ecosystems and it is important for residents to be aware of them and take steps to prevent their spread.

To address the issue of invasive plant species, Delaware has implemented regulations and restrictions on the import, export, sale, and propagation of these plants. The state also encourages the preservation and cultivation of native plant species, which can help restore local ecosystems and provide a more suitable habitat for native wildlife.

Invasive plant laws in Delaware

Delaware has strict laws in place to combat the threat of invasive plant species. The state's legislation defines an "invasive plant" as any living part, cultivar, variety, species, or subspecies not native to Delaware that has the potential to result in widespread dispersal, outcompete other species, exhibit rapid growth, and become established in natural areas within the state.

The laws, outlined in Chapter 29 of the Delaware Code, specifically prohibit the import, export, sale, transport, distribution, or propagation of any plant identified as invasive by the Secretary of the Delaware Department of Agriculture, in coordination with the Native Species Commission. This includes any living part or seed of the plant. The Secretary maintains an "Invasive Plant List," which includes species such as Amur honeysuckle, Japanese knotweed, and English ivy, among others.

The legislation also addresses potentially invasive plants, which are those that have the potential to become invasive but are not yet widespread. Plants identified as potentially invasive must be sold with a tag or label that clearly identifies them as such. The Secretary maintains a "Plant Watch List" for these species.

Violations of the invasive plant laws in Delaware carry civil penalties ranging from $50 to $500 for each occurrence. However, before imposing a penalty, the Secretary must offer advice on compliance and an administrative hearing. Individuals who violate the law have the right to appear personally, be represented by counsel, and submit evidence and witnesses in their defense.

The laws aim to protect Delaware's unique natural environment and ecosystems by reducing the sale and distribution of invasive species, which can cause significant environmental and economic harm. The legislation also encourages the use of native plants, which provide food and habitat for birds and other wildlife, improve water management, and offer economic benefits to businesses and residences.

The Delaware Invasive Species Council (DISC) also plays a crucial role in identifying and assessing invasive plant species in the state. They have developed a comprehensive list of invasive and potentially invasive plants based on expert assessments and environmental evaluations.

Invasive plant control in Delaware

Invasive plant species in Delaware are a growing concern, with new problem plants emerging regularly. The Delaware Invasive Species Council (DISC) defines an invasive plant as any "living part, cultivar, variety, species, or subspecies not native to Delaware" that has the potential to exhibit specific characteristics, including rapid growth, outcompeting native species, and widespread dispersal. These plants can cause significant harm to local ecosystems and native species, and their control and management are crucial for preserving the state's natural environments.

Identification of Invasive Plants

The Delaware Department of Agriculture maintains an Invasive Plant List and a Plant Watch List to identify and monitor invasive plant species. The Invasive Plant List includes species known to be invasive, such as Amur honeysuckle, Autumn olive, Callery pear, and Japanese honeysuckle. The Plant Watch List contains plants with the potential to become invasive, such as Thunberg's bushcover and Lespedeza thunbergii. These lists are regularly updated and revised to reflect the changing nature of invasive plant species in the state.

Control and Management Strategies

To address the issue of invasive plants, Delaware has implemented several measures. Firstly, there are restrictions on the import, export, sale, transport, and propagation of plants on the Invasive Plant List, unless prior written approval is obtained from the Secretary of the Delaware Department of Agriculture for research, education, or control purposes. This helps prevent the introduction and spread of invasive species.

Secondly, the state encourages the preservation and planting of native species, which can help combat the damage caused by invasive plants and promote the growth of local ecosystems. Native plants such as red maple, oak tree species, birch, hickory, and native azaleas are recommended for gardens and landscapes.

Public Awareness and Education

Educating the public about invasive plant species is crucial for early detection and prevention. Organizations like the Delaware Native Species Commission and the Delaware Nature Society play an essential role in raising awareness and providing information on invasive plants to gardeners, landowners, and the general public. By understanding the potential harm of invasive species, individuals can make informed choices when selecting plants for their yards and contribute to the protection of Delaware's natural environments.

Ongoing Challenges and Efforts

Invasive plants in Delaware continue to pose challenges, with new species emerging and established ones adapting to the local environment. The work of organizations like the Delaware Invasive Species Council and the Delaware Native Species Commission is vital in monitoring, assessing, and managing these invasive species. Through research, policy development, and public education, Delaware aims to protect its native ecosystems and preserve the biodiversity of the state.

Invasive plant species in Delaware

Delaware has a number of invasive plant species, which are harmful to their non-native environments because they outcompete native plants and disrupt local ecosystems. Here is a list of some of the most common invasive plant species in Delaware:

Porcelain Berry (Ampelopsis glandulosa)

A perennial vine native to northern China and Japan. It grows quickly, smothering shrubs and trees by growing over them and blocking sunlight, eventually killing them. It is particularly prevalent in New Castle County.

Asiatic/Oriental Bittersweet (Celastrus orbiculatus)

A vine species similar to porcelain berry, native to eastern Asia. It grows up native plants and smothers them.

Japanese Honeysuckle (Lonicera japonica)

A vine species similar to porcelain berry and oriental bittersweet, native to Japan and eastern Asia. It grows up native plants and smothers them. Research has also shown that this plant often provides a habitat for ticks carrying Lyme disease bacteria.

Mile-a-Minute Weed (Persicaria perfoliata)

An annual plant that grows from seed every spring, slowly at first and then rapidly, overtaking small trees.

Callery or Bradford Pear (Pyrus calleryana)

A tree native to China and Vietnam, with white flowers. It is highly invasive and takes over fields.

Norway Maple (Acer platanoides)

A tree species that grows faster than native maples, creating dense shade that prevents other species from surviving. Its shallow root system also makes it difficult for native seedlings to thrive.

Burning Bush

A shrub native to central and northern China, Japan and Korea. It aggressively outcompetes native species and quickly reproduces from its fallen berries.

Japanese Barberry (Berberis thunbergii)

A shrub similar in appearance to the burning bush, native to Japan and eastern Asia. It has been found to often provide a habitat for ticks carrying Lyme disease bacteria.

Multiflora Rose (Rosa multiflora)

A species of rose native to eastern Asia, China, Japan and Korea, that has been causing problems since the 1980s. It grows and spreads quickly due to birds eating and dispersing its seeds. It creates dense thickets that exclude most native herbs and shrubs, and can be detrimental to the nesting of native birds.

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