Don’t Buy Nonnative Invasive Plants — Even if You Can

• By Susan Martin
• /
• December 2018 - Vol.4 No.12
• /
• 2 Comments

People are becoming more aware of the broad repercussions of planting nonnative invasive plants. Some effects are scarily visual—twining vines of kudzu, English ivy (Hedera helix), and oriental bittersweet (Celastrus orbiculatus) transform highway borders of trees and shrubs into monstrous, green, shapeless hulks. Although less readily observable, the destruction of food-web interactions between insect specialists and native plants is an ominous transformation that poses long-term upheaval. Banning the sale of invasive plants, however, is not as straightforward as you might expect. This article will look at three aspects of dealing with nonnative invasive plants:

• Federal regulations
• Virginia state regulations
• How we can help as consumers

DEFINITION OF INVASIVE

Let’s first start with the definition of invasive plants according to the Virginia Department of Conservation and Recreation (DCR): Invasive plants are species intentionally or accidentally introduced by human activity into a region in which they did not evolve and cause harm to natural resources, economic activity or humans.

HOW NONNATIVE PLANTS ARE INTRODUCED

Nonnative plants and seeds are transported from one location to another through natural pathways, such as wind and currents, or through man-made pathways. The man-made introductions can be intentional or unintentional. The introduction of new-to-the-trade plants is one of the most lucrative areas of ornamental plant sales. According to an article by Virginia Cooperative Extension (VCE), data from six non-governmental agencies indicated that 34-83% of the total number of invasive taxa (species, varieties, or cultivars) in the U.S. had a horticultural origin. (In contrast to agriculture, horticulture does not include large scale crop production.)

FEDERAL GOVERNMENT OVERSIGHT

Many of us assume that once a plant is recognized as a nonnative invasive, its sale will be restricted by governmental oversight. However, progress is stymied by the conflicting interests of the stakeholders (environmental groups, academia, regulatory entities, and those in the ornamental horticulture industry, both sellers and consumers). Budgetary constraints at both federal and state levels also restrict the development of regulations and plans for enforcement.

“In this day and age of strapped budgets, the idea of passing simple legislation that says you can’t sell this plant and then trying to enforce it is going to be less productive than actually getting the industry on board and developing the mentality that plants they sell have to be safe,” says Doug Johnson, head of the California Invasive Plant Council.

There have been several major pieces of Federal regulation, plus an executive order by President Clinton, regarding “noxious weeds”:

• Federal Noxious Weed Act of 1974
• Amendment of the Act in 1990
• February 3, 1999, Executive Order 13112 (Clinton)
• Plant Protection Act of 2000

The term noxious weed, is defined in the federal Plant Protection Act ([2000] as “any plant or plant product that can directly or indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, poultry, or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment.”

The noxious weed laws have focused on problems related to agricultural crops, rather than on nonnative invasive plants encountered in natural or recreational areas or in home landscapes. In the U.S., noxious weeds are regulated by state or federal governments; invasive plants are identified on nonregulatory advisory lists.

STATE REGULATION

According to a 2013 paper published in Bioscience:

In the United States, only species listed on state or federal noxious weed lists are regulated. According to our analysis, these regulatory lists poorly represent invasive plants in unmanaged (i.e., nonagricultural) systems.

The study describes the role of nongovernmental state and regional invasive plant councils (IPCs) and exotic pest plant councils (EPPCs) that create and maintain nonregulatory lists of invasive species. In addition to IPCs, some state governments have created invasive species councils (ISCs), which maintain advisory roles for departments overseeing noxious weed lists. Unfortunately, the presence of invasive species on these lists generally carries no legal requirement for control or restriction of the plant’s entry to the state, and individuals may distribute and cultivate plants on these lists with impunity. The study compared noxious weed lists and invasive plant lists in each state. The authors found that, on average, there is little overlap between a state’s noxious weed list and its invasive plant list, meaning that invasive plants are not regulated if they are not also on the noxious weed list.

VIRGINIA STATE REGULATION

What progress have we made in Virginia? The Code of Virginia first addressed issues of noxious weeds, including control, transport and penalties, in 1970. The Virginia Noxious Weed Law was passed in 2003. As defined in the Code of Virginia:

“Noxious weed” means any living plant, or part thereof, declared by the Board through regulations under this chapter to be detrimental to crops, surface waters, including lakes, or other desirable plants, livestock, land, or other property, or to be injurious to public health, the environment, or the economy, except when in-state production of such living plant, or part thereof, is commercially viable or such living plant is commercially propagated in Virginia.”

Hedera helix ‘Thorndale’ Photo: Thayne Tuason, Wikimedia Commons

These last two exclusions mean that the sale of a plant cannot be prohibited if it is already being sold or propagated in the state.

In 2015, The Department of Agriculture and Consumer Services (VDACS) added several invasive species to be regulated under the Virginia Noxious Weeds Law. The regulation establishes two tiers of noxious weeds:

Tier 1: Any noxious weed that is not native to the Commonwealth that (i) has no known populations present in the Commonwealth or (ii) is not widely disseminated in the Commonwealth and for which successful eradication or suppression is likely.

Tier 1 includes: Salvinia molesta (Giant salvinia), Solanum viarum (Tropical soda apple) and Heracleum mantegazzianum (Giant hogweed).

Tier 2: Any noxious weed that (i) is not native to the Commonwealth, (ii) is not widely disseminated in the Commonwealth and (iii) for which successful suppression is feasible but eradication is unlikely.

Tier 2 includes: Imperata cylindrica (Cogon grass), Lythrum salicaria (Purple loosestrife, Ipomoea aquatic (Water spinach), Vitex rotundifolia, (Beach vitex), and Oplismenus hirtellus spp. undulatifolius (Wavyleaf basketgrass).

The new regulation also called for the creation of a Noxious Weeds Advisory Committee for the purpose of assisting VDACS in the evaluation and risk assessment of plants that may be declared noxious weeds in Virginia.

The Virginia Department of Conservation and Recreation’s Division of Natural Heritage currently identifies 90 invasive plant species (3 percent of the total Virginia flora) that threaten or potentially threaten natural areas, parks and other protected lands in Virginia. Virginia Invasive Plant Species List ranks the level of threat by nonnative species to forests and other natural communities, and to native species, as high, medium, low or early detection (to be watched). The list identifies three Virginia ecoregions: mountain, coastal, and piedmont. Although this list is a great resource for both homeowners and land managers, the DCR states:

The list is for educational purposes only and has no regulatory authority.

A subcategory of the Virginia Invasive Plant Species List includes the Virginia Invasive Plant Early Detection Species. These are species not yet widely established in Virginia but are known to be invasive in habitats similar to those found here.

THE THREAT FROM FUTURE INVASIVES

Despite the relatively low percentage of plants that ultimately become serious invaders, the large number of garden plants for sale makes the potential invasive nonnative plant list quite sizable. An inventory of North American seed and nursery catalogs (1988-1989) records almost 60,000 plant taxa sold. In 1996 the “tens rule” was proposed by Mark Williamson and Allistair Fitter (1996). This rule states that one in ten imported plant or animal species (brought into the country) appear in the wild (introduced, feral), and one in ten of those become an established self-sustaining population. One in ten of established plants become a pest (negative economic effect). Applying the tens rule to this 60,000 number and assuming half of these were nonnative to a particular area, approximately 3,000 plants would escape, 300 species would establish in the wild, and 30 would become pests. This might seem like a small number until we consider the serious impact of even one nonnative invasive species.

AN EXAMPLE: ENGLISH IVY

English ivy (Hedera helix) is present in twenty-eight states including Hawaii. It thrives in the southeast and in the mild climate of the Pacific Northwest. Native to Europe, western Asia, and North Africa, it was introduced to the U.S. by early European settlers.

Hedera helix, Charlottesville, VA Photo: Susan Martin

English Ivy prefers open forests but is adaptable to many habitats and moisture conditions. As a ground cover, this ivy chokes out other plants, creating an “ivy desert” where nothing else can grow. Vines climbing up tree trunks spread out and envelop branches and twigs, blocking sunlight from reaching the host tree’s foliage, thereby impeding photosynthesis. An infested tree will exhibit decline for several to many years before it dies. The added weight of vines makes trees susceptible to blowing over during storms.

English ivy has been in the Seattle area for only about 100 years. A survey conducted before conservation work started 15 years ago estimated that roughly 10 percent of the city’s 8,000 acres of public land were infested with invasive ivy. Between 2005 and 2011, the City of Seattle spent more than $8 million of public funds (plus $3 million from private sources) on the removal of English ivy in its parks through the Green Seattle Partnership effort to maintain healthy urban forests. Add 400,000 volunteer hours donated by Seattle residents during the same time period, and you get an idea of the cost of invasive English ivy in just one city. Despite public awareness and a sizeable commitment of assets to eradication of ivy, Seattle has not been able to pass legislation banning its sale.

A quarantine has been debated for Washington state, but it has been difficult to implement because there are over 300 cultivars of English ivy, and only some are invasive. According to Alison Halpern, executive secretary at the Washington State Noxious Weed Control Board, trying to control English ivy through regulation is a nightmare. For now, Halpern plans to work with nurseries to voluntarily halt sales of problematic varieties.

In 2010, Oregon banned the sale of English ivy.

In 2003, regulation was introduced into the Virginia Senate to recognize English ivy as a noxious weed and to prohibit its sale:

Noxious weeds. Declares English Ivy, and its hybrids and cultivars, a noxious weed and requires the Commissioner and the Board of Agriculture and Consumer Services to regulate the transport and sale of this weed under the Noxious Weed Law.

The proposed bill was withdrawn due to opposition and the unlikelihood of passing.

WHAT CAN WE DO?

Both Federal and Virginia state websites appeal to consumers to educate themselves about nonnative invasive plants and to learn about native plants that can be used as alternatives. Because it is very difficult to pass regulation, there is a strong effort to encourage producers and sellers in the horticultural trade to voluntarily restrict sales of nonnative invasive plants, and to provide information to consumers about native alternatives. Consumers are encouraged to help put pressure on the horticultural trade by being vocal about their preference for planting natives, and by showing this preference by not buying nonnative invasive plants. This effort is especially important because of restrictions in the Virginia code. Currently, if a plant is propagated in Virginia, or is already sold in the state through the horticultural trade, its sale cannot be prohibited. Many states, including Virginia, are organizing representatives from environmental groups, academia, regulatory entities, the ornamental horticulture industry, and consumers, to join forces in a united effort. Consumers can also make sure that nonnative invasives, such as English ivy, are not included in their home landscapes.

SOURCES

A special thank you to Ruth Douglas, Virginia Native Plant Society Invasive Plant Educator and participant in the Blue Ridge PRISM (Partnership for Regional Invasive Species Management)

“Federal Government’s Response for Invasive Species,” USDA, https://www.invasivespeciesinfo.gov/federal-governments-response-invasive-species

Noxious Weeds Program: Regulations, USDA, https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/sa_weeds/sa_noxious_weeds_program/ct_nwregs

U.S. Federal Noxious Weed List, Photos, https://www.inaturalist.org/guides/2459

Federal Noxious Weed Act of 1974, https://en.wikipedia.org/wiki/Federal_Noxious_Weed_Act_of_1974

Executive Order 13112 – Section 4. Duties of the Invasive Species Council, https://www.invasivespeciesinfo.gov/executive-order-13112-section-4-duties-invasive-species-council

“Virginia Invasive Plant Species List,” http://www.dcr.virginia.gov/natural-heritage/invsppdflist

“Virginia Invasive Plants Early Detection Species,” http://www.dcr.virginia.gov/natural-heritage/invsp-earlydetection

“Invasive Species, Laws and Regulations, U.S. Fish and Wildlife Service, https://www.fws.gov/invasives/laws.html

“Bad Seeds, Part 2 – Invasive plants in your local nursery,” https://www.scpr.org/news/2010/11/23/21166/bad-seeds-part-2-in

“Introduced, Invasive, and Noxious Plants,” https://plants.usda.gov/java/noxious?rptType=Federal

“Updates to State Regulations and Resources on Invasive Plants,” https://environment.arlingtonva.us/2015/04/updates-to-state-regulations-and-resources-on-invasive-plants/

2VAC5-317-20. Tier 1, Tier 2, and Tier 3 Noxious Weeds, https://law.lis.virginia.gov/admincode/title2/agency5/chapter317/section20/

“Invasive Plants — A Horticultural Perspective,” VCE, https://pubs.ext.vt.edu/426/426-080/426-080.html

“The Truth About English Ivy,”

greenseattle.org/wp-content/uploads/2015/12/English-Ivy-Brochure-Web-.pdf

“Oregon Bans Sale of English Ivy, Butterfly Bushes,” Oregon Business News, https://www.oregonlive.com/business/index.ssf/2010/02/oregon_bans_sale_of_english_iv.html

“Invasive Exotic Plants of the Southeast,” NC State, https://projects.ncsu.edu/goingnative/howto/mapping/invexse/englishi.html

“Rip the ivy out of your yard right now. Seriously,” https://kuow.org/stories/rip-ivy-out-your-yard-right-now-seriously/

California Invasive Plant Council, https://www.cal-ipc.org/

Invasive Plant Atlas of the U.S., https://www.invasiveplantatlas.org/subject.html?sub=3027

“Navigating the “Noxious” and “Invasive” Regulatory Landscape: Suggestions for Improved Regulation,” https://academic.oup.com/bioscience/article/63/2/124/533654

Regulations for the Enforcement of the Noxious Weeds Law, Virginia Register of Regulations, http://register.dls.virginia.gov/details.aspx?id=3649

Top Photo, Ivy in Wooded Glade, Acabashi, Wikimedia Commons, https://upload.wikimedia.org/wikipedia/commons/6/62/Wooded_glade_with_ivy.jpg