Invasives

An invasive plant is not native to our region and has negative effects on our economy, environment, or human health.

Invasive plants spread aggressively and cause major environmental changes such as the elimination of native plant populations, which is detrimental for insects and pollinators that depend upon these native plants.

Exotic species are those that do not naturally occur in our region, but have been introduced by humans, either intentionally or accidentally, allowing the species to cross a natural barrier to dispersal.

It is true that the native range of plants can naturally expand in response to climate change and other factors over long periods of time. However, the introduction of exotic plants by humans allows the species to cross some barrier to dispersal, such as an ocean, vast desert, or mountain range, which prohibits natural range expansion.

While the introduction of exotic species such as insects or fungal pathogens is typically accidental, the vast majority of exotic plant species are introduced intentionally for purposes such as ornamental landscaping, livestock forage, and agriculture.

No, only a small portion of exotic plants ever escape cultivation, and only a small portion of those that escape ever become truly invasive. Many exotic plants, including virtually all major agricultural crops, are important for our economy, culture, and nutrition. However, the small percentage of exotic plants that do become invasive can have devastating consequences for the environment.

Even though most non-native plants used for landscaping are not invasive, exotic plants provide far fewer resources for native wildlife such as butterflies and pollinators compared to native plants.

You may have the impression that the fruits of exotic landscaping shrubs are good for birds and other wildlife. However, many of the worst invasive shrubs in the United States, such as bush honeysuckle, produce fruits with poor nutritional value compared to the native shrubs that are displaced by their invasion. When birds eat these fruits they disperse them widely, promoting invasion with negative consequences for our natural areas and the wildlife that depend upon native plants.

Invasive species are estimated to costs the US economy $120 billion per year, with invasive plants alone estimated to costs $27 billion per year. As a local example, approximately one-third of Missouri is covered by forested land, and the timber industry creates thousands of jobs and contributes about $3 billion each year to Missouri’s economy. The dense shading caused by bush honeysuckle and other invasive shrubs inhibits oak regeneration. If the invasion continues unabated, Missouri’s oak forest could decline as mature trees die without replacement.

In the Saint Louis region, a recent study from researchers at Washington University found that areas infested with bush honeysuckle have an increased abundance of the tick species that spread Lyme disease and Ehrlichiosis (a serious tickborne bacterial infection). Another recent study from the University of Illinois found that the displacement of native shrubs by invasive bush honeysuckle and autumn olive led to increased survival and abundance of the common house mosquito, the vector for West Nile Virus.

Invasives plants can prevent the enjoyment of our woodlands and stream banks for hiking, cycling, horseback riding, birding, hunting and other outdoor recreation. Thorny multiflora rose, dense stands of honeysuckle, Bradford pear, burning bush and other invaders can form impenetrable thickets in the understory of once open native forests and grasslands. For anglers and boaters, dense mats of aquatic invasives like Eurasian water milfoil can snag fishing lines and clog boat motors.

Invasive plants pose a major threat to biodiversity. It is estimated that 40% of species listed as endangered or threated in the United States have become imperiled due to invasive species alone or their combined impact with other destructive forces.

Invasive plants spread aggressively and cause major environmental changes such as the decline or complete elimination of native plant populations, which in turn impacts the insects and pollinators that depend upon native plants.

Some invasive plants can completely change the natural habitat they invade, such as the conversion of native grasslands or woodlands into dense shrub thickets.

Other invasive plants cause damage in more subtle ways. They alter the composition of the soil or change water chemistry in our streams, making it difficult for other plants, insects, and microbes to live there. They can also change the natural fire cycle of native ecosystems or increase soil erosion.

Even more subtly, some invasive plants can hybridize with native plants. Over time, this can completely wipe out the native plant. For instance, in the Saint Louis region, invasive oriental bittersweet can hybridize with the native American bittersweet.

Even the most severe invasions can begin with only a few escaping plants, which initially spread with little attention. Public awareness generally occurs only once an invasive species becomes so widespread that it is impossible to overlook. Unfortunately, at this later stage in the invasion process, control requires intense effort and widespread eradication is unlikely. However, if invasive species are detected early, then eradication is feasible with modest effort.

A proactive response requires early detection. The Early Detection and Distribution Mapping System (EDDMapS) is a web-based mapping system for documenting invasive species distributions. The Invasive Plant Atlas of the United States displays distributions maps from the EDDMapS, providing a valuable resource for conservation agencies and land managers. As a useful resource for the gardening public, the Garden’s Plant Finder includes links to these maps for species known to be invasive in the United States.

The gardening public might note that a distribution map does show that an invasive plant occurs in their county, or even their state, and conclude that it is not a concern where they live. However, this is not necessarily the case. Although many invasive species can tolerate a wide range of climates, it is unlikely that a species only known to be invasive in Southern Florida poses a threat in Saint Louis. However, species that are invasive in climatically similar regions such as parts of the Midwest, Mid-South, and Mid-Atlantic are also capable of invading our region.

Invasive species distribution maps underestimate the true distribution of species, since each county record must be formally documented and confirmed by an expert. An invasive species may actually be common in a particular county, but the distribution will only show a record for that county if this data has been properly reported. For instance, the distribution map for Japanese Wineberry (Rubus phoenicolasius) would suggest that it does not occur in Missouri, but it has actually been collected in the past two decades from seven Missouri counties, with vouchers in the Garden herbarium that have not yet been incorporated into the distribution map below (EDDMapS). Despite the shortcomings of this distribution map, the invasion of Japanese wineberry to the east of Saint Louis indicates that this species is capable of invading our region. The distribution map for wintercreeper (Euonymus fortunei) includes every single county in Indiana, but only several scattered counties in Missouri and Illinois. In reality, wintercreeper is one of the worst invasive plants in much of Illinois and Missouri; the distribution has simply been documented more comprehensively in Indiana. 

The science of invasion biology and the history of past invasions demonstrate that invasive species in climatically similar regions that do not yet occur in the St. Louis area are capable of invading our region, should not be planted in gardens, and should be eradicated upon detection. For instance, bush honeysuckle (Lonicera maackii) was first documented to escape cultivation in the 1920s near the Morton Arboretum in Chicago. By the 1950s its invasion was widespread to the east of Saint Louis, but bush honeysuckle was not documented outside of cultivation in Missouri until 1983. Although this invasion occurred later here, bush honeysuckle is arguably the worst invasive species in St. Louis. It is important that we learn from the past and take proactive measures against other invasive species spreading into our region. If we wait to take action until these emerging invasives are widespread, their control will be far most costly and less effective.

Bush Honeysuckle (Lonicera maackii, Lonicera x bella)

Autumn olive (Elaeagnus umbellata)

Amur corktree (Phellodendron amurense)

Burning bush (Euonymus alatus)

Callery Pear (Pyrus calleryana) cultivars (Bradford Pear, Chanticleer, Aristocrat, and others)

Chinese silvergrass (Miscanthus sinensis)

Chinese wisteria (Wisteria sinensis)

Common buckthorn (Rhamnus cathartica)

Common reed (Phragmites australis var. australis)

Crown vetch (Securigera varia)

Garlic mustard (Alliaria petiolata)

Golden rain tree (Koelreuteria paniculata)

Hardy pampas grass, plume grass, ravenna grass (Saccharum ravennae)

Japanese barberry (Berberis thunbergii)

Japanese honeysuckle (Lonicera japonica)

Japanese hop (Humulus japonicus)

Japanese knotweed (Fallopia japonica)

Japanese stiltgrass (Microstegium vimineum)

Japanese wisteria (Wisteria floribunda)

Hydrilla (Hydrilla verticillata)

Kudzu (Pueraria montana)

Multiflora rose (Rosa multiflora)

Oriental bittersweet (Celastrus orbiculatus)

Princess tree (Paulownia tomentosa)

Privet (Ligustrum spp.)

Purple loosestrife (Lythrum salicaria)

Sericea lespedeza (Lespedeza cuneata)

Spotted knapweed (Centaurea stoebe)

Tree-of-heaven (Ailanthus altissima)

Wintercreeper (Euonymus fortunei)

BiodiverseCity St. Louis is a growing network of organizations and individuals throughout the greater St. Louis region who share a stake in improving quality of life through actions that welcome nature into our urban, suburban and rural communities. The BiodiversCity website contains frequently updated information on current events and volunteer opportunities, many of which are related to invasive species control.

Operation Wild Lands (OWLS) is a community-based partnership coordinated by the Open Space Council that prepares citizen volunteers of all ages to restore and maintain public lands throughout the St. Louis region.  The Open Space Council coordinates many volunteer opportunities related to invasive species control.

Bring Conservation Home is a program of the St. Louis Audubon Society that provides advice for landscaping with native plant species, the removal of invasive plant species, water conservation on the urban landscape, and other stewardship practices that promote healthy habitat for birds, native wildlife and people.

Look for classes and workshops for working with native plants as an alternative to invasives:

• Missouri Botanical Garden gardening and landscaping classes
• St. Louis Community College gardening and horticulture classes
• Operation Brightside events

• The Garden has released a brochure about bush honeysuckle for the gardening public.
   
• BiodiverseCity STL: Honeysuckle Sweep Week
   
• Quartz Magazine (Feb. 6, 2016): The race to outsmart invasive plants before they get the best of us
   
• Conservation Magazine (July 14, 2015): To stop West Nile, go native
   
• The Atlantic (Oct. 4, 2015): How eBay could be messing up the world’s ecosystems
   
• Science Magazine (Jan. 30, 2015): Invasive plants taking over the US
   
• TechLine Invasive Plant News (regularly updated): Research and tips for invasive species management

• The Shaw Nature Reserve’s manual to the control and identification of invasive species provides detailed instructions for control and suggestions for native alternatives for many of the worst invasive species in the Saint Louis region.
   
• The Missouri Department of Conservation (MDC) invasive plants page contains useful resources for the identification and control of more than 25 of the most common invasive plants in Missouri.
   
• GrowNative! helps protect and restore biodiversity by increasing conservation awareness of native plants and their effective use in urban, suburban, and rural developed landscapes.
   
• The Missouri Invasive Plant Species Task Force (MoIP) is a multi-agency, multi-industry networking and advocacy group to bolster statewide efforts to identify and control the invasive plant species that severely impact native biodiversity.
   
• The Midwest Invasive Plant Network (MIPN) is diverse group of participants and partners with the mission of reducing the impact of invasive plant species throughout the Midwest. Their website includes many useful resources for invasive species identification, control, and education, and research, such as this informative brochure on emerging invasive species to watch out for in the Midwest.
   
• The Invasive.org website contains numerous resources for invasive species of the United States, including a vast library of invasive species images, and useful advice for invasive species control.
   
• In December 2001, experts from across the globe met in St. Louis, Missouri to explore and develop workable voluntary approaches for reducing the introduction and spread of non-native invasive plants, which are serious threats to protecting biodiversity and ecosystems in the United States and other countries. The Workshop on Linking Ecology and Horticulture to Prevent Plant Invasions was convened by the Missouri Botanical Garden and the Royal Botanic Gardens, Kew; and produced these Voluntary Codes of Conduct for botanical institutions.

Herbicides and Invasive Species: The decision whether or not to use herbicides should be based on the scale and context of an infestation and the feasibility of alternative control methods. The judicious use of herbicides is often the most effective means of controlling invasive species, but careless or uneducated herbicide use can result in collateral damage to non-target vegetation and other ecological harm. Although the Missouri Botanical Garden does not explicitly endorse the use of any herbicide product, it is important that homeowners who chose to use herbicides understand correct application practices. It is important to understand the appropriate herbicide type, concentration, and application method for the control of each individual invasive species. Always follow label instruction and use personal protective equipment.

Herbicide advice for homeowners is a brochure created by the Florida Exotic Pest Plant Council with useful information about some of the most common herbicides used for invasive species control. The Clifftop Alliance in Illinois has also compiled some useful information on the use of herbicides for invasive plant control.