invasive plants - university of tennessee

Chapter 25Invasive Plants

Learning Objectives1. Explain the historical and

political background on non-native, invasive plants

2. Identify the significant threats to native ecosystems of invasive plants

3. Explain the main principles of invasion

4. Explain economic and environmental impacts of invasive plants

5. Identify the main control guidelines for non-native, invasive plants

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Tennessee Master Gardener Handbook 688

Non-native, invasive plants are alien or exotic plants that pose major economic and environmental threats in each of

the United States. Non-native, invasive plants especially affect natural areas, greenways, streamside zones, forests and public rights-of-way. Managing these threats is expensive, but disregarding these threats allow the invasive plants and the problems they cause to become much worse. Other than in the agricultural sector, little has been done to curb this threat.

All non-native or exotic plants do not pose a threat. In fact, less then one percent of native plants become invasive. Presently, there are only 29 plant species listed by the Tennes-see Exotic Pest Plant Council posing severe threats and another 49 plant species posing significant threats to natural areas. Tables 1A and 1B list these plants. Eventually, state regu-lations will emerge in Tennessee to deal with these threats. Unfortunately, the only state regulation that currently exists is the agricul-tural noxious weed list. Some state agencies recently made it policy not to plant invasive

pest plants, but only a few are taking acting to eradicate or control existing invasions.

See Table 1A. Non-Native, Invasive Plants listed by the Tennessee Exotic Pest Plant Council as Posing Severe Threats, Rank 1, to Natural Areas and Table 1B. Non-native, Invasive Plants listed by the Tennessee Exotic Pest Plant Council as Posing Significant Threats-Rank 2- to Natural Areas.

It is difficult to predict which new non-na-tive plants will become invasive. This problem is compounded because the data about the impacts and management of existing non-native, invasive plants is only now being col-lected. Currently, a more systematic approach is needed to identify and predict non-native, invasive plants. Master Gardeners can partici-pate in this effort.

Costs of Non-native, Invasive PlantsIt is estimated that all invasive species, includ-ing bugs, plants and diseases for agriculture, forestry, environment, commerce, communities and households, cost the United States about $120 billion each year. These costs include lost crop production, power outages, loss of property value, increased operating costs, loss of game and loss of endangered species. Costs due to non-native plants alone may comprise roughly $35 billion each year. Residential, non-native, invasive plant control is estimated to cost $500 million each year and an esti-mated $1 billion each year is spent on invasive plant control on golf courses. It is estimated that 700,000 more hectares -1 hectare equals just over 2.4 acres- get invaded by non-native, invasive plants each year. Although precise costs and impacts have not been developed for Tennessee, it is likely that the numbers are growing.

The above being stated, specific costs for non-native, invasive plant removal can vary with the size of the plant and the size/severity of invasion. Costs can vary from a few cents per plant to hundreds of dollars for large trees. Also, additional costs are incurred if treat-ments need repeating or if sites need restoring to inhibit re-invasion. Some plants, such as

Invasive Plants

Federal Attempts to Control Invasive Plants

In 1999, Presidential Executive Order #13112 required federal agen-cies to take action against invasive plants, to organize the National Invasive Species Council and to develop a National Invasive Species Management Plan. In 2001, the Government Accounting Office Re-port GAO-01-724 cited that federal agencies were moving too slow in the fight against the growing threat of invasive species2. Nearly half of all Threatened and Endangered Species are in this condition, at least in part, because of non-native, invasive plants. The US For-est Service and National Park Service have identified invasive spe-cies as one of the top major threats to the sustainability of forests and wildlife habitat. The Animal and Plant Health Inspection Ser-vice (APHIS) has the main federal responsibility to enforce invasive plant laws1. The primary law is the Plant Protection Act that enables APHIS to stop or limit interstate movement of plants if deemed nec-essary to prevent introductions of plant pests or noxious weeds. As defined by public law, a noxious weed is defined as a plant or plant product that damages crops, livestock, poultry, irrigation, naviga-tion, natural resources of the United States, public health or other agricultural interests. Lack of funds has been seriously hindering progress to control invasions.


Table 1A. Non-Native, Invasive Plants listed by the Tennessee Exotic Pest Plant Council as Posing Severe Threats, Rank 1, to Natural Areas.

Scientific Name Common Name

Ailanthus altissima (Mill.) Swingle Tree of Heaven

Albizia julibrissin Durazz. Mimosa

Lonicera morrowii Gray Morrow’s Bush Honeysuckle

Alliaria petiolata (Bieb.) Cavara & Grande Garlic Mustard

Lonicera tatarica L. Tartarian Honeysuckle

Celastrus orbiculatus Thunb. Asian Bittersweet

Lonicera x bella Zabel Bell's Honeysuckle

Dioscorea oppositifolia L. Chinese Yam

Dioscorea bulbifera L. Air-potato

Lythrum salicaria L. Purple Loosestrife

Elaeagnus umbellata var. parviflora (Wall. ex Royle) C.K.Schneid. Autumn Olive

Elaeagnus pungens Thunb. Thorny Olive

Euonymus fortunei (Turcz.) Hand.-Mazz. Winter Creeper

Microstegium vimineum (Trin.) A. Camus Japanese Stiltgrass

Myriophyllum spicatum L. Eurasian Water-milfoil

Hedera helix L. English Ivy

Lespedeza cuneata (Dum.-Cours) G. Don Chinese Lespedeza

Paulownia tomentosa (Thunb.) Sieb. & Zucc. ex Steud. Princess Tree

Ligustrum sinense Lour. Chinese Privet

Ligustrum vulgare L. Common Privet

Lonicera fragrantissima Lindl. & Paxton January Jasmine

Phragmites australis (Cav.) Trin. ex Steud. Common Reed

Polygonum cuspidatum Seib. & Zucc. Japanese Knotweed

Nandina domestica Thunb. Sacred Bamboo

Pueraria montana var. lobata (Willd.) Maesen & S. Almeida Kudzu

Lonicera japonica Thunb. Japanese Honeysuckle

Rosa multiflora Thunb. ex Murr. Multiflora Rose

Lonicera maackii (Rupr.) Herder. Amur Bush Honeysuckle

Solanum viarum Dunal Tropical Soda Apple

Sorghum halepense (L.) Pers. Johnson Grass

Spiraea japonica L.f. Japanese Spiraea

The Cost of Treating Purple Loosestrife

One species, purple loosestrife, is es-timated to cost $45 million each year in control costs and wetland habitat loss. Furthermore, nearly 115,000 more hect-ares are invaded by purple loosestrife each year.


Table 1B. Non-native, Invasive Plants listed by the Tennessee Exotic Pest Plant Council as Posing Significant Threats-Rank 2- to Natural Areas.

Scientific Name Common Name

Alternanthera philoxeroides (Mart.) Griseb. Alligatorweed

Lysimachia nummularia L. Creeping Jenny

Melilotus alba Medikus White Sweet Clover

Arthraxon hispidus (Thunb.) Makino Hairy Jointgrass

Berberis thunbergii DC. Japanese Barberry

Miscanthus sinensis Anderss. Chinese Silver Grass

Melilotus officinalis (L.) Lam Yellow Sweet Clover

Murdannia keisak (Hassk.) Hand.-Maz. Asian spiderwort

Bromus japonicus Thunb. ex Murr. Japanese Bromegrass

Myriophyllum aquaticum (Vell.) Verdc. Parrot Feather

Bromus secalinus L. Rye Brome

Myriophyllum spicatum L. Eurasian Water-milfoil

Bromus tectorum L. Cheat Grass

Nandina domestica Thunb. Sacred Bamboo

Carduus nutans L. Nodding Thistle

Rorippa nasturtium-aquaticum (L.) Hayek Watercress

Mahonia bealei (Fortune) Carr. Leatherleaf Mahonia

Centaurea biebersteinii DC. Spotted Knapweed

Cirsium arvense (L.) Scop. Canada Thistle

Cirsium vulgare (Savi) Ten. Bull Thistle

Clematis terniflora DC. Sweet Autumn Clematis

Populus alba L. White Poplar

Conium maculatum L. Poison Hemlock

Potamogeton crispus L. Curly Pondweed

Coronilla varia L. Crown Vetch

Setaria faberi R.A.W. Herrm. Nodding Foxtail-grass

Daucus carota L. Queen Anne's Lace

Setaria italica (L.) P. Beauv. Foxtail-millet

Setaria pumila (Poir.) Roem. & Schult. Yellow Foxtail

Dipsacus fullonum L. Fuller's Teasel

Setaria viridis (L.) P. Beauv Green Foxtail

Euonymus alatus (Thunb.) Sieb. Burning Bush

Lolium arundinaceum (Schreb.) S.J. Darbyshire Tall Fescue

Hesperis matronalis L. Dame's Rocket

Tussilago farfara L. Coltsfoot

Verbascum thapsus L. Common Mullein

Hydrilla verticillata (L.f.) Royle Hydrilla

Vinca minor L. Common Periwinkle

Lespedeza bicolor Turcz. Bicolor Lespedeza

Wisteria sinensis (Sims) DC. Chinese Wisteria

Wisteria floribunda (Willd.) DC. Japanese Wisteria

Ligustrum japonicum Thunb. Japanese Privet


kudzu (Pueraria Montana) or Japanese hon-eysuckle (Lonicera japonica) are so invasive that they are treated as a block rather than as individual plants. In these cases, management is usually described in dollars/acre.

Planting Non-native, Invasive PlantsThe Tennessee Exotic Plant Pest Council (EPPC) lists some non-native, invasive plant species as illegal. These plants are under con-sideration for listing by the Tennessee Depart-ment of Agriculture, but Tennessee is reluc-tant to impose invasive plant restrictions on landowners. A few communities have volun-tarily developed lists of plants they no longer will consider for planting. However, very few communities have ordinances prohibiting the planting, propagation, selling and transporting of plants on the Tennessee EPPC list.

Outside these communities, the liabilities associated with planting non-native, invasive plants are ethical, ecological, economic and civil. Ethical liabilities refer to knowingly introducing a non-native, invasive plant when undesired consequences are known. Ecologi-cal liabilities refer to introducing a species that has, or could, significantly impact nearby natural areas and increase invasion pressures. Economic liabilities refer to the added mainte-nance cost to the management of natural areas and rights-of-way as well as the loss in habitat quality due to non-native, invasive plants. For example, it is estimated that land values have been lowered by as much as 20 percent, due to the invasions of kudzu and Chinese silvergrass. Finally, civil liabilities refer suing for damages if someone knowingly and intentionally plants invasive plants that can significantly affect someone else’s property.

Non-Native Plant Invasions in Native EcosystemsThere are several factors to consider when at-tempting understanding of the invasive plant problem. These factors include the principle of invasion, which help determine how to control the invasion; the cause of invasion; and the pathway of invasion, which can help deter-mine how to prevent more invasions. There are also economic and environmental impacts, both beneficial and detrimental, attributed to invasive plants. Because it is unlikely that all invasive plants can be controlled, yet the threat is large and the cost to control them is high,

Figure 1. Purple LoosestrifePhoto courtesy of UGA, bugwood.org

Figure 2. Tree of HeavenPhoto courtesy of UGA, bugwood.org

Figure 3. CogongrassPhoto courtesy of UGA, bugwood.org


it is important to make smart choices when choosing which species to control.

Principles, Causes and Vectors of InvasionThree phases can be identified for biological invasions: arrival, establishment and spread. Of all the exotic, alien, hybrid, non-native, non-indigenous, horticultural and genetically modified plant species brought into Tennes-see, approximately 10 percent or less are able to establish and sustain themselves as residents. Of this 10 percent, less than 1 percent will become aggressive enough to spread and pose a threat to native ecosystems.

Some traits can help predict which invasive plants will become established. These traits include fast growth, early maturity to flower-ing and seed production, high seed production, and high tolerance of varying site conditions. In today’s worldwide commerce and travel, in-vasive plants can spread at any distance in any direction. Thus, because of the increase in new plant arrivals, the chances of an undesirable plant species becoming established is raised.

The shift from establishment to spread is very hard to predict. It can be within a few years, as with Chinese silvergrass, or it can take many decades, as with Oriental bitter-sweet. The speed of the transition from arrival, to establishment, to spread, can be influenced by how much more of the same species arrives over a given time period. That is, repeated in-troductions raise the chances of establishment and spread.

The biology of the plant and the means of seed dispersal, including all sorts of propagule dispersal, affect the plant’s ability to spread. Plants can be dispersed by natural causes such as: wind, erosion, wildlife and natural forest disturbances. Plants can also be dispersed by human activities such as construction, com-merce, domesticated animals and interstate plant sales. Establishment is often influenced by the condition of the environment. Usually, but not always, some kind of forest disturbance leads to more aggressive plant invasions. Forest clearing, forest thinning, development, severe storms, flooding, drought, forest fire, over-browsing by deer, right-of-way construction and maintenance, and severe air pollution are examples of forest disturbance.

All this suggests that prevention, early detection and rapid response are vital to reduc-ing new invasive plant threats. Collectively, these have been the focus of national coopera-tive groups, several government agencies and environmental groups.

Human as Dispersing AgentsThe most common cause of non-native plant invasions is people. People transport new plants or seeds and people often cause the for-est disturbances that facilitate plant invasions. It has been the trend in Tennessee that plant invasions originate in urban areas and spread along highways, rivers and other kinds of rights-of-way. Invasions are further facilitated by increased development, shipping of nursery materials and landscaping.

Fortunately, there are several groups that are trying to stop the spread of non-native, invasive plants. These groups include right-of-way managers, nursery workers, seed and landscape industry workers, homeowners, communities, government agencies, developers and conservation volunteers-such as Master Gardeners. To successfully slow or halt the spread of non-native, invasive plants it is cru-cial that: pest plants are identified, enforceable limits are placed on their use, nursery workers and homeowners are educated on the threats they pose and on good non-invasive alterna-tives, a system of prevention is established, invasive plants are detected and controlled early, and communities are involved in taking actions to manage invasive plants.

Master Gardeners have the responsibil-ity to know which plants are invasive in their area. From this knowledge, it is important to help the public as well as the nursery and landscape industry understand the issues and possibly some good non-invasive alternatives. Voluntary Codes of Conduct are identified for the Gardening Public in the St. Louis Declara-tion, a workshop of the green industry to ad-dress invasive plants. Groups involved in this workshop at the Missouri Botanical Garden included the nursery industry, government, landscape architects, arboreta and botanical garden specialists, conservation organizations, university professors and garden club organi-zations. The eleven draft voluntary codes for the Gardening Public, as they appear in the St. Louis Declaration, are detailed in following Tip Box.


Voluntary Codes of Conduct for the Gardening Public1. Ask for only non-invasive species when acquiring plants. Only environmentally safe species should be planted in

your garden. Work towards and promote new landscape designs that are friendly to regional ecosystems.

2. Seek information on which species are invasive in your area. Sources could include botanical gardens, horticultur-ists, conservationists, and government agencies. Remove invasive species from your land and replace them with non-invasive species suited to your site and needs.

3. Do not trade plants with other gardeners if you know they are species with invasive characteristics.

4. Request that botanical gardens and nurseries promote, display and sell only non-invasive species.

5. Help educate your community and other gardeners in your area through personal contact, and in settings such as garden clubs and other civic groups.

6. Ask garden writers and other media to emphasize the problem of invasive species and provide information. Re-quest that garden writers promote only non-invasive species.

7. Invite speakers knowledgeable on the invasive species issue to speak to garden clubs, master gardeners, schools and other community groups.

8. Seek the best information on control of invasive plant species and organize neighborhood work groups to remove invasive plant species under the guidance of knowledgeable professionals.

9. Volunteer at botanical gardens and natural areas to assist ongoing efforts to diminish the threat of invasive plants.

10. Participate in early warning systems by reporting invasive species you observe in your area. Determine which group or agency should be responsible for reports emanating from your area. If no 800 number exists for such re-porting, request that one be established, citing the need for a clearinghouse with an 800 number and website links to information about invasive plant species.

11. Assist garden clubs to create policies regarding the use of invasive species in horticulture and in activities such as flower shows. Urge florists and others to eliminate the use of invasive plant material.


In response to this development, voluntary codes of conduct have been drafted for Exten-sion Agents, Master Gardeners and Specialists in Tennessee. The Voluntary Codes of Con-duct for Tennessee Extension Agents, Master Gardeners and Specialists is identified in the Tip Box below.

Management of Non-native, Invasive PlantsDifferent invasive plants pose different levels and different kinds of threats. Thus, to success-fully manage invasive plants, it is important to first determine which invasive plants need management. This can be a complex process. The list of invasive plants that pose severe or significant threats in Tennessee is neither complete, nor agreed upon by all segments of the public. However, factors that seem worthy of consideration for strategizing include:

▪ The ability to prevent, detect early or manage the invasion

▪ The extent and intensity of eco-logical damage to natural areas im-posed by the plant species as com-pared to other invasive plants

▪ The cost of thwarting or man-aging an invasion

▪ The economic importance of the species ▪ Whether suitable, non-invasive alter-

natives can be identified/developed

Unfortunately, information is incomplete in all of the above areas, making management decisions more difficult.

Determining the Economic Burden of Non-native, Invasive PlantsTo help determine if a non-native, invasive plant poses a large economic burden, some factors need to be considered. These factors include prevention capacity, early detection, rapid response, ecological and economic sever-ity, and priority rating. These terms and how they relate to non-native, invasive plants are described below.

Prevention capacity refers to the ability to stop new or additional introductions of a non-native, invasive plant species to a given area. If the species is already locally widely spread, preventive efforts could be futile and capac-ity would be rated low. However, if only a few

Voluntary Codes of Conduct for Tennessee Extension Agents, Master Gardeners and Specialists.

Mission: Assume the lead in your area for the promotion of non-invasive plants; awareness of non-native, invasive plants; and the shunning of the purchase or planting of non-native, invasive plants garden or landscape settings.

1. Learn to identify non-native, invasive plants in your area along with alternative control methods appropriate for different groups and conditions.

2. Develop a list of locally acceptable alternatives for non-native, invasive plants sold or sought in your area.

3. Educate gardeners, homeowners and the buying public about the threats from, identification of, control of and alternatives to non-native, invasive plants.

4. Seek to work with botanical gardens, arboreta and garden clubs on displays and projects that promote non-inva-sive plants and the management of non-native, invasive plants.

5. Establish working relationships with the Tennessee Nursery and Landscape Association, local nurseries, plant retailers, landscape architects and landscape maintenance workers to reduce or eliminate the sale and planting of non-native, invasive plants and seeds.

6. Collaborate with like-minded groups in the education and demonstration process utilizing shared materials, knowledge and resources.

7. Utilize plant sale events, other fund-raisers and Master Gardener events to educate the public about non-native, invasive plants and their alternatives.

8. Promote state and local policies and procedures that reduce or eliminate the commercial dispersal of non-native, invasive plants and their seeds in Tennessee.


plants are in the area, it may be effective to stop the distribution of those plants within the target area while eradicating known infesta-tions. In this case, prevention capacity would be rated high.

Inspections at commercial ports of en-try and setting up lines of defense, such as detection and control, along known fronts of

invasion can be important in prevention. In many cases, just informing key stakeholders of the threats and seeking voluntary regulation or codes of conduct can be helpful.

Early detection and rapid response are valu-able methods of controlling invasive species. These methods work best when areas are at least moderately free of the plant species of concern and when new invasions are occur-ring or are anticipated. This is true for whole regions or for smaller areas such as parks, gre-enways or wetland sites. Methods of available detection, whether they be by remote imagery, surveys or casual observations, are all appro-priate to consider.

Ecological severity refers to the impact a particular plant species has locally or in nearby regions. The impacts of non-native, invasive plants are only beginning to be documented. Most impacts are assumed based on indica-tors including: percent cover by the invasive plant, presence-absence across a range of sites, changes in various biodiversity indices, sus-pected changes in ecological functions such as nutrient cycling, changes in biomass composi-tion, and changes in habitat structure.

Economic severity refers to a combination of factors. These factors include impact to the nursery industry, costs associated with con-trolling infestations and costs associated with managing the damages they impose.

Priority rating is calculated by adding the ratings of prevention capacity, early detection and rapid response, ecological severity, and economic severity. Lower numbers indicate greater opportunities to control the species.

Compiling and evaluating prevention capacity, early detection and rapid response, ecological severity, economic severity, and pri-ority rating numbers is one method of deter-mining if a non-native invasive species poses an economic burden. See the Tip Box below for an example of how this evaluation method works.

Going through this type of evaluation process for a particular area helps reveal which non-native, invasive species to focus on in a particular area. Other important consider-ations are: ease of access, demonstration value and proximity to special areas. Getting started on the management of non-native, invasive plants is the hardest part, so it is best to start around areas or features that are of highest value to the community or to the individual.

Figure 4. Princess Tree or Royal Paulownia

Reproduction Rates of Various Non-native, Invasive Plants

A single princess tree (Paulownia to-mentosa) can produce an estimated 20,000,000 seeds a year and the light-weight seeds are easily dispersed by wind. Forests disturbed by fire and in-sect pests in the Great Smoky Mountains and Shenandoah National Parks have been heavily invaded by princess trees. Controlling the threat of this single spe-cies overtaking native vegetation has required substantial funds, labor, equip-ment and materials. Mimosa (Albizia julibrissin) and garlic-mustard plant (Al-liaria petiolata) have also posed a threat to ecosystems. Mimosa can produce 10,000 seeds per year with 90 percent of the seeds remaining viable for up to 5 years and a single inconspicuous garlic-mustard plant can produce thousands of seeds.


These areas might be trails, record-sized plants, areas where threatened or endangered species exist, special gardens and special cul-tural landscapes or views.

Table 2 is an example of how one might prioritize a list of 12 invasive plant species in the East Tennessee area. Priorities may change with geographic location and as better infor-

mation becomes available. The list of species is not meant to be inclusive nor does it include all of the severe non-native, invasive plants.

Control GuidelinesThere are socio-economic, ecological, physical, chemical and biological methods and strategies for controlling invasive plants. Usually a com-bination of methods is desirable, just as with integrated pest management (IPM). Several sources of information are available on control methods for various invasive plants. These include the Tennessee Exotic Plant Manage-ment Manual and the invasive plant fact sheets of the Plant Conservation Alliance.

Socio-economic controls refer to the buying and selling preferences of the nursery industry as well as the landscape and gardening public. Knowledge about the invasiveness of plants should help the nursery industry promote alternatives and provide guidance about what not to buy, plant or propagate among home-owners and gardeners.

Ecological controls are approaches resource managers, forest owners and other landowners can apply in the way they manage field edges, vegetation composition, forest disturbances and the density of vegetative cover. Generally, the idea is to crowd out invasive plant spe-cies by the use of a thick plant cover. Quickly planting disturbed areas with aggressive, non-

Evaluating the Economic Burdon of Purple Loosestrife

Purple loosestrife is ravaging wetlands throughout the Northeast. It is working its way south and poses a severe and expensive threat. Although the plant is generally not in Tennessee, it has been spot-ted in landscaping and has apparently been imported intentionally. According to Table 2, the prevention capacity is high (1) because there are few places where the plant occurs and it is possible to convince the nursery industry to ban importation, propagation, planting or transport of the species. Early detection and rapid re-sponse are also rated as high (1) because plants are usually located in highly visible locations and easily eradicated. Ecological severity is also rated as high (1) because of the huge damage imposed on wetlands in nearby regions. Economic severity is also rated as high (1) because of the many millions of dollars being expended in the Northeast to control the plant and the limited impact to the nursery trade of banning the plant. Purple loosestrife is worthy of high pri-ority while at its early stage of invasion where costs of prevention and early detection are relatively low.

Table 2. Example of a Method of Prioritizing Invasive Plant Species in Tennessee for Management.

SpeciesPotential

Prevention Capacity

Likely Effectiveness of Early Detection, Rapid Response

Anticipated Ecological

Severity

Expected Economic Severity

Priority Rating

Chinese silvergrass 2 1 1 2 high

Purple loosestrife 1 1 1 1 high

Cogongrass 1 1 1 1 high

Japanese knotweed 2 1 1 3 medium

Tree of heaven 3 3 1 1 medium

Japanese stiltgrass 3 2 2 1 medium

Oriental bittersweet 2 2 2 2 medium

Amur honeysuckle 4 4 1 2 low

Euro/Chinese privet 4 3 1 1 low

Kudzu 2 2 2 2 low

**This table is based upon opinion regarding number rankings and is provided for discussion purposes only. Numbers are based on some speculation along with experience and are only general estimates. Groupings such as high, medium, and low are more appropriate and relative only to the other species assessed in the Table.1=high, 2=moderate, 3=low, 4=noneThese numbers might change as more is learned about a species.


invasive plants is a big help. This is very im-portant in site restoration where sites become more open to sunlight because most invasive plants are not shade-tolerant. Also, if an area is to be disturbed, it is important to time this

disturbance when local invasive plant seeds are not being actively dispersed.

For more information on physical, chemical and biological controls of non-native, invasive species see the Tip Box below, Table 3, Chap-ter 19, Chapter 21 and Chapter 22.

SummaryNon-native, invasive plants should be a major concern to Master Gardeners. These plants can be devastating to natural areas and impose significant expenses. It is important to educate others about the threats of non-native, invasive plants, how they may be managed and how to avoid their being a problem. Following the suggested guidelines, it is important to take actions to reduce invasive plant threats in your community and with your neighbors. Alterna-tives to invasive plants need to be marketed. Those who plant, sell or propagate these pest plants should be encouraged to use alternative species. The top three things Master Garden-ers should teach the public about non-native, invasive plants are:

▪ Know which plants are prob-lems and how to identify them.

▪ Learn to manage these undesired plants and prevent their spread.

▪ Work together to find accept-able non-invasive alternatives.

Tips on Physical Control of Non-native Invasive Plants

Often it is important to time physical control efforts with specific seasons or conditions to be most effective. Exam-ples of this are pulling up plants when the soil is soft so the roots come up, clip-ping annual grasses before they go to seed and cutting plants during the early summer when root reserves are at their lowest.

The positive aspects of these approach-es are that no chemicals are involved, the response is immediately observable and non-target plants mixed in the invasive ones may be better protected. The nega-tive aspects are that it is generally only effective for small invasions; it can dis-turb the soil, making way for more plants to invade; it usually requires several years of follow-up treatment; and it requires much labor.

Table 3. Invasive Plant Controls Positive and Negative Attributes

Controls Positive Aspects Negative Aspects

Socio-economic Preventative; results may be wide-reaching; offers education to the gardening/landscaping public

Requires education of the nursery industry

Ecological Natural Time and labor intensive; requires educated decisions

Physical Effective for small areas; often natural

Labor and time intensive; soil disturbed allowing further invasion

Chemical Effective for large areas; less labor required; soil is undisturbed

May be wasteful, often unnatural; adds chemicals to environment; must follow specifications for usage

Biological Natural Must make sure only targeted species is affected


Terms To KnowAlien or exotic plantEconomic severityEcological controlsEcological severityInvasive plantSeed dispersalNative alternativesNon-native plantPest plantPrevention capacityPropagulePriority ratingSevere threatSignificant threatVector

Test Your Knowledge1. What are some ways non-native, invasive

plants may have entered Tennessee?

2. What is the best way to kill a woody, de-ciduous, non-native, invasive plant with foliar systemic herbicides, what time of year is generally best to apply the herbi-cide to the leaves?

3. What percentage of loss of land value can non-native plants cause?

4. What are the four liabilities associated with planting non-native, invasive plants?

5. Who has contributed to the problem with invasive plants?

ResourcesTennessee Exotic Plant Manual

tneppc.orgCenter for Invasive Species and Ecosystem

Healthbugwood.org

Alien Plant Working Group of the Plant Conservation Alliancenps.gov/plants/alien

National Invasive Species Council websiteinvasivespecies.gov

Southern Appalachian Man & Biosphere websitesamab.org/Focus/Invasive/about.html

USDA website on invasive speciesinvasive.org

invasive plants - university of tennessee

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