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Threats to Green Infrastructure and Invasive Species

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Overview

There are a number of invasive plants that currently threaten Bloomington to various degrees. Several of these are listed in Table 1 below. The following six invasive plant species represent the most significant threats to Bloomington and are discussed in more detail below: Brazilian elodea, sweet clover, tree-of-heaven, Japanese stilt grass, wintercreeper, and bush honeysuckle. For more information on these and other invasive plants, please visit the Indiana DNR's Invasive Species page.

Aquatic plants

Herbaceous plants

Trees

Grasses

Groundcover

Shrubs

Source: Indiana Department of Natural Resources 1.

Brazilian elodea (Egeria densa)

Sweet clover (Melilotus officinalis)

Tree-of-Heaven (Ailanthus altissima)

Japanese stilt grass (Microstegium vimineum)

Wintercreeper (Euonymos fortunei)

Bush honeysuckle (Lonicera spp.)

Eurasian watermilfoil (Myriophyllum spicatum)

Garlic mustard (Alliaria petiolata)

Norway maple (Acer platanoides)

Reed canary grass (Phalaris arundinacea)

Kudzu (Pueraria lobata)

Multiflora rose (Rosa multiflora)

Water hyacinth (Eichhornis crassipes)

Canada thistle (Cirsium arvense)

Autumn olive (Elaeagnus umbellata)

Quack grass (Elymus repens)

Japanese hops (Humulus japonicus)

Common privet (Ligustrum vulgare)

Yellow floating heart (Nymphoides peltata)

Purple loosestrife (Lythrum salicaria)

Siberian elm (Ulmus pumila)

Tall fescue (Festuca arundinacea)

Oriental bittersweet (Celastrus orbiculatus)

Japanese barberry (Berberis thunbergii)

Curly leaf pondweed (Potamogeton crispus)

Japanese Knotweed (Polygonum cuspidatum)

Black locust (Robinia psuedoacacia)

Maiden grass (Miscanthus sinensis)

English Ivy (Hedera helix)

European Highbush cranberry (Viburnum opulus v. opulus)



Buckthorn (Rhamnus cathartica)

Johnson grass (Sorghum halapense)

Crown vetch (Coronilla varia)

Burning bush (Euonymus alata)



White mulberry (Morus alba)

Reed grass (Phragmites australis)

Moneywort (Lysimachia nummularia)

Butterfly bush (Buddleia davidii)



Russian olive (Elaeagnus angustifolia)


Japanese honesuckle (Lonicera japonica)


Brazilian elodea (Egeria densa)

Dispersal

Brazilian elodea is native to regions of Brazil, Argentina, and Uruguay. As early as 1893, Brazilian elodea was collected in Long Island. By 1915, the plant was marketed to add oxygen to water. Today, the invasion of Brazilian elodea is most widespread along the East coast, though it is found across the US 2. In Indiana, the first invasion of a public body of water occurred in 2001 at Griffy Lake 3. This dense population is the northernmost known population of Brazilian elodea in the Midwest. The plant has been known to spread via the aquarium and water garden industry. Plants are often disposed of in natural waterways. It is still sold today under the name Anacharis. Brazilian elodea can reproduce from plant fragments, so boating and recreation can contribute to the spread of the species.

Brazilian Elodea Brazilian elodea. Washington State Department of Ecology

Impacts

Brazilian elodea is currently considered the top invasive threat to Bloomington 4. The species can rapidly grow and reproduce, quickly creating dense mats. These mats can crowd or shade out native aquatic plant species. Recreation, such as boating or swimming, can be inhibited by the mats. The mats can become so dense that water movement is limited and fish populations can suffer due to poor habitat quality. Water intake pipes are often clogged by Brazilian elodea fragments. The mats are not aesthetically pleasing and may cause problems with water quality by trapping sediment and other pollutants.

Management

Brazilian elodea is difficult and expensive to control. Chemical control is available for quick and complete elimination. However, there are not any selective herbicides for Brazilian elodea, so some native plants would be lost using this control method. Despite concerns raised by Bloomington officials surrounding the use of chemical herbicides in Griffy Lake, the Department of Natural Resources decided to use an herbicide named 'Sonar' in an attempt to eradicate Brazilian elodea. An additional herbicide, 'Reward', will be used for spot treatments when needed. These chemicals are approved by the EPA for aquatic invasive species removal and are not believed to harm fish or other aquatic wildlife. Additionally, to prevent further spread, the only watercrafts permitted on Griffy Lake are on-site rental boats, which do not have motors 5.

What You Can Do

Bush honeysuckle (Lonicera maackii, L. tatarica, L. morrowii, L. X bella)

Dispersal

Bush honeysuckle is a common name for a group of honeysuckles originating in Eurasia. In the US, bush honeysuckle was introduced for ornamental purposes, wildlife habitat, and erosion control. Bush honeysuckle has invaded the Great Plains and southern New England, and it has spread south to Tennessee and North Carolina. Indiana invasions are particularly severe in the northern and central portions of the state. The shrub is relatively shade-intolerant, but can move in and dominate a forested area after a disturbance 6. Bush honeysuckle is the greatest terrestrial invasive plant threat to Bloomington. The shrub has taken over large portions of Lower Cascades Park and is moving into the Griffy Nature Preserve 7.

Bush Honeysuckle Bush honeysuckle. © Kenneth R. Robertson, Illinois Natural History Survey.

Bush honeysuckle grows so dense that the understory is completely shaded out. Thus, soil is left bare and is particularly vulnerable to erosion. Tree regeneration is impeded and succession is limited. Available wildlife food and cover is reduced. Bird nests often experience more predation because nests in honeysuckle are more visible than nests in native shrubs. Some species of bush honeysuckle are allelopathic, which means they release chemicals into the soil that are toxic to other plants.

Management

Bush honeysuckle is particularly difficult to control. For small invasions, hand removal may be effective. Dense invasions often require chemical control. Foliar applications of systemic herbicides can be applied in the fall after native species are dormant. For well-established populations, cutting the shrubs to ground level and applying herbicide to the stumps may be the best control option.

What You Can Do

White and Yellow Sweet clover (Melilotus alba, M. officinalis)

Dispersal

Sweet clover is native to the Mediterranean, central Europe, and many parts of Asia. In the 1600s, sweet clover was brought into the US for livestock grazing and honey production. Sweet clover can now be found inhabiting all 50 states, but it is particularly dominant in the upper Midwest and Great Plains region. Sweet clovers fix nitrogen in the soil, and thus are often purposely planted for soil enhancement. Also, sweet clover is promoted as a good cover for wildlife. Sweet clovers are biennials and set seed and die in the second year of growth. Seeds can last up to 30 years. Disturbance, especially by fire, promotes sweet clover germination and growth 8.
Sweet Clover White Sweet Clover. © John M. Randall/The Nature Conservancy.

Impacts

In Bloomington, the Parks and Recreation Department spends a lot of time and effort to remove sweet clover from Bryan Park and Miller-Showers Park 9. Sweet clover is an aggressive, weedy plant that can take over landscapes. Native prairies and savannas are degraded by large populations of sweet clover. The plant overtops and shades out native plant species. Sweet clover also tends to limit available nutrients and moisture necessary for native plants.

Management

In small areas, hand pulling first year growth of sweet clover is an effective means of control. Second year plants can also be pulled before flowers develop, but this is more difficult because of the depth of the tap root. Cutting at ground level with brush loppers or a power brush-cutter can also work. If prescribed burning is an option in the invaded area, burns two years in a row have shown success at removing sweet clover stands. Systemic herbicides are another option, but care must be taken to avoid non-target plants.

What You Can Do

Tree-of-Heaven (Ailanthus altissima)

Dispersal

Tree-of-Heaven is a native tree of China. In 1784, the tree was introduced in Pennsylvania by an American gardener. By 1840, Tree-of-Heaven was available from many nurseries. In the mid-1800s, Chinese who entered California as part of the Gold Rush brought the tree with them, and it is frequently found at abandoned mine sites today. Tree-of-Heaven can now be found across the US in 42 states. Tree-of-Heaven rapidly spreads due to its prolific seed producing capabilities. One report suggests that a single tree can produce 325,000 seeds annually. Additionally, Tree-of-Heaven can re-sprout vegetatively from roots, fragments, or cut stumps. The tree can sprout nearly anywhere, whether the location is urban or rural 10.

Tree of Heaven Tree-of-Heaven. © Jackie Miles and Max Campbell.

Impacts

The rapid growth and dense stands of Tree-of-Heaven can overrun native species. Tree-of-Heaven can quickly dominate a landscape and produce impenetrable thickets. The tree is also allelopathic, which means the roots produce toxins that inhibit the growth of other species. Root systems of Tree-of-Heaven are also problematic and can damage foundations and sewers.

Management

Young seedlings may be pulled by hand or dug up, but care must be taken to remove all tree parts to avoid re-sprouting. Cutting alone will lead to re-sprouts, but if cutting is done year after year during early summer, the tree may eventually succumb to exhaustion of resources. Because of the potential for severe allergic to Tree of Heaven, anyone seeking to eradicate it by hand should take precautions such as using gloves, wearing long pants, etc. Herbicides may be the most effect control method. Foliar application on green leaves can be particularly effective, but overspray and non-target species should be avoided.

What You Can Do

Japanese Stilt Grass (Microstegium vimineum)

Dispersal

Japanese stilt grass originates from Asian countries, such as from Japan, Korea, China, Malaysia and India. In the United States, the grass was first introduced in Tennessee sometime around 1919. The initial introduction was likely due to the use of Japanese stilt grass for packaging material. Japanese stilt grass is now found in 16 states in the eastern US, including Indiana. The spread of stilt grass is facilitated through seed dispersal and vegetative means. A single plant can produce 100 to 1000 seeds that can remain viable for five or more years 11. Seeds are transported by water, wildlife, and humans (by footwear and cars). The Indiana Chapter of the Nature Conservancy has found that Japanese stilt grass is currently approaching the Bloomington area. Within a few years, stilt grass could completely cover local forest floors. In fact, a nearby infestation has recently been found in Beanblossom Bottoms in northwest Monroe County 12.

Japanese Stilt Grass Japanese Stilt Grass leaves. © John M. Randall/The Nature Conservancy.

Impacts

Japanese stilt grass is a generalist species, meaning the plant can tolerate and succeed in a variety of conditions. Stilt grass can invade wetlands, woodlands, stream banks, fields, ditches, lawns, and gardens. The grass can inhabit low-light or recently disturbed areas as well. Stilt grass threatens native species by limiting available sunlight and nutrients. Deer do not browse stilt grass, thereby putting additional stress on the native species that remain #13. Patches can spread quickly and eventually dominate the landscape.

Management

Prevention of an invasion is the best control option for Japanese stilt grass. Early management of new invasions can prevent establishment. Stilt grass is an annual grass with shallow roots and can be effectively managed by hand pulling prior to fruiting. Mid- to late-summer is the easiest time to hand-pull, especially if the soil is moist. If the plants have not gone to seed, the grass can be piled to dehydrate. If they are pulled with seed, the plants should be bagged and disposed of. This process should be continued each year until the seed bank has been depleted. Stilt grass can also be mechanically cut down in late summer during flowering, but before seeds are present. Chemically, excessive invasions can be controlled with glyphosate. Care must be taken during application, because glyphosate kills native species as well.

Japanese Stilt Grass Invasion Japanese Stilt Grass infestation. © John M. Randall/The Nature Conservancy.

What You Can Do

Wintercreeper (Euonymus fortunei)

Dispersal

Wintercreeper is native to China, but was introduced in the US in 1907 as an ornamental groundcover 14. This invasive species is currently found throughout the eastern US. In Bloomington, wintercreeper has extensively invaded Latimer Woods, 15 as well as Dunn's Woods on the IU campus 16. Wintercreeper can spread vegetatively from shoots produced along branches or from rootlets spread along the plant's stem. Wintercreeper produces fleshy fruits, which are eaten by wildlife, thus facilitating seed dispersal. This ornamental is known to escape gardens and invade forests and riparian areas. Water is another means of dispersal.

Winter Creeper Wintercreeper. © Will Cook.

Impacts

Wintercreeper can tolerate harsh growing conditions and grows quickly, depriving native species of space and sunlight. Wintercreeper can further hinder natives by depleting soil nutrients and moisture. Additionally, wintercreeper can form a dense mat, which blocks sunlight and prevents growth or regeneration of native species. Wintercreeper can eventually overtop trees and impede photosynthesis.

Management

Bloomington Parks and Recreation spent $6,500 in spring 2006 to control wintercreeper in Latimer Woods 17. Mechanically, wintercreeper can be removed by grubbing, which involves removing the entire plant and roots. This method is labor intensive but effective for small invasions. Any root, stem, or fruits could lead to resprouting, so these parts should be bagged and disposed of. Juvenile plants can be hand pulled. Both cut stem and foliar chemical applications are effective. Cut stem treatments involve cutting the plant as close to the ground as possible and applying an herbicide (such as Roundup or Garlon) to the stem. This method is preferable where wintercreeper has grown into canopies or is surrounded by non-target species. Foliar applications can control large invasions. This treatment involves spraying all of the foliage with herbicide. With this method there is more risk to non-native species.

What You Can Do


A Note on Herbicides:

Though herbicides may be the only option in extreme invasions by exotic species, it must be noted that there are many reasons not to use herbicides. Herbicides are often toxic chemicals that are hazardous to human health. Adverse health effects can include damage to the nervous system, lungs, reproductive organs, immune system, and hormone balance. Also, herbicides can cause birth defects and cancer 18. Chronic, repeated exposure can cause neurological damage, such as fatigue, depression, and tremors 19. Children are particularly vulnerable both because of their developmental stage and likelihood to contact herbicides when playing outside. Chemicals used for lawncare have even been linked to higher risks for cancer in pets 20. Herbicide applications do not remain on target species indefinitely, but instead are known to contaminate water and air. For example, over 60 percent of air sampled by the US Geological Survey contained the common herbicide 2, 4-D 21. Once the chemicals have entered the atmosphere or water, fish or birds can be negatively impacted. The EPA found that minute concentrations of common herbicides are linked to genetic damage in fish 22. Despite the risks, enormous quantities of these chemicals are used each year because of the quick and easy solution they provide.

References

1. Indiana Department of Natural Resources. Invasive Species.

2. Indiana Department of Natural Resources. March 2005. Aquatic Invasive Species: Brazilian elodea (pdf).

3. Aquatic Control, Inc. 2007. Griffy Lake Aquatic Vegetation Management Plan 2007 Update-Draft (pdf).

4. Steve Cotter, City of Bloomington Parks and Recreation. Personal Communication. September 27, 2006.

5. Journal and Courier Online. March 26, 2006. DNR to eradicate weed from Bloomington Lake.

6. Invasive Plant Species Assessment Working Group. December 2004. Invasive Plant Species Fact Sheet: Asian Bush Honeysuckle (pdf).

7. Steve Cotter, City of Bloomington Parks and Recreation. Personal Communication. September 27, 2006.

8. Wisconsin Department of Natural Resources. September 2004. Fact Sheet: White Sweet Clover.

9. Steve Cotter, City of Bloomington Parks and Recreation. Personal Communication. September 27, 2006.

10. Plant Conservation Alliance's Alien Plant Working Group: Least Wanted. Tree-of-Heaven.

11. Plant Conservation Alliance's Alien Plant Working Group. May 20, 2005. Fact Sheet: Japanese Stilt Grass.

12. Ellen Jacquart, Indiana Chapter of the Nature Conservancy. Personal Communication. October 6, 2006.

13. Plant Conservation Alliance's Alien Plant Working Group. May 20, 2005. Fact Sheet: Japanese Stilt Grass.

14. Plant Conservation Alliance's Alien Plant Working Group. May 20, 2005. Fact Sheet: Climbing Euonymus (pdf).

15. Steve Cotter, City of Bloomington Parks and Recreation. Personal Communication. September 27, 2006.

16. Heather Reynolds, Indiana University. Personal Communication. September 16, 2006.

17. Steve Cotter, City of Bloomington Parks and Recreation. Personal Communication. September 27, 2006.

18. P.J. Landrigan et al. 1999. Pesticides and innercity children: Exposures, risks, and prevention. Environmental Health Perspectives. 107: 431-437.

19. F. Kamel et al. 2005. Neurologic symptoms in licensed private pesticide applicators in the Agricultural Health Study. Environmental Health Perspectives 113:877-882. .

20. L.T. Glickman et al. 2004. Herbicide exposure and the risk of transitional cell carcinoma of the urinary bladder in Scottish Terriers. Journal of American Veterinary Medical Association. 24: 1290-1297.

21. C. Cox. 2006. Ten reasons not to use pesticides. Journal of Pesticide Reduction. 26: 10-12.

22. C. Cox. 2006. Ten reasons not to use pesticides. Journal of Pesticide Reduction. 26: 10-12.