• Topics: School of Forest Resources and Conservation  |  Natural Area Weeds  |  Invasive Weeds  |  Demers, Chris  | Long, Alan J 

Controlling Invasive Exotic Plants in North Florida Forests¹

Of the more than 4,000 known plant species growing in Florida, approximately 30% are not native to Florida or the Southeast. Organisms are considered non-native when they occur artificially in locations beyond their known historical native ranges. The term non-native can refer to species brought in from other continents, regions, ecosystems and even other habitats. The most important aspect of a non-native (exotic) plant is how it responds to a new environment. An invasive species is one that displays rapid growth and spread, allowing it to establish over large areas. Invasive species are free from the complex array of natural controls, including herbivores, parasites, and diseases, that are present on their native lands. The term noxious is a legal designation used specifically for plant species that have been determined to be major pests of agricultural ecosystems and are subject, by law, to certain restrictions.

Invasive non-native organisms are one of the greatest threats to the natural ecosystems of the United States. According to the U.S. Fish & Wildlife Service, an estimated 42% of the nation's endangered species have declined as a result of encroaching invasive species. Invasive species cause billions of dollars in economic losses and expenditures each year for agriculture, forestry, range lands and roadways management (Westbrooks 1998). Known ecological impacts of invasive plants include: reduction of biodiversity, loss of and encroachment upon endangered and threatened species, loss of habitat for native insects, birds and other wildlife, alterations to the frequency and intensity of fires and disruption of native plant-animal associations such as pollination, seed dispersal and host-plant relationships. In addition, invasive plants can hybridize with native plants and alter their genetics; they grow rapidly, sometimes girdling native shrubs and trees; they increase the incidence of plant disease and stress in forested areas; and they reduce the amount of space, water, sunlight and nutrients that would otherwise be available for native species.

This publication describes many of the current methods being used to manage some of the more common and troublesome invasive exotic plants in north Florida forests. Consult the sources referenced at the end of the paper for additional details about these and several other methods. This publication is intended to assist private forest landowners in managing their existing forests or establishing new plantations. All of the control methods involve some combination of mechanical and chemical treatments. Biological control agents for some of these plants are currently under investigation. Pictures of each species can be found at the following Web sites: http://plants.ifas.ufl.edu/ie6/index.html or in Langeland and Burks' book, "Identification and Biology of Non-Native Plants in Florida's Natural Areas."

Disclaimer

The use of trade names in this publication is solely for the purpose of providing information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other suitable products.

Treatment recommendations involve general herbicide prescriptions that have yielded acceptable levels of control in experimental trials. However, these recommendations are not guaranteed to work on every site. Most herbicides are applied in some combination with water and a surfactant (wetting agent). Always follow current herbicide label instructions for determining rates of application, necessary surfactants, approved application sites, safety gear, and use precautions. Additional information about the various herbicides used in forestry applications are in Osiecka, Nowak, Long and Mossler, Herbicides registered for pine management in Florida – 2005 update. (http://edis.ifas.ufl.edu/FR158) and Osiecka, Nowak and Long, Primer on chemical vegetation management in Florida pine plantations (http://edis.ifas.ufl.edu/FR160).

Trees/Shrubs

Chinese tallow (Sapium sebiferum)

The Chinese tallow, a.k.a. popcorn tree, was introduced from China in the early 1900s and has since invaded most of the southeastern states. It is a small tree whose seeds are widely dispersed by birds and water runoff. The tree's attractive, light green, heart-shaped leaves that yield bright yellow and orange fall colors have made it a popular ornamental. It is also used by beekeepers for honey production. However, this tree is threatening to become the prominent component of marshes, river margins, and dry uplands within its expanding range. Further planting of this tree is prohibited by the Florida Department of Agriculture and Consumer Services (FDACS), and it is listed as a noxious weed by the U.S. Department of Agriculture (USDA) and the Exotic Pest Plant Council (EPPC).

Control

Herbicide application is required to achieve adequate control of Chinese tallow. It can be cut down but will re-sprout from stumps if not also treated with herbicides. The treatments below will be most effective when applied from late summer to early fall. Follow-up treatments may be necessary in all cases. See Table 1.

Mimosa or silk tree (Albizia julibrissin)

Mimosa is a small to medium-sized tree with attractive, fern-like leaves and showy pink flowers. It vigorously establishes on disturbed areas, often spreading by seed from nearby ornamentals. It was introduced to the United States as an ornamental in 1745 and continues to be used as such because of its attractive form, foliage and flowers. It reproduces both vegetatively and by seed. If cut or top-killed, it will re-sprout quickly, growing 3 feet in a single season. Due to its ability to produce large seed crops and re-sprout when damaged, mimosa is a strong competitor to native trees and shrubs in open areas or forest edges. Dense stands of this tree can significantly reduce sunlight and nutrients available for other plants.

Control

Mimosa can be controlled with the use of mechanical (cutting, chopping, mowing) and chemical treatments. Due to suckers and re-sprouts, chemical treatments are necessary for full control. Basal bark treatments are most effective if applied when seeds are present on the tree, which reduces seed spread. Seedlings up to 10 inches tall can be hand-pulled. See Table 2.

Chinese privet (Ligustrum sinense) Japanese privet (Ligustrum japonicum) glossy privet (Ligustrum lucidum)

These members of the olive family are shade-tolerant, tall, evergreen-leaved shrubs that can grow to about 30 feet in height. They spread by bird-dispersed seeds or underground runners, and form dense stands that prevent pine and hardwood regeneration and/or land access. These plants were introduced from Asia.

Control

Adequate control of these shrubs can be achieved through herbicide application. Often dense thickets of privet need to be cut down or mowed and the sprouts treated with herbicides. See Table 3.

Coral ardisia (Ardisia crenata)

Coral ardisia, or spice ardisia, is an evergreen shrub, 2-6 ft tall, with dark green scallop-margined leaves. Flowers and fruit are produced in axillary, not terminal, clusters, usually drooping below the foliage. Fruit are small, bright red, one-seeded drupes. It was introduced into Florida for ornamental purposes in the early 1900s and has spread and become naturalized in hardwood hammocks across the north part of the state. It does not grow well in full sunlight. Seedlings of native plant species are shaded out where it forms dense thickets of more than 100 plants per square meter.

Control

Adequate control of this plant can be achieved through herbicide application. Seedlings can be hand-pulled. See Table 4.

Vines

Kudzu (Pueraria montana) (=Pueraria lobata)

Although restricted to northern portions of Florida, kudzu is among the worst weed problems for forest managers in the southeastern United States. Kudzu was introduced into the United States at the Philadelphia Centennial Exposition in 1876. By 1900 kudzu was available through mail order as an inexpensive livestock forage, and was later sold by the USDA to be planted for erosion control purposes along rights-of-way and gullies. It now exists in impenetrable patches as large as 100 acres and will overtop and kill trees, even after they are mature. Kudzu is an aggressive leguminous vine capable of growing 1 foot per day. It can easily grow 60 feet in a single growing season. It also establishes roots sporadically as it covers an area, layering vines and foliage on top of each other. One key to this plant's efficiency is its ability to orient each leaf so that the maximum amount of sunlight possible is absorbed. This multidirectional orientation of leaves also poses special problems with sufficiently wetting the top sides of foliage with herbicide.

Control

Special effort is required to control kudzu. The older the patch, the harder it will be to control and the longer it will take to completely eradicate the plant. In severe cases, follow-up spot treatments may be required for 5 to10 years.

It is best to first evaluate the kudzu problem by determining the age of the patch. Do this by looking at the root crowns (the top of the primary root). If the root crowns are 2 inches or larger in diameter, the patch is about 10 years of age or older. In some cases, patches of kudzu greater than 10 years old may require higher concentrations of herbicide for adequate control. For easiest access, it is best to evaluate kudzu problems in winter when vines and foliage are withered.

Due to their potency, Tordon ^TM products are the most effective herbicides for kudzu control. However, the active ingredient - picloram - has a long period of soil activity and the products are not labeled for use in the state of Florida. Acceptable control can be achieved with the use of other herbicides.

Where kudzu is draping trees, a foliar application of Garlon 4^TM, as shown in the table below, provides effective control. If kudzu is in a drain or around open water, Veteran 720 ^TM or Vanquish ^TM, both labeled for ditch banks, is the best choice. Where kudzu invades hardwoods or young pine stands, a broadcast application of Escort ^TM may control the kudzu without harming pines and most hardwoods (with the exception of cottonwoods, elms, and legumes such as redbud or locusts). Transline^TM is specifically formulated to control legumes and other plants. All treatments will likely need to be followed by a second treatment 1 year after the initial treatment. Repeat follow-up treatments until acceptable control is achieved. See Table 5.

Air potato (Dioscorea bulbifera)

This invasive vine from Africa was introduced into Florida in 1905, when a horticulturalist discovered the vine's rapid growth into dense masses. Aside from kudzu, it is the most aggressive invasive vine in Florida. It quickly grows to 60-70 feet in length, high enough to overtop and shade out native trees. The air potato is a member of the yam family and produces many aerial tubers (potato-like growths) called bulbils that are attached to the stems, which eventually fall off and grow into new plants. It is listed as invasive by EPPC.

Control

Begin by collecting all bulbils, if any, from the ground and removing them from the site. Dispose of the bulbils by putting them in a garbage bag and placing it with yard debris for pick-up. Municipalities dispose of them by incinerating them or incorporating them into hard turf. Bear in mind that many bulbils will be underground: either dig them up or apply herbicide to their emergent vines before they can produce more bulbils.

Once this is done, adequate control can be achieved with the use of herbicides. Guidelines for herbicide control are listed below. Follow-up treatments may be necessary in all cases. See Table 6.

Japanese climbing fern (Lygodium japonicum)

Japanese climbing fern is a perennial, delicate looking, climbing vine that forms dense clumps that can cover trees and shrubs. Introduced from Japan as an ornamental, it is scattered throughout the lower portions of Alabama, Georgia, Louisiana, South Carolina and south into central Florida. Further planting of this vine is prohibited by FDACS.

Japanese and Old World climbing ferns are presently the only non-native invasive ferns in the South. At this time, Old World climbing fern is restricted to central and south Florida. Both ferns reproduce readily by wind-blown spores. Animals, equipment and even people that move through an area with climbing fern are also very likely to pick up spores and move them to other locations on the property or even to other properties.

Control

Adequate control of this plant has been achieved with multiple applications of Accord ^TM. Other herbicides have also been used to control Japanese climbing fern. As with most invasive plants, repeated treatments may be necessary. See Table 7.

Grasses

Cogongrass (Imperata cylindrica)

Cogongrass is a fast-growing, rhizomatous, perennial grass that has become one of the most troublesome weeds in non-agricultural areas in Florida. It was accidentally introduced as packing material from Japan in Mobile, Alabama in 1911. It was later intentionally introduced from the Philippines into Mississippi as forage. The Mississippi population was shared with the University of Florida, USDA Plant Introduction Station, and Soil Conservation Service in 1937 for forage and soil stabilization. It has proved to be an excellent soil stabilizer but it is extremely difficult to prevent its escape into unintended areas. It spreads predominantly by wind-blown seeds. Cogongrass is listed as a noxious weed by FDACS and USDA, and it is ranked among the 10 most invasive weeds in the world.

Control

Recommendations to control cogongrass are to treat these infestations in the fall with glyphosate and/or imazapyr herbicides. These recommendations are consistent over a wide range of studies conducted across the South such as Miller (2003) and Faircloth et al. (2005). Fluazifop (Fusilade^TM) is also an effective option. Because of the extensive rhizomes of cogongrass, repeated applications of herbicide are often necessary to maintain some control. Guidelines for herbicide control are shown below. Remember to thoroughly wet the plants with the herbicide mixture when they are green and growing, not during droughts or time of plant stress. Our demonstration areas indicate that successful treatments have been achieved from late May through October. See Table 8.

Bahiagrass (Paspalum notatum) Bermudagrass (Cynodon dactylon) giant fescue (Festuca arundinacea) Johnsongrass (Sorghum halepense)

These grasses have been widely planted and continue to provide forage for livestock, but they can present problems for forest landowners wanting to establish pine stands on sites dominated by them. Introduced as improved pasture grasses from the Mediterranean region of Europe and Africa, they are now distributed worldwide.

Control

Adequate control of these grasses can be achieved with a summer application of Accord^TM followed by a spring application of an Arsenal AC^TM and Oust^TM tank mix. See Table 9.

Conclusion

The invasive exotic species described in this publication represent those most likely to be found in forestlands in north Florida. More complete information on these and other non-native plants can be found in Langeland and Burks' "Identification and Biology of Non-native Plants in Florida's Natural Areas" (1998) and Langeland and Stocker's "Control of Non-native plants in Natural Areas of Florida" (1997). Another good source of information on invasive plants can be found in Miller's “Non-native Invasive Plants of Southern Forests.”

Learn to identify these invasive plants and if they show up on your property treat them quickly before they can expand and increase the difficulty of controlling them. Treated areas should be periodically examined to determine if retreatment is necessary. It is normal for areas infested with invasive plants to receive multiple treatments to effectively reduce the impact and presence of these plants.

References

Anon. Air Potato Dioscorea bulbifera. University of Florida, IFAS, Center for Aquatic and Invasive Plants, Invasive Nonindigenous Plants in Florida. [Online] http://plants.ifas.ufl.edu/diobul.html

Anon. Dioscorea bulbifera L. Florida Exotic Pest Plant Council. [Online] http://www.fleppc.org/

Ezell, A.W. 1998. Effective kudzu control. Mississippi State University Extension Service. 4 p. [Online] http://www.sref.info/publications/print_pubs/pub_505/view

Faircloth, W. H., M. G. Patterson, J. H. Miller and D. H. Teem. 2005. Wanted Dead not Alive: Cogongrass. Alabama A&M and Auburn Universities, Alabama Cooperative Extension publication ANR-1241. 4 p.

Jacono, C.C., and C.P. Boydstun. 1998. Proceedings of the workshop on databases for nonindigenous plants, Gainesville, FL, September 24-25, 1997. (Revised November,1998)

Johnson, K. 1998. Exotic plant species profile: kudzu. Southeast Exotic Pest Plant Council, Nashville, TN.

Jose, S., J. Cox, D.L. Miller, D.G. Shilling, and S. Merritt. 2002. Alien Plant Invasions: The Story of Cogongrass in Southeastern Forests. Journal of Forestry. 100(1): 41-44.

Kline, W.N. and J.G. Duquesnel. 1996. Management of Invasive Exotics with Herbicides in Florida. Down to Earth. 51(2):22-28.

Langeland, K.A. and K.C. Burks. 1998. Identification and biology of Non-native Plants in Florida's Natural Areas. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Pub. No. 257. 166 p.

Langeland, K.A. and R.K. Stocker. 1997. Control of Non-native Plants in Natural Areas of Florida. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. SP 242. 38 p. [Online] http://edis.ifas.ufl.edu/WG209

Langeland, K.A. 1997. Help Protect Florida's Natural Areas from Non-native Invasive Plants. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Circular 1204. 6 p. [Online] http://edis.ifas.ufl.edu/AG108

Miller, J.H. 1999. Controlling exotic plants in your forest. Forest Landowner. 58(2):60-64.

Miller, J.H. 2003. Non-native Invasive Plants of Southern Forests: A Field Guide for Identification and Control. USDA Forest Service, Southern Research Station, General Technical Report SRS-62, Asheville, NC. 93 p.

Muller, R. 1998. Invasion Ecology: the Successful Colonization of Plant Communities by Exotic Species. Natural Resources Newsletter. University of Kentucky College of Agriculture, Cooperative Extension Service. Lexington. 23 p.

Osiecka A., J. Nowak, A. Long, and M. Mossler. 2005. Herbicides Registered for Pine Management in Florida – 2005 Update. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Cir. No. 1475. 24 p http://edis.ifas.ufl.edu/FR158

Remaley, T. 1998. Silk Tree: Albizia julibrissin. Native Plant Conservation Initiative, Alien Plant Working Group. U.S. National Park Service. Gatlinburg, TN. [Online] http://www.nps.gov/plants/alien/fact/alju1.htm

Shilling, D.G. et al. 1997. Ecology, Physiology, and Management of Cogongrass (Imperata cylindrica): Final Report. University of Florida. Gainesville. 128 p.

Westbrooks, R. G. 1998. Invasive plants: Changing the Landscape of America Federal Interagency Committee for the Management of Noxious and Exotic Weeds, Washington, D.C., USA

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy, Interim Dean.

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