Integrated Pest Management Manual
Exotic weeds I
This module is intended to serve as a source of basic information needed to implement an integrated pest management program for kudzu, saltcedar, and Brazilian pepper. Any pest management plan or activity must be formulated within the framework of the management zones where it will be implemented. Full consideration must be given to threatened and endangered species, natural and cultural resources, human health and safety, and the legal mandates of the individual parks. Recommendations in this module must be evaluated and applied in relation to these broader considerations.
This module discusses the biology and management of three
woody or semi- woody exotic weeds--kudzu, saltcedar, and
Brazilian pepper--that are most abundant and damaging in
the mid-Atlantic and southern United States. Due to their
aggressive growth habits, these weeds outcompete and displace
native plants. In addition they overgrow and damage structures,
impede waterways, and may have direct toxic effects on animals.
The management objectives for these three weeds differ according
to the use of the affected land area, and range from local
elimination of small or newly-established infestations to
reductions of well-established populations to tolerable
In some cases exotic vegetation is allowed to remain because it is historically accurate and contributes to the character of a cultural landscape. For example, some introduced species were brought to an area during a certain time period or by a particular group and thus provide important information about the history of a site. Although historically correct, these species can become an immense problem if they are not kept from spreading. Many historic sites have fallen into disrepair, allowing introduced plant species to spread into natural zones and force out native vegetation. Natural resource managers, cultural resource managers, and maintenance personnel must work together to establish priorities for the preservation of historic landscapes that consider protection of both the cultural and natural resource.
IDENTIFICATION AND BIOLOGY OF KUDZU, SALTCEDAR
AND BRAZILIAN PEPPER
A native of Asia, Puearia lobata was introduced into the United States at the Philadelphia Centennial Exposition in 1876. Beginning in 1933, farmers in the South were encouraged to plant kudzu to reduce soil erosion. By 1953, it had become such a weed problem that it was removed from the USDA's list of permissible cover plants. In 1970, the USDA began listing kudzu as a common weed in the south. Today, kudzu is common in Alabama, Georgia, Mississippi, Tennessee, the Carolinas, Kentucky, Virginia, Maryland, and west to Texas and Oklahoma (Edwards 1982). The weed has also been reported in New York, Illinois, Iowa, Nebraska, and Washington (Shurtleff and Aoyagi 1977). It has also been observed at Biscayne and Everglades national parks in Florida.
P. lobata (Willd.) Ohwi is a legume of the subfamily Fabaceae. It is a trailing or climbing semi-woody perennial vine reaching 32'-100' in length. Young vines are covered with soft, fine hairs. First-year vines may reach 1/2" in diameter; old vines may reach a diameter of 4". As many as 30 vines may radiate from a single crown. Vines can grow up to 60' in a single growing season (and reportedly up to 1' per day). Vines may climb vertically as high as 50', completely covering trees, buildings, or other supporting objects. During the growing season, vines are densely covered by foliage. Leaves are alternate and compound, with three broad leaflets up to 4" across, each leaflet entire or deeply two or three lobed and with hairy margins. Foliage drops after the first fall frost. The roots of kudzu are fleshy; the taproot may reach over 6' in length, 7" in diameter, and may weigh up to 400 lbs.
Kudzu plants are perennial and do not usually flower until their third year. Flowers are purple, fragrant, about 1/2" long, produced in long racemes resembling pea flowers in shape. They are produced in August and September. Flowers are followed by flattened, 2" long hairy pods which may contain 3-10 hard seeds. Seeds are rarely produced in the United States (except on plants supported vertically on buildings, trees, or other supports [Shurtleff and Aoyagi, 1977]). In the United States, kudzu generally spreads by means of stolons (runners) and rhizomes. In addition, any vine contacting the soil will produce roots at nodes; these roots enlarge, forming new crowns. Vine cuttings and root divisions will also sprout. Vine nodes that come in contact with soil root to establish new plants; these roots produce new crowns, and the connection to the mother crown dies within one year after rooting. Kudzu is deciduous; its leaves drop after the first frost, and new leaves are produced each spring. See Shurtleff and Aoyagi (1977) or other weed atlases for drawings of kudzu.
Kudzu grows well under a wide range of environmental conditions, although best growth is achieved where winters are mild (40o-60 oF), summer temperatures rise to about 80oF, and rainfall is abundant (40" or more). Kudzu can grow in nearly any type of soil (e.g., acid soils, lime soils, lowlands with high water tables, and over heavy subsoil), and where winter soil temperatures remain above -25oF (lethal temperature for roots). Forest edges or disturbed areas such as abandoned fields and roadsides are preferred habitats. Vines are intolerant of shade and grow toward light. Large roots store water, allowing plants to survive in fairly dry climates (to 20" of rain per year). Growth is most rapid in acid to neutral soils (pH 4.5-7.0).
Kudzu grows rapidly, choking out competing vegetation in sunny areas. Climbing vines may completely cover and shade out trees, and may cover and damage buildings, overhead wires, and other structures.
This term includes Tamarix spp., especially T. ramosissima (Ledeb.), which is generally (but incorrectly) known as T. pentandra (Baum 1978). Saltcedar is a native of Eurasia and Africa, was introduced into the United States as an ornamental shrub in the early 1800s, and has now spread throughout the inter-mountain region of the western United States (Carman and Brotherson 1982). Saltcedar is considered beneficial in that it provides good nesting habitat for wildlife (including doves) and is an excellent source of nectar for honeybees in Arizona and New Mexico (Deloach 1989).
Saltcedar is a deciduous shrub or small tree growing to 12'-15' in height. Slender, long gray-green branches are spreading or upright, often forming dense thickets. Scalelike leaves are gray-green, alternately arranged, narrow, pointed, about 1/16" long, and overlap one another on the stems. Active growth occurs from early or mid-spring to fall, when leaves drop. Leaves often become encrusted with salt secretions. Branches take on a brown-purple color as they age. Bark is reddish-brown and smooth on young branches, becoming ridged and furrowed on older limbs. Large numbers of pink to white flowers, about 1/16" across, appear in a dense mass on 1/2"- 2" spikes at branch tips from March to September. Flowers are pollinated by bees and other insects and produce greenish-yellow to pinkish-red capsules, 1/8"-1/5" long, which split into three to five parts on maturity. Seeds are 1/25" long, with a tuft of fine hairs at one end. The number of seeds per capsule is not constant. Seeds are dispersed by wind to new locations. Seedlings require extended periods of soil saturation for establishment. See Baum (1978) or Parker (1972) for drawings of saltcedar.
Saltcedar occurs in moist rangeland and pastures, bottomlands, banks, and drainage washes of natural or artificial waterbodies, and in other areas where seedlings can be exposed to extended periods of saturated soil conditions for establishment. Saltcedar can grow on soils with up to 15,000 ppm soluble salt. Established plants have long roots that can tap deep water tables. Furthermore, saltcedar has the highest known evapotranspiration rate of any desert phreatophyte (Carman and Brotherson 1982), which may result in water depletion from the underlying soil.
Among the serious direct impacts of this species are the displacement of native range plants by its aggressive growth, the possibly serious depletion of ground water due to its rapid evapotranspiration rate, increased deposition of sediments in tamarisk- infested streams, and the blockage of streams and artificial water channels by dense clumps of saltcedar growth, which can promote flooding during periods of heavy rain.
Brazilian pepper (Schinus terebrinthifolius [Raddi]) is a member of the Anacardiaceae, and is closely related to poison ivy. This weed was introduced from its native Brazil in 1898 by a USDA plant explorer (Morton 1978). It was considered an ornamental shrub and was distributed by the USDA Plant Introduction Station in Miami, FL, to local plant enthusiasts. Since then, Brazilian pepper has spread over thousands of acres of land in south and central Florida, the Florida Keys, the Hawaiian Islands, southern Arizona, and southern California.
Brazilian pepper is a broad-topped, rapidly-growing, evergreen tree reaching up to 40' tall, with a short trunk up to 40" thick. The trunk is usually hidden by a dense head of intertwining, contorted branches. Leaves are evergreen, pinnate, and have reddish midribs which may be winged. Each leaf bears 3-13 sessile, oblong or elliptical, finely toothed, glossy, resinous, aromatic 1-2" leaflets. These are dark green on the top and lighter on the underside. Five-petaled, white, 1/8" flowers are borne in 6" sprays originating in leaf axils along the upper 32"-43" of each stem. Male and female flowers are borne on separate trees. Flowering peaks in October in Florida. Blooms are followed by masses of round single-seeded drupes, which change from green to bright red at maturity. The appearance of the fruit is responsible for the common names "Florida holly" and "Christmas berry." Seeds may be dispersed by birds or small mammals or may germinate near the parent plant, producing dense spreading colonies. See Olmsted and Yates (1984) for photographs of Brazilian pepper.
This tree quickly colonizes disturbed areas. Seedlings can tolerate low light levels, growing slowly until the overstory canopy is opened up. Dead trees should be allowed to remain in the canopy to provide as much shade as possible. Seedling survival is low on inundated ground. Trees can withstand extended drought, and up to six months of inundation. Large trees can withstand fires and high winds without suffering significant damage (Olmsted and Yates 1984). Apparently, Brazilian pepper can tolerate Mediterranean, tropical, and desert climates.
Direct negative environmental impacts include the displacement of native plants, not only because of this species' aggressive, rapid growth, but also because of allelopathic effects (toxic or inhibitory activity) of chemicals in vegetative plant parts and fruits. Brazilian pepper is closely related to poison ivy and can produce effects similar to that plant on humans and animals (Lloyd et al. 1977; Morton 1978; Olmsted and Yates 1984). Massive bird kills in Florida may have been caused by excessive feeding on Brazilian pepper berries.
MONITORING AND THRESHOLDS
Regular monitoring of both developed and natural areas is required to determine the presence and extent of kudzu incursions. Since this species is a rapid grower and an aggressive competitor, these inspections should be conducted frequently (at least monthly) during the growing season.
In addition to inspecting areas for actively growing kudzu, monitors should also inspect disturbed areas, which can be rapidly colonized by the weed. All records of sightings of kudzu and of disturbed sites should be recorded, maintained, and updated at each inspection.
Since this weed is an adaptable, aggressive competitor that can rapidly overgrow native vegetation, the presence of any kudzu should trigger control activities. There is no acceptable population level (L.K. Thomas, Jr., personal communication).
Inspection of both developed and natural areas is necessary to determine the presence and extent of saltcedar incursions. One inspection should be made early in the growing season (before or at flowering), to identify mature plants and initiate control before seed can be set and distributed. Additional inspections should be made later in the growing season to identify seedlings developing from seed set in the current year. All records should be maintained and updated at each inspection.
The presence of any saltcedar should trigger control activities, although it should be recognized that where stands are extensive, elimination is probably infeasible (P. Sanchez, personal communication).
Inspection of all likely habitats is required to determine the presence and extent of Brazilian pepper incursions. At least one inspection per year should be made for the presence of established plants. Frequent inspections (at least monthly) should be made for the presence of disturbances in the normal plant cover (e.g., due to storms, alterations of water levels, fires, and human activities), since such sites can be rapidly colonized by this weed. All records should be maintained and updated at each inspection.
The presence of any plants should trigger control activities, since this species is capable of displacing native vegetation.
Cutting. Vines (including runners) are chopped just above ground level and the pieces destroyed by burning or feeding to livestock. Early in the season, cutting is repeated at two-week intervals to weaken the crown and prevent resumption of photosynthesis. Later in the season, when the stored energy in the taproot has been reduced, the interval between cuttings can be extended (L.K. Thomas, Jr., personal communication). Cutting does not affect roots or crowns, which will regrow unless their supply of stored energy is depleted.
Flaming. A kerosene torch is played over the foliage, wilting the leaves and defoliating the plant. Flaming should be done according to the same schedule as cutting. Where all foliage can be reached, this method may be more effective than cutting. Like cutting, flaming does not affect the roots or crowns.
Burning. Destroys above-ground growth. Since kudzu vines usually will not burn during growth (because of their high water content), vines may be flamed (see above) two or three days prior to burning. This causes the leaves to wilt and dry, providing fuel for the burning process.
Grubbing. This consists of mechanical removal and destruction of the entire plant, including the taproot. If all root tissue is removed, no regrowth can occur, so repetition should not be necessary. However, this procedure can be destructive to the treated area. Removal of crowns only is more effective than cutting, but must be repeated, since remaining roots will re-sprout. Crown removal is most effective at flowering (when the plants are weakest) or in the fall. However, the crowns are difficult to find except in the spring, when the operation will be less effective.
Grazing. Kudzu is a favored food of goats and cows, which can provide useful levels of control. Where these can be accommodated in the park management plan, this technique can be effective.
Cutting. This process involves removal of all growth at ground level, but regrowth is not prevented.
Burning. This removes above-ground growth, but allows remaining roots and crowns to re-sprout.
Grubbing. Grubbing with a grubber blade, which is smaller than a root plow, is used to remove smaller stands. This is less destructive than root plowing.
Root pulling. Removal of the main portion of the root system and crown is labor and time intensive. Regrowth from incompletely-removed roots may occur.
Chaining. A chain, 360'-400' long, and weighing 40-50 lb/ft., can be doubled and pulled between two crawler tractors. Chaining may uproot whole plants or may shear trunks at ground level. Drawbacks of chaining include the failure to remove all below-ground tissue, allowing regrowth as well as the destructiveness of the procedure itself.
Root plowing. This process shears vegetation below the ground surface. The root plow kills medium to large shrubs by shearing below the crown, largely (but not completely) preventing regrowth. This technique is destructive to the environment but is widely used in areas where saltcedar coverage is nearly 100% (Gangstad 1982).
Drag lining. Drag lines are used to shear vegetation growing in water bodies or channel banks. It is not suitable for large vegetation.
Bulldozing. This shears plants at ground level, or uproots entire plants. Regrowth from sheared trunks can occur. This, also, is a destructive technique.
Inundation. Flooding can be used to control saltcedar growing on lake shores if root crowns can be flooded for at least three months (DeLoach 1989).
Hand removal. Seedlings or small saplings can be pulled from the soil. Pulled plants must be removed from their growing site and bagged or dried to prevent re- sprouting.
Burning. Olmsted and Yates (1984) report that prescribed burning has kept a slash pine forest in Florida free of Brazilian pepper seedlings.
Bulldozing. This technique has been used in the Everglades National Park (Olmsted and Yates 1984).
In the United States, kudzu vines may be attacked by a root knot nematode (Meloidogyne sp.), a "blackleg" fungus disease, a viral mosaic disease, and a rust fungus (Shurtleff and Aoyagi 1977). These pests produce only minor injury and are not known to kill kudzu plants.
Watts et al. (1977) found only a few native insects that fed on saltcedar in New Mexico. These did little harm to the plants except under exceptional circumstances. Aphids, grasshoppers, beetles, and spider mites were among the organisms found. Watts et al. also reported two introduced insects, the leafhopper Opsius stactogalus and the scale insect Chionaspis etrusca, were found regularly on saltcedar. The leafhopper sometimes caused substantial damage. Baum (1978) compiled a list of insects and fungi that attack various species of Tamarix in Europe, Africa, and Asia, but found no records of enemies of T. ramosissima. Deloach (1989) recently reviewed the prospects for biological control of saltcedar and suggested that through the importation of several biological control agents from Asia and other areas, control of this weed could approach 80%.
Goats can graze on foliage of this species without suffering ill effects (Morton 1978). A witches' broom disease fungus, Sphaeropsis tumefaciens Hedges, attacks Brazilian pepper, but is also a pest of Ilex opaca, Citrus spp., and numerous ornamentals. The red-banded thrips (Selenothrips rubrocinctus Giard.) occasionally kills plants, but is also a pest of mango and cashew plantings. Recently, Bennett et al. (1989) reviewed the status of biological control activities directed against Brazilian pepper. Three species of insects were recently imported to Hawaii from South America for the control of Brazilian pepper. A bruchid beetle, Bruchus atronotatus, and a tortricid moth, Episimus utilis, established on the weed but caused no significant population reductions. A gelechiid moth, Crasimorpha infuscata, apparently failed to establish (Bennett et al. 1898).
Several herbicides have been used to manage the weeds described in this module. These will not be described in detail, since new herbicides are constantly being developed. Contact your regional Integrated Pest Management coordinator for information on the most appropriate materials to use in your situation.
Several herbicides have been successfully used in the National Park Service to manage kudzu. These projects are described in Bratton (1981), Rosen (1982), and Gangstad (1989). Cut stump treatments have been effective at Great Smoky Mountains National Park. These work best on small infestations or after foliar treatments the previous season.
A variety of herbicides have been used to manage saltcedar. These are generally applied as cut-stump treatments, although foliar, stem-sprout, root-sprout, injection, frill, and broadcast applications are used as well. When cut-stump treatments are used, the herbicide should be in a non-evaporative base so that the stump does not dry out before the chemical has entered. Deloach (1989) has reported on successful use of this technique. Gangstad (1989) has also described several methods for chemical control of saltcedar.
Non-woody seedlings can be treated with foliar applications. Small woody saplings and established trees can be treated with a spray to every major stem (complete coverage to runoff, at 12"-15" above ground level). Treated sites should be monitored and surviving trees retreated at six week intervals following treatment, until regrowth no longer occurs. Gangstad (1989) described a technique for management of Brazilian pepper in rangeland and permanent pastures.
Regular cutting (or flaming, where applicable) may be sufficient to control most kudzu populations. Grubbing may control small infestations, if it will not result in too much destruction of other vegetation. Where it can be accommodated, grazing by goats may preclude the need for additional measures. For large overgrown areas, application of a recommended pesticide may be necessary.
Individual plants can be grubbed from the soil. Cutting followed immediately by application of herbicide to stump ends is the most effective means of controlling small stands of mature shrubs.
Small trees or individual seedlings can probably be mechanically pulled by workers wearing protective clothing. Prescribed burns may prevent establishment of seedlings in appropriate circumstances. Cutting and bulldozing may be useful against large trees and stands. Seedling stands and established trees may be treated with registered herbicides.
1. Baum, B.R. 1978. The genus Tamarix. The Israel Academy of Sciences and Humanities, Jerusalem.
2. Bennett, F.D., L. Crestana, D.H. Habeck, and E. Berti-Filho. 1989. Brazilian peppertree - prospects for biological control. pp. 293-297. In: Proceedings VII International Symposium on Biological Control of Weeds. E.S. Delfosse (ed.).
3. Bratton, S. 1981. The experimental kudzu control program at Chicamauga- Chattanooga National Military Park and Cumberland Gap National Historic Park. Scientific Project Summary. NPS: 542-8301.
4. Carman, J.G., and J.D. Brotherson. 1982. Comparisons of sites infested and not infested with saltcedar and russian olive. Weed Science 30:360-364.
5. DeLoach, J.C. 1989. Prospects for biological control of saltcedar (Tamarix spp.) in riparian habitats of the southwestern United States. pp 307-314. In: Proceedings VII International Symposium on Biological Control of Weeds. E.F. Delfosse (ed.).
6. Edwards, M.B. 1982. Kudzu--ecological friend or foe. Proc. Southern Weed Sci. Soc. Ann. Meeting 35:232-236.
7. Gangstadt, E.O., Ed. 1982. Weed control methods for rights-of-way management. CRC Press, Inc., Boca Raton, FL.
8. Gangstadt, E.O. 1989. Woody brush control. CRC Press. Boca Raton, FL.
9. Lloyd, H.A., M. Taysir, M. Jauni, S.L. Evans, and J.F. Morton. 1977. Terpenes of Schinus terebrinthifolius. Phytochemistry 16:1301-1302.
10. Morton, J.F. 1978. Brazilian pepper--its impact on people, animals, and the environment. Economic Botany 32:353-359.
11. Olmsted, I., and S. Yates. 1984. Florida's pepper problem. Garden, May/June 1984. pp. 20-23.
12. Rosen, A. 1982. Chapter III. Herbicide treatments. Feasibility study: Eradication of kudzu with herbicides and revegetation with native tree species in two National Parks. M.S. Thesis, University of Tennessee.
13. Shurtleff, W., and A. Aoyagi. 1977. The book of kudzu. Autumn Press, Los Angeles, CA.
14. Watts, J.G., D.R. Liesner, and D.L. Lindsey. 1977. Saltcedar--a potential target for biological control. New Mexico State University Agricultural Experiment Station Bulletin 650.
L.K. Thomas, Jr.
Center for Urban Ecology
National Capital Region
National Park Service
Haleakala National Park
National Park Service