Problem Horticultural Plants
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Oklahoma Cooperative Extension Service NREM-2895 Problem Horticultural Plants Dwayne Elmore Oklahoma Cooperative Extension Fact Sheets Extension Specialist,Wildlife Ecology and Management are also available on our website at: http://osufacts.okstate.edu Karen Hickman Professor, Rangeland Ecology and Management alternatives can be found. Further, if noticing an invasive plant Kimberly Holmes being sold at a nursery, please inform the manager. Many Former Assistant Extension Specialist, Consumer Horticulture are not aware of the risks associated with certain plant spe- cies. Some of these plants also may be noticed in the home Gardeners are constantly on the lookout for a new and landscape. Recommendations of native alternatives, when interesting plant that might bring beauty and interest to their practical, is given here, although many non-native species landscape. Some of these plants are cultivars of common posing little risk could also be selected. Basic information native plants found across the forests, prairies, shrublands about the plant, its origin, why or how it was introduced into and wetlands of the southern Great Plains. Others come the U.S., basic traits that lead to its invasiveness, and control from foreign shores. Most of the plants encountered in a is discussed, however a complete taxonomic description of plant nursery are benign and can be safely brought into the each plant is not provided. A map of Oklahoma indicating home garden. However, some of them are significant threats counties with known escaped populations also is presented. to the ecological integrity of Oklahoma. These invasive plants Some of the plants in this guide may not have invasive po- not only are a problem for native flora and fauna, they often tential to the entire state because Oklahoma's climate and impact agricultural production, clog waterways and burden soils vary tremendously. Unfortunately, predictions are difficult, landowners with additional costs. This fact sheet is designed thus recommendations of the plants described here should to help you avoid some of these problem plants. While Okla- be avoided statewide. Notice that most of the invasive plants homa has many invasive plants, a few of the species either listed were intentionally introduced. This continues at pres- currently or likely to become significant problems for our state ent. Therefore, it is the responsibility of each gardener to be are discussed here, as well as plants commercially available prudent and judicious in plant material selection. If there are in plant nurseries or from online vendors. Education about specific concerns or questions about a plant, please contact identifying these problem plants is encouraged and suitable the local Oklahoma Cooperative Extension Service educator. Plants add value and interest to landscapes. However, care should be taken to avoid invasive plants that might escape from the home garden. Division of Agricultural Sciences and Natural Resources • Oklahoma State University Alligator Weed Autumn Olive and Russian Olive Alternanthera philoxeroides Elaeagnus umbellata and Elaeagnus angustifolia L. Origin: Native to Parana River area of South America. Origin: southern Europe and Asia. Introduction: First detected in Mobile, Alabama in 1897. Introduction: Introduced in the U.S. in the late 1800s as an Likely introduced unintentionally from ship ballasts. Now ornamental and windbreak plant. Also used for wildlife distributed across the southeastern U.S. and California. cover and food. Russian olive is found across most of Traits: Spreads primarily by adventitious rooting from stem the U.S. except the southeastern states. Autumn olive is nodes and roots. Grows in shallow water. found primarily in the eastern U.S. Effects: Invades agricultural areas, blocking drainage and Traits: Both of these very similar woody plants can form irrigation canals, causing problems on agricultural land. dense thickets and are quick to invade open grasslands. Can impede boat traffic due to excessive growth. Com- Tolerant of various soil types and capable of germinating petes with native aquatic vegetation. Increases water under existing tree cover. Abundant seed producer that loss through transpiration. Ingestion of plant by cattle can is favored by birds, which aids in dispersal. Very fragrant cause photosensitization, skin lesions and liver damage. flowers and thorns on both species. Has small alternate Excessive plant decomposition can lead to water quality oval to lanceolate shaped green or silver-gray leaves. issues. May lead to increased mosquito numbers. Effects: Overcomes native vegetation. Can assist forest Management: Physical removal can be used, but rarely birds in occupying formerly open grasslands. Interferes removes all plant parts. Bare areas may be recolonized. with nutrient cycling and hydrology. These trees also can Approved aquatic herbicides are effective, but generally change fuel loads of wildfires. require multiple applications. Management: Cut and treat the stump with herbicide for the Alternative Plants: Water primrose (Ludwigia repens) – Note most effective control of this vigorous resprouter. this plant is very aggressive and will cover the surface of Alternative Plants: Mexican plum (Prunus mexicana), Ameri- the water similar to alligator weed, but it is native. can beautyberry (Callicarpa americana), Eastern redbud (Cercis canadensis), and Carolina buckthorn (Frangula caroliniana). Photo courtesy Bruce Hoagland Photo courtesy Jeff McMillian NREM-2895-2 Bermudagrass Callery Pear or Bradford Pear Cynodon dactylon Pyrus calleryana Origin: Africa. Origin: China. Introduction: Introduced into the U.S. around 1751, likely Introduction: Introduced to the United States in 1909 as an in contaminated hay. It was recognized as in important attempt to control fire blight of the common pear. It is now turfgrass and livestock forage, and was quickly planted commonly used as an ornamental. widely. Now occurs across the U.S. with the exception of Traits: Medium-sized tree with showy white flowers in early the north-central region. Most invasive in southern U.S. spring, followed by glossy leaves. There are thorned Traits: Creeping herbaceous plant with narrow leaves that and thornless cultivars. Callery Pear is fairly resistant to reproduces primarily by vegetative means. Two types of disease and pests, tolerates a range of environmental shoots; aboveground as stolons, and belowground as conditions, grows rapidly in dense thorny thickets and rhizomes. Both are capable of rooting in the ground and flowers abundantly. Its seeds are readily dispersed by birds. creating new plants as they grow outward from the original Effects: Its rapid growth inhibits late- to middle-stage succes- plant. Bermuda grass is an aggressive invader in Okla- sional native species from growing in disturbed sites. Its homa and is found in most native grasslands statewide. ability to outcompete native species causes a change in Effects: Forms dense sod, making plants highly competitive plant communities. It also creates cover for some wildlife with crops and other grasses for water and soil nutrients. species, which can change a grassland species commu- Dense sod reduces movement and food resources for nity to a woodland community. It is an excellent roosting many ground-dwelling birds. tree for gregarious blackbirds, grackles and starlings, Management: Physical removal for small areas can be effec- which are problematic in urban areas. This plant has in- tive, but is difficult because underground rhizomes often vaded multiple locations in central and eastern Oklahoma. remain. Mulches of black plastic or geotextile landscape Management: As this plant is a resprouting woody plant, fabric can be effective because light is excluded. Grass- herbicides will be needed. Small poorly established trees selective or nonselective herbicide control can be suc- can be sprayed with a foliar herbicide. Larger trees should cessful, but will require multiple applications. be cut and a basal herbicide applied immediately. Alternative Plants: Buffalo grass (Bouteloua dactyloides). Alternative Plants: Eastern redbud (Cercis canadensis), American plum (Prunus americana), Mexican plum (Prunus mexicana), and Carolina buckthorn (Frangula caroliniana). Photo courtesy Dwayne Elmore Photo courtesy Dwayne Photo courtesy Dwayne Elmore Photo courtesy Dwayne NREM-2895-3 Chinese Privet Chinese Wisteria and Japanese Wisteria Ligustrum sinense Wisteria sinensis and Wisteria floribunda Origin: China. Origin: Southeastern China (W. sinensis) and Japan (W. Introduction: Introduced to the U.S. in 1852 as an ornamental floribunda). shrub. It continues to be sold in the horticultural industry Introduction: Introduced to the U.S. in the 1800s as orna- and is found throughout the southeastern U.S. mental plants. Traits: Medium-sized semi-evergreen shrub that grows in Traits: These very similar long-lived vines are vigorous in shade or partial sun. This plant requires fairly moist soil. growth. New vines germinate from seeds or sprouting Has dark green, small, oval, opposite leaves. Capable of rootstocks. The plant grows in dense thickets. both sexual and vegetative reproduction. Effects: Vines twine tightly around host tree trunks, cutting Effects: Difficult to control because of seedbank size, as well through the bark and may eventually damage or kill the as ability to reproduce from root suckers. Seeds are readily host tree. Dying trees create canopy gaps, which allow dispersed by birds. Tends to dominate