Southeastern United States; on the lower slopes of the Appalachian
Mountains, with separate outliers north along the slopes and forest edges
of southern Illinois, Indiana, and Missouri
Black locust is a fast growing
tree that can reach 40 to 100 feet in height at maturity. While the
bark of young saplings is smooth and green, mature trees can be distinguished
by bark that is dark brown and deeply furrowed, with flat-topped ridges. Seedlings
and sprouts grow rapidly and are easily identified by long paired thorns. Leaves
of black locust alternate along stems and are composed of seven to twenty
one smaller leaf segments called leaflets. Leaflets are oval to rounded
in outline, dark green above and pale beneath. Fragrant white flowers
appear in drooping clusters in May and June and have a yellow blotch on the
uppermost petal. Fruit pods are smooth, 2 to 4 inches long, and contain
4 to 8 seeds. Two other locusts native to the Appalachians, Robinia
viscosa (with pink flowers), and Robinia hispida (with rose-purple
flowers), are used in cultivation and may share black locust’s invasive tendencies.
Black locust poses
a serious threat to native vegetation in dry and sand prairies, oak savannas
and upland forest edges, outside of its historic North American range. Native
North American prairie and savanna ecosystems have been greatly reduced in
size and are now represented by endangered ecosystem fragments. Once
introduced to an area, black locust expands readily into areas where their
shade reduces competition from other (sun-loving) plants. Dense clones
of locust create shaded islands with little ground vegetation. Lack
of ground fuel limits the use of fire in natural disturbance regimes. The
large, fragrant blossoms of black locust compete with native plants for pollinating
IN THE UNITED STATES
Black locust has been planted in many temperate
climates and is naturalized throughout the United
States, within and outside of its historical range, and in some parts
HABITAT IN THE UNITED STATES
is an early successional plant, preferring full sun, well drained soils and
little competition. It is commonly found in disturbed areas such as
old fields, degraded woods, and roadsides. Due to its rapid growth,
black locust has been promoted by state and federal agencies and nurseries,
and is sometimes planted in or near prairies, oak savannas and native woodland
Black locust has been planted
extensively for its nitrogen fixing abilities, as a source of nectar for
honeybees, and for fenceposts and hardwood lumber. The clonal pattern
of growth and connected roots are promoted for erosion control. It
is also used for mine soil reclamation. Black locust is susceptible
to some damage from two native insects, the locust borer (Megacyllene
robiniae) and the locust leafminer (Odontota dorsalis).
BIOLOGY & SPREAD
locust reproduces vigorously by root suckering and stump sprouting to form
groves (or clones) of trees interconnected by a common fibrous root system. Physical
damage to roots and stems increases suckering and sprouting, making control
difficult. Black locust clones easily spread in quality and restorable
natural areas. Although black locust produces abundant seeds, they seldom
Mowing and burning
are only effective in reducing the further spread of young shoots from a
clone or parent tree. To kill a clone, cutting alone is ineffective. Herbicides
applied to the stems or cut stumps spread into the root system and provide
better control. From mid-June to August hand sprayer application of
6.25% glyphosate solution (15:1 water:glyphosate) to stumps cut near the
ground has been used by the Minnesota Department of Natural Resources, Region
V State Parks Resource Management Office. Resprouting and suckering
from dense clones may require follow up treatment after a few years*.
*Because plants that appear
to have been killed can resprout even several years after treatment
with herbicide, annual monitoring should be conducted and follow-up
treatments made as needed.
Throughout the year a 25% triclopyr solution
in basal oil (3:1 oil:triclopyr) applied immediately to cut stumps using
backpack sprayers has been used with success by the Scientific and Natural
Areas Program in Minnesota. Thoroughly wet the cut stump and bark below
the cut, down to the root collar, but avoid runoff. Any runoff will
kill surrounding vegetation, especially if treated in the winter before snow
USE PESTICIDES WISELY: ALWAYS READ THE ENTIRE PESTICIDE LABEL CAREFULLY, FOLLOW ALL MIXING AND APPLICATION INSTRUCTIONS AND WEAR ALL RECOMMENDED PERSONAL PROTECTIVE GEAR AND CLOTHING. CONTACT YOUR STATE DEPARTMENT OF AGRICULTURE FOR ANY ADDITIONAL PESTICIDE USE REQUIREMENTS, RESTRICTIONS OR RECOMMENDATIONS.
NOTICE: MENTION OF PESTICIDE PRODUCTS ON THIS WEB SITE DOES NOT CONSTITUTE ENDORSEMENT OF ANY MATERIAL.
SUGGESTED ALTERNATIVE PLANTS
control, soil enrichment, and nectar sources, plant native grasses and other
native herbs, shrubs and trees that are appropriate for your soil and moisture
conditions. If tree plantings will affect nearby natural communities,
plant oak tree species native to your area for timber or shade. Contact the
native plant society in your state or a state forester or resource manager
for recommendations on appropriate, non-invasive native tree and shrub species
for your site.
Susan Wieseler, Minnesota Department of Natural
Resources, Rochester, MN
Jil M. Swearingen, National Park Service,
Larry Morse, The Nature Conservancy, Arlington,
John M. Randall, The Nature Conservancy, Davis,
Converse, C. 1985. Element Stewardship Abstract
for Robinia pseudoacacia. The Nature Conservancy.
Heim, J. 1990. Illinois Nature Preserves Commission
Vegetation Management Guideline on Black Locust. Illinois Nature Preserve
Commission, Springfield, IL.
Swearingen, J. 2009. WeedUS Database of Plants Invading Natural Areas in the United States: Black Locust (Robinia pseudoacacia). http://www.invasive.org/weedus/subject.html?sub=3350.
The Nature Conservancy. Black
Locust: Element Stewardship Abstract. In: Wildland Weeds Management & Research
Program, Weeds on the Web.
USDA, NRCS. 2009. The PLANTS Database (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
Plant Conservation Alliance, Alien Plant Working Group.