Black locust, a nitrogen-fixing member of the legume family, is a large deciduous tree with thorn-covered branches that grows up to 25 m (80 ft) tall. Leaves are alternate, compound and have 7 to 19 leaflets. Fragrant, drooping white flowers have a yellow blotch on the uppermost petal. Flowering occurs from May to June followed by development of a 3-4 inch long reddish seedpod. Reproduction of black locust is primarily vegetative by means of root suckering and stump sprouting. Black locust grows very rapidly – growth can average 4 ft or more per year. It forms large stands in disturbed woods or open areas and displaces native vegetation. Although black locust is native to parts of North America, it is not native to New England.
Non-chemical control of black locust is largely ineffective because of the plant’s vigorous re-sprouting ability. Cutting or burning generally increases sucker and sprout productivity. Most management efforts have concentrated on use of chemical controls. However, seedlings may be hand pulled if the entire root is removed. Repeated cutting or mowing may achieve some level of control but likely will not result in eradication.
Black locust is difficult to control because of extensive suckering from the stump and roots. Triclopyr is more effective than glyphosate on black locust. Where possible, foliar sprays are effective when the leaves are fully expanded. For larger trees, cut down and apply undiluted triclopyr into the freshly cut surfaces of the stump, or girdle the tree and apply undiluted triclopyr into the cut encircling the trunk. Repeated treatments will likely be necessary.
BRUSH-B-GON [triclopyr (8%)]:
Foliar spray: 4 fl. oz./gal
Cut-stump treatment: Undiluted
Carmen, C.K. 1984. Element Stewardship Abstract for Robinia pseudoacacia (Black Locust). The Nature Conservancy. (and references therein)
Randall, J.R. and J. Marinelli (eds.). 1996. Invasive Plants: Weeds of the Global Garden. Brooklyn Botanic Garden publications, Handbook 149.