Black locust (Robinia pseudoacacia) is an invasive species in California. This tree grows up to 100 feet tall and produces leaf stems with seven to 19 oval-shaped leaflets. At the base of each leaf grows a spine or pair of spines. Black locust has been used in some states to control erosion because of its rapid growth. It prefers well-drained soils and full sun. In addition to its invasive status in California, this tree may also be considered a nuisance by property owners because of its rather large seed pods -- up to 4 inches long -- and thorns.
Black locust is known to sucker quite badly when cut down. Suckers from the root system of a black locust tree may recur for years. This means an unwanted black locust tree cannot be simply removed, and some chemical control is necessary.
Triclopyr is an herbicide commonly applied to the stem of an unwanted woody plant. This chemical is transported throughout the tree through the root system and phloem tissue, effectively poisoning the plant and ultimately causing its death. Note that this chemical has little shelf life and should not be placed in storage after use. Purchase as small a container as possible.
Application of Herbicide
Mix a solution of 15 percent triclopyr and diesel fuel in an herbicide tank and spray gun. Use an ax or hatchet to frill the trunk of the tree just 10 inches above the soil line. Apply this solution to the frilled part of the trunk, wetting it thoroughly. This should be done in the spring, at a time when no rain is forecast for several days. Frilling the tree before applying the herbicide will give the herbicide direct access to the trunk's phloem tissue and ultimately its extensive root system. This will prevent the tree from producing suckers later on. Once the tree has died, the tree should be professionally removed.
Physical and Chemical Controls
Although simply cutting the tree down will not stop the roots from suckering, this can be prevented if the resulting stump is brushed with a solution of 15 percent triclopyr and diesel fuel. Once the stump is dead and the roots have produced no suckers for at least one year, the stump may be removed from the ground by a professional tree removal company.
- Missouri Department of Conservation: Black Locust Control
- California Invasive Plant Control: Invasive Plants of California's Wildland
- AgriLife Extension: Managing Wildlife Habitat Using Individual Plant Treatment
- Backyard Gardener: Killing Woody Plant Stumps
- Ohio State University: Controlling Undesirable Trees, Shrubs, and Vines in Your Woodland
- University of Rhode Island: Fact Sheet: Black Locust
- Jupiterimages/Photos.com/Getty Images