Chinese elms (Ulmus parvifolia) are weak-limbed trees that invade more desirable tree stands and aggressively absorb moisture and nutrients. As a result, preferred trees and shrubs can be stunted or even killed off. There are several ways to kill the unwanted invaders. The best course of action should be determined based on the size of the Chinese elm.
They Grow Fast
Chinese elms are deciduous trees that grow over 3 feet per year in U.S. Department of Agriculture plant hardiness zones 4 to 9. They commonly top out at 40 to 50 feet but can grow to 70 feet. While they can be attractive shade trees, they are considered an invasive species in many areas within the United States.
Young saplings can be pulled by hand. Simply grab the sapling at the base of the trunk and pull up with slow, steady pressure. Be careful to get all of the roots as new saplings will sprout from pieces of root left in the soil. The best time to hand pull them is shortly after a good rain while the soil is still moist. If rain is not in the forecast, water the saplings to moisten the soil a day or two before pulling them.
Small to Medium Trees
Chinese elms with a trunk diameter of 4 inches or less can be killed by spraying them with an herbicide containing triclopyr. Ideally, the trees should be sprayed in the spring or summer but the herbicide is still effective in the fall. Triclopyr is available in ready-to-use and concentrate formulations. For trees with a trunk diameter of 1 1/2 to 4 inches, combine one-quarter of a gallon of triclopyr concentrate with three-quarters of a gallon of diesel fuel oil. If the tree trunks are smaller than 1 1/2 inches, dilute the triclopyr concentrate at a rate of one part herbicide to five parts diesel. Pour the mixture into a backpack or hand-pump type sprayer that has a small nozzle. Spray the lower 1 foot of tree trunk with the triclopyr mixture until it is completely wet and almost dripping. Be very careful around desirable trees and shrubs. Drifting spray can damage them. Wear protective clothing and do not spray the herbicide on a windy day.
Chinese elms with trunks over 4 inches in diameter can be cut down and killed with triclopyr. The tree should be cut down as close to the ground as possible. The stump should be sprayed with triclopyr to kill it and the roots. Mix one part triclopyr concentrate into five parts vegetable oil or diesel fuel oil or use the ready-to-use triclopyr. Spray the herbicide on the cut stump surface immediately after cutting down the tree.