ALEXANDRIA - Buckthorn, a small, shrubby tree, is a nonnative species that has become a big problem in Minnesota's woodlands and wetlands. In 1999, buckthorn was identified as a restricted noxious weed. This means that its sale, transportation or movement is prohibited statewide by the Minnesota Department of Agriculture.

If buckthorn is non-native, how did it get here in the first place? Until the 1930s, it was sold as a popular hedge by our nursery industry. Many older homes still have buckthorn hedges. These prolific, fruit bearing shrubs attract birds that spread the seeds through their droppings. This has allowed large quantities of buckthorn to spread over a wide and diverse area of the state.

Buckthorn out-competes our native plants for nutrients, light and moisture; degrades and threatens the future of wildlife habitat; contributes to erosion of the forest floor; serves as a host to other pests such as soybean aphid; forms an impenetrable layer of vegetation in our natural areas; and lacks natural controls that would curb its growth.

Autumn is a good time to remove buckthorn because it is easy to spot. In the late fall, when native shrubs and trees have lost their leaves, buckthorn will often still have green leaves into December. Do you have buckthorn on your property? It is fairly easy to identify. Buckthorn has egg-shaped leaves that are finely serrated and pointed at the tip. Large, round black berries grow in clusters, the bark is brown and flaky, and twigs often end in sharp, stout thorns.

Cut down all buckthorn trees greater than 3 inches in diameter. Buckthorns of this size produce berries.

Dig out the stumps or treat them with a herbicide. Of the several chemicals that work well, the two most common ones are glyphosate (Roundup) and triclopyr (Brush-B-Gon). Be sure to use chemicals properly, following all label instructions.

Pull up small trees (less than 1 inch) by hand. They do not have strong roots.

Remove seedlings with a hoe.

Replace buckthorn with native species. Some good substitutes for buckthorn are high bush cranberry, nannyberry, chokecherry, grey dogwood, pagoda dogwood, American hazelnut and black chokeberry.

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Until next time, happy gardening!