Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org, Japanese barberry, Berberis thunbergii, Infestation
It was introduced in the United States as an ornamental plant. However, like many invasive species, it escaped from managed care and is now naturalized. This plant can dominate deep in the woods and along woodland edges. This crowds out native plants and disrupts these ecosystems. Research has shown that the presence of the black-legged tick, which transmits Lyme disease, increases in areas with dense barberry.
Japanese barberry has small, oval, alternate leaves. Foliage is green to a dark reddish purple. The stems have single spines along their length. Barberry is a very dense plant due to the multitude of small twigs and branches. Small, yellow flowers are produced during the spring, but are not particularly noticeable since they are under the foliage. Red fruit develops and can persist into winter. Birds and other animals feed on the fruit and then deposit seeds as they move.
Young plants can be removed by hand, but this option is not going to work on well-established plants. Gloves are necessary due to the presence of spines on the twigs. Mowing is an option for barberry, but requires professional power equipment. Established plants, even small ones, are not going to be cut using a lawnmower. Plants need to be mowed multiple times each year (3-6 times) to deplete energy reserves and kill the plant.
Barberry can also be pulled out (a weed wrench is a great tool) or dug out, but follow up treatments may be necessary if runners start new plants. Dicamba, 2,4-D, or triclopyr can be applied as foliar herbicides early in the growing season. In late August or early September, glyphosate or triclopyr can be applied as cut stump/branch treatments, or basal bark. Glyphosate can also be applied as a foliar treatment in late summer. Remember to always read the label for specific application sites, precautions and mix rates.