Now is time to identify, remove invasive buckthorn and honeysuckle

Source: Wisconsin DNR website

MADISON - Late April to early May is an excellent time to identify infestations of two invasive plants that threaten native wildflowers, according to state and private plant conservationists.

Buckthorn and honeysuckle tend to leaf out very early, which is "particularly harmful to native wildflowers," according to Nancy Braker, secretary of the Invasive Plant Association of Wisconsin and agency relations director with The Nature Conservancy, "because they leaf out earlier than natives, stealing the sunshine." However, she adds, this trait also makes both buckthorn and honeysuckle easier to identify at this time of year.

"If the plants are small enough, early spring is a good time to hand-pull or dig honeysuckle and buckthorn, but the most effective control is an appropriate herbicide applied to cut stumps in the late summer or early fall," Braker says. "Now is a good opportunity to find if they are present in yards or woodlots and prepare for what will need to be done later."

There are two invasive species of buckthorn: common buckthorn (Rhamnus cathartica) and glossy buckthorn (Rhamnus frangula). Both of these are tree-like shrubs that can reach 20-25 feet in height. Both types of buckthorn can be identified by their leaves: common buckthorn has small, dull oval shaped leaves with slightly serrated edges, and glossy buckthorn has similar leaves with a shiny upper-leaf surface and no serrations. Both types of buckthorn are well-established in parts of Wisconsin and compete with native flora.

Honeysuckle is also a shrub that grows 3 to 10 feet tall with oval or oblong leaves and showy, fragrant flowers. Leaf development generally begins two weeks before that of native trees and shrubs. As noted by Braker, the early leaf development of honeysuckle and buckthorn plants is detrimental to native wildflowers that have evolved to bloom before other plants' leaves emerge.

The most effective way to control large buckthorn and honeysuckle invasions is to monitor the infestation through the growing season and in late summer or early fall, cut the plants off at the base, followed by application of an appropriate herbicide. Herbicide application to the cut stump in the spring or summer is generally ineffective, and can harm desired plants more than it helps get rid of invasives.

Seedlings of these invaders can be effectively killed with a herbicide application done carefuly in early spring.

By marking sites where buckthorn and honeysuckle have been identified in the spring, land owners can be aware of their situation and be ready to take active controls in the late summer and early fall when methods will be most effective. Land owners should take the time to monitor their property soon and identify whether or not they have an infestation.

For more information on invasive buckthorn and honeysuckle, see the non-native species page of the DNR Web site.