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Tips from Botanists: Fighting Honeysuckle

02/26/1998

OXFORD, Ohio -- Once it was recommended as an ornamental shrub that attracted wildlife, but today Amur honeysuckle is considered a pest.

The red-berried shrub, first introduced to North America from Asia at the turn of the century, has escaped cultivation and invaded forests, urban parks, abandoned fields and roadsides throughout the Midwest and East.

Landowners dig it out, spray it and chop it down. Park boards sponsor honeysuckle removal days and invite volunteers to help. One state--Illinois--has even banned its sale. David Gorchov, a Miami University botanist, has studied Lonicera maacki for five years. Working with a team of graduate and undergraduate researchers, he's obtaining answers as to its impact on the environment and how to get rid of it.

The best removal method is to chop or dig out the shrub's crown (the stems and the burl, which is partially buried underground). "If the crown is removed--and the easiest way is with an axe--it is 100 percent effective," Gorchov said. "The plant doesn't sprout back from the roots."

Just cutting the stems of the plant to the ground--even if done repeatedly--does not kill honeysuckle. However, if

the stems are cut and the crown is then painted with herbicide, 66 percent of the plants die. Spraying a herbicide such as Roundup on uncut plants killed 38 percent of the honeysuckle, but also destroyed nearby desirable plants.

Why remove Lonicera maacki ?

"In many forests, this particular honeysuckle forms a nearly continuous shrub layer. Many people suspect that it's having a negative impact on forest plants," Gorchov said.

Because honeysuckle leafs out earlier than native woody plants--almost six weeks before the forest canopy--it shades spring wildflowers during the time they must carry out most of their annual photosynthesis.

A long-term goal is to understand why Lonicera maacki and a handful of other introduced species such as multiflora rose and garlic mustard are so successful that they've become a threat to native plants communities. "If we could predict which species would become a problem, we might be able to prevent their introduction," Gorchov said.

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