Nov 12, 2018

A Sweet Invader

Honeysuckle offer a pleasing scent, but pose dangers to the native ecosystem

By Lawanda Jungwirth

Who doesn’t adore the sweet smell of honeysuckle? There is nothing more delightful than walking down a trail perfumed with honeysuckle in early June.

However, behind the sweetness lurks a wicked invader. Those fragrant swaths of honeysuckle are unfortunately growing quickly larger and destroying all kinds of good things in their paths.

There are many types of honeysuckle including both bushes and vines. Four of the bush types are listed in the Wisconsin Department of Natural Resource’s invasive species Rule NR40. The four bad guys are Amur honeysuckle (Lonicera maackii), Bell’s honeysuckle (Lonicera x bella), Morrow’s honeysuckle (Lonicera morrowii) and Tartarian honeysuckle (Lonicera tatarica).

All four are considered “Restricted” under NR40, and in addition, Amur honeysuckle is “Prohibited” in the area north of a line drawn from Oconto in the northeast part of the state to La Crosse in the southwest. As a reminder, you are not allowed to buy, sell, transport, introduce or possess prohibited species. You are allowed to possess restricted species, but are strongly encouraged to eradicate them.

Notable appearance

I could spend a lot of time here describing the minor differences between the four honeysuckles listed in NR40, but it doesn’t really matter which type a particular one is – they’re all bad. In general though, they are dense, multi-stemmed shrubs between six and 20 feet tall.

Older stems sometimes have shaggy, peeling bark and are often hollow. Leaves are present both earlier and later than those of native shrubs, are green or blue-green, oval in shape with no lobes or teeth and grow opposite each other along the stems. Flowers which may be white, yellow, pink or dark red, are tubular in shape and grow from the leaf axils – the spot where the leaf attaches to the stem. Honeysuckles are prodigious seed producers. The round berries are yellow, orange or red and appear in early July. Each berry contains numerous seeds and they remain on the plants late into winter. Roots are shallow and fibrous, extending from a woody crown.

One notable feature often found on honeysuckles are “witch’s broom” at the tips of the stems. The broom is caused by an insect called an aphid that injects toxins into the stems while feeding. The toxins stunt new growth and distort the growing tips and leaves making the broom.

Invasive honeysuckles are found at forest edges, in open woods, fens, bogs, lakeshores, utility right-of-ways, roadsides, trail sides, pastures and old fields. They are common in urban areas, since they have been and are still marketed as ornamental landscape plants. The problem comes when these ornamentals produce their copious amounts of seeds which birds feast upon. The birds fly off to poop the seeds out in natural areas where they easily germinate.

The honeysuckles then destroy the native ecosystem by decreasing light availability, depleting soil moisture and nutrients, and releasing chemicals into the soil that inhibit the growth of other plants. What’s a native plant to do when faced with that triple whammy?

When I was doing research for this article, I came across the new-to-me phrase “hybrid swarm.” This is a population of hybrid plants that has survived beyond the initial hybrid generation, with interbreeding between hybrid individuals and backcrossing with its parent types. Yup, honeysuckles do this. The hybrid swarm aspect along with their ability to thrive in a wide range of light and soil conditions makes it no surprise that honeysuckles are so successful in overtaking everything in their path.

Taking control

There are four ways to control invasive bush honeysuckles.

The first is mechanically. Bushes can be pulled up by hand when they are young and small – or if a little larger – with the use of a leverage tool. It is easy to pull them in spring or when the soil is wet after a good rain. If plants are fruiting when they are pulled, avoid moving the plants offsite unless you can transport them without dropping fruit. The area will need to be re-checked annually to remove new plants and any that have sprouted from broken root pieces.

The second control method is by doing a prescribed burn in spring. This isn’t something you should attempt yourself without training and must be done for several consecutive years. A little less dangerous, a hand-held propane torch is effective in killing seedlings. No training is needed, but don’t try it if the area has dry leaves or long grass.

The third method is by repeated mowing to within two inches of the ground when plants are young. The best time to mow is immediately after leaf or flower formation. Mowing encourages re-sprouting, so re-mowing or herbicide application later in the season will be needed. It may take several years for mowing to be effective.

The final control method is by herbicide application. There are quite a few different chemicals that can be used and several methods of application. Instead of going into all of them here, I’ll refer you to this University of Wisconsin-Extension publication which lays them all out:  http://learningstore.uwex.edu/Assets/pdfs/A3924-03.pdf. Please pay special attention to the timing of application, don’t apply chemicals on a windy day, don’t use herbicides of any kind near water, and follow all safety precautions.

Lawanda Jungwirth grew up in Omro, Wis. and lives along the Fox River at Rivermoor with her husband, Ron. She has been a University of Wisconsin-Extension Master Gardener since 1994 and writes a gardening column for the Oshkosh Northwestern. She is interested in environmental issues, organic gardening, control of invasive plants, natural health and quilting. Email ljungwirth@charter.net.