Invasive plant

Winter Work: Invasive Honeysuckle Treatment

Cross-section photo of the brown and hollow pith of the invasive honeysuckle plant.

The pith of invasive honeysuckle, seen here, is brown and hollow. / Photo Credit: Chris Evans, University of Illinois,

By Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh; or 715-492-0391

They may have sweet-sounding names, but Eurasian bush honeysuckles (Lonicera spp.) can bring a bitter taste to your mouth if found in your woodlands.

Originating as horticultural plantings, this group of upright woody shrubs is now widespread in Wisconsin and the upper Midwest.

Invasive honeysuckle shrubs are among the earliest plants to leaf out in the spring and the last to lose their leaves in the fall. This extended growing season allows them to outcompete other plants for nutrients and sunlight, casting dense shade on the forest floor.

Native honeysuckles are also present in Wisconsin. Several identifying characteristics can help you determine if your honeysuckle is a native species or one of the invasive varieties. When in bloom, the flowers of invasive Bell’s, Morrow’s and Tartarian honeysuckles are easily distinguished. Without the blooms, the easiest methods to determine non-native honeysuckle from the native plant include looking for shaggy, peeling gray-brown bark and checking the pith.

The pith (inner tissue of the branches and stems) can be observed by breaking off an older branch. If the pith appears white, the shrub is native honeysuckle. If the pith is brown and hollow, it is likely one of the invasive bush versions.

Winter is a great time to treat invasive honeysuckle shrubs on your property since most other plants have gone dormant for the season. Winter herbicide applications are highly successful on freshly cut stumps, provided snow does not cover the cut surface. Basal bark applications may also be used on snow-free surfaces.

Stump cutting should be followed by herbicide treatments, as vigorous resprouting may occur from shrubs cut in winter but not treated with herbicide. Learn more about invasive honeysuckles and how to manage them on the Bush honeysuckles fact sheet from Renz Weed Science at the University of Wisconsin-Extension.

Keep Invasive Plants Out Of Spring Garden Plans

Photo of the invasive plant Japanese barberry

Originally planted as a garden ornamental, Japanese barberry can quickly escape cultivation and invade Wisconsin’s woodlands. / Photo Credit: Wisconsin DNR

By Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh; or 715-492-0391

While winter is just beginning to creep in on Wisconsin, many gardeners are already thinking ahead to the next spring planting season. While dreaming of spring blooms and designing your next garden or landscape layout, consider invasive plants that may try to weed their way into your plans.

Many invasive plants that are problematic for Wisconsin forests started as garden ornamentals. Although Wisconsin regulates 145 plants under the invasive species rule NR 40 prohibiting their sale, it’s essential to check your selections before purchasing and choose native plants when possible.

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Watch For Rare Fall Garlic Mustard Blooms

Photo of unusual garlic mustard plant flowering in the fall

Have you seen an unusual case of garlic mustard flowering twice in the same season? If so, please send a report to / Photo Credit: Frederick Hengst, Wisconsin DNR

By Mary Bartkowiak, DNR Invasive Plant Program Coordinator, Rhinelander or 715-493-0920

and Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh or 715-492-0391

Typically a biennial plant, garlic mustard blooms in the spring. So, it sounds crazy to find the plant blooming again in October.

Although garlic mustard might be taking advantage of an extended growing season, this second bloom also may be cause for concern — or, at least, careful monitoring.

Wisconsin Department of Natural Resources Tax Law Forestry Specialist Frederick Hengst discovered this “mutant” specimen in early October while on a landowner visit near Wild Rose. The plant appears to have flowered and set seed several months earlier, but then re-flowered on the same stem.

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Fall: Time To Treat Invasive Plants

By Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center; or 715-492-0391

As we move into cooler temperatures, many plants and trees are changing in leaf color and even beginning to drop their leaves. The Wisconsin Department of Natural Resources (DNR) reminds the public that fall is not only a great time to enjoy the changing hues in the woods, but it also presents a good opportunity to spot the invasive plants persisting among them.

As you walk through your woods this month, look for leaves that stay green into late fall, even after all other trees have lost their leaves. These are likely signs of an invasive plant species.
Invasive plants can hold onto their leaves much longer than native plants, taking advantage of late fall sunshine and ensuring they continue to grow and gain ground in the forest after many other plants have already died out or gone dormant for the winter.

Late autumn and even early winter are great times to identify and treat invasive plants. They are easy to see in a sea of downed leaves and dead plants. The absence of living native plants means that treating invasives with chemical herbicides will cause much less collateral damage.

Fall treatment is ideal for woody invasives, as trees and shrubs are busy directing resources to their roots to store them for overwintering, so the natural flow carries the herbicide along to the roots. Spring treatments are often ineffective because the opposite is true: plants are continually pushing resources up and out toward new buds.

When a control method like cut-and-swipe (a common treatment for buckthorn that involves snipping off stems and using a dabber to apply herbicide directly to the cut) is used in spring, it is often ineffective as the herbicide is immediately pushed out of the plant. In fall and winter, the flow of resources changes, making treatment much more effective.

Common invasive plants that can be treated in fall include garlic mustard, non-native honeysuckles and common and glossy buckthorns. Here are some basic identification characteristics and methods of treatment:

Garlic Mustard

Photo of rosettes on a garlic mustard plant. / Photo Credit: Wisconsin DNR

Rosettes on a garlic mustard plant. / Photo Credit: Wisconsin DNR

Though not a woody plant, the basal rosettes (a cluster of leaves at ground level) remain green through the fall and winter and are easy to spot. Garlic mustard looks somewhat like wild ginger or violets due to its kidney-bean shaped leaves. To check, crush a leaf – the leaves of garlic mustard should have a garlic smell when crushed.

If only a few plants are present, they can be hand-pulled and should be destroyed by burning or sending them to a landfill in bags clearly labeled as “Invasive Plants – Approved by Wisconsin DNR for Landfill.” For larger infestations, plants may be cut or torched, or herbicide may be used as recommended in the Control Method section of the Garlic Mustard Fact Sheet.

Non-Native Honeysuckles

Photo of an invasive honeysuckle plant.

Photo of a honeysuckle plant. / Photo Credit: Wisconsin DNR

Non-native honeysuckles can hold their leaves well into winter. They often have a thick canopy of leaves that shades out native plants. While other plants are bare and the honeysuckle still has that thick canopy, it’s a great time to attack and treat it.

There are several types of invasive honeysuckles in Wisconsin. Learn more about each variety as well as control methods on the Management of Bush Honeysuckles fact sheet from the University of Wisconsin-Extension.

Common And Glossy Buckthorn

Photo of a glossy buckthorn shrub covered in berries

A glossy buckthorn shrub covered in berries. Control berry-producing plants first to prevent further spreading. / Photo Credit: Wisconsin DNR.

A common sight in Wisconsin forests, common and glossy buckthorn is also best treated in late fall and early winter. Buckthorn is a multi-stemmed large shrub or small tree that can form an impenetrable understory layer, displacing native vegetation.

Small buckthorn seedlings can be removed by hand. Larger plants should be cut or girdled at the base. Buckthorn can easily re-sprout from cut stumps, so herbicide treatments are often best. Find more information on control methods on the Buckthorns Management Fact sheet.

After treating any invasive plants in the fall, make sure to follow up in spring to check for new growth and seedlings. Controlling invasive plant species almost always requires multiple treatments and monitoring over several seasons.

Avoid Invasives During Fall Recreation

Photo of firewood self-service stand at a Wisconsin state park

Don’t move firewood! Many State Parks and Forests stock firewood right at the campground entrances. Use these stands or other local sources that are no more than 10 miles from your destination to avoid spreading invasive species. / Photo Credit: Wisconsin DNR

Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center; or 715-492-0391

Whether you prefer to enjoy Wisconsin’s beautiful fall weather on a hike, bike, ATV/UTV or on the water, the Wisconsin Department of Natural Resources (DNR) urges those enjoying the outdoors to take a few precautions to avoid bringing invasive plant species along for the ride.

The Wisconsin Council on Forestry has created a set of guidelines titled “Invasive Species Best Management Practices for Outdoor Recreation.” These voluntary guidelines include steps recommended for individuals to minimize the inadvertent spread of invasive species.

Here are a few universal Best Management Practices (BMPs) for outdoor recreation, along with a few examples of these practices in action.

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Not-So-Notorious Native Buckthorn

Photo of alder-leaved buckthorn, a native species in Wisconsin.

The native alder-leaved buckthorn is much smaller than its invasive counterparts and prefers wet areas such as fens. / Photo Credit: Wisconsin DNR

By Mary Bartkowiak, DNR Invasive Plant Program Coordinator, Rhinelander Service Center; or 715-493-0920
and Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center; or 715-492-0391

Most of the rather frequent buzz about buckthorn revolves around the two non-native, invasive types: common and glossy. The Wisconsin Department of Natural Resources (DNR) reminds the public that while these aggressive plants and serial invaders are common in Wisconsin forests, there is also a benign and native buckthorn that gets much less attention.

Many people are surprised to learn about this small shrub that has eluded notoriety, unlike its close relatives. Native buckthorn, also known as alder-leaved buckthorn (Rhamnus alnifolia), is a demure shrub that doesn’t grow much taller than 3 feet and prefers wet areas with calcium in the soil.

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Beware Of Bittersweet In Fall Decor

Photo of round leaf bittersweet berries

The berries of round leaf bittersweet (Celastrus orbiculatus) grow in clusters at each leaf axil. The highly invasive nature of this plant makes it unsuitable for use in fall decorations. / Photo Credit: Chris Evans, University of Illinois,

By Erika Segerson-Mueller, Invasive Plant Program Specialist, Oshkosh Service Center; or 715-492-0391

When temperatures begin to cool and back-to-school sales emerge, our thoughts turn to pumpkin spice, sweater weather and all things fall décor.

But as you gear up for spooky season this year, the Wisconsin Department of Natural Resources (DNR) reminds you to beware of using invasive plants in your decorations.

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Don’t Spread Invasive Plants This Hunting Season

Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center or 715-492-0391

Photo of a hunter walking through a field.

Whether you are headed out to a tree stand in your favorite local forest or a duck blind on the shore of your nearby pond, you can take a few easy precautions to help minimize the spread of invasive plants in your favorite hunting spots. / Photo Credit:

Heading out to your tree stand or hunting blind this fall? Avoid adding invasive species to your hunting party by taking a few simple steps to help protect your woods.

Non-native invasive plants often outcompete native plants in forest environments, degrading diversity and destroying wildlife habitat. Invasive plants can replace local forest species and may interfere with or decrease tree regeneration. They may take over woodlands, prairies and wetlands, and many provide ideal habitats for pests that harm wildlife and people alike.

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Yard Waste: Not For The Woods

Erika Segerson-Mueller, DNR Invasive Plant Program Specialist, Oshkosh Service Center or 715-492-0391

Photo of garden waste dumped along an ATV trail in a Wisconsin state forest.

This garden waste was dumped along an ATV trail in a state forest and can be a pathway for invasive plants and diseases that affect our public lands. / Photo Credit: Wisconsin DNR

When a pile of more than 500 pounds of uncooked pasta was found in the woods in New Jersey in early May, no one was quite sure why or how the piles had appeared — but it was clear that they didn’t belong there.

Whether spaghetti noodles, broken electronics or old furniture, some things shouldn’t be in our woods, waters or roadsides, no matter the reason.

Though it may seem obvious that you should avoid dumping these types of waste in your local woods, some items aren’t as straightforward.

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Is it Invasive Giant Hogweed?

Erika Segerson-Mueller, DNR Forest Health invasive plants program specialist, Oshkosh or 715-492-0391

Photo of umbel of a giant hogweed plant.

Umbel of a giant hogweed plant. This invasive plant can grow stems 2-4 inches in diameter and can grow as tall as 15 feet. Photo: USDA APHIS PPQ, Oxford, North Carolina;

This time of year, calls start rolling in about potential sightings of the invasive plant giant hogweed (Heracleum mantegazzianum). Although occurrences of the plant remain rare in Wisconsin, from late May through early July giant hogweed is often confused with a native plant, cow parsnip (Heracleum maximum).

Both are large plants with similar habitat preferences. They prefer shady areas and are often found along stream banks, roadsides and ditches. Giant hogweed is a prohibited species under Wisconsin’s Invasive Species Rule NR40. Its fast growth rate crowds out native vegetation and erodes soil, and skin contact can potentially cause irritation.

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