Monday, December 3, 2012

Identification and control of woody invasive species in fall and winter

By Chris Evans, Illinois Wildlife Action Plan, Invasive Species Campaign
Reprinted from Illinois Forestry Association Fall 2012 Newsletter

With the arrival of autumn comes the changing of the colors of leaves and the ripening of fruits. The onset of the fall and winter seasons also brings an opportunity to easily find woody invasive plants. Many of these invaders turn distinctive colors or stay green longer than native species, allowing for easy identification.

Also, with the cooler temperatures, the disappearance of ticks and chiggers, and the senescence of poison ivy, it is a great time to be out in the woods. As the leaves fall on the trees in our forests, you can see a long distance through the woods and find invasive plants that otherwise would be hard to find.

Even in winter, when the leaves are gone from the invaders, you can still use characteristics like bark color and texture, plant growth habit, stem arrangement, and even fruit to correctly identify these plants.

This article, summarizing a November 2012 IFA webinar on “Dealing with Invasive Species in Fall and Winter”, will discuss the characteristics used to identify several common invasive plants in the dormant season as well as give recommendations for control methods.

For more details on this subject, a recording of the full webinar can be found at

It is important to be sure of your identification in the dormant season before conducting control applications. Misidentification could lead to accidentally controlling a desirable native species. Try to make sure at least three different characteristics check out to verify identification.

Bush Honeysuckle

The yellowing leaves of bush
honeysuckle and the bright red
berries make this plant stand out in the fall.
Perhaps the greatest invasive plant threat to forests in Illinois is bush honeysuckle. This invader is actually a complex of several species, all of which look similar and have comparable impacts.

Bush honeysuckle is a tardily deciduous plant, meaning that it holds on to its leaves longer than most shrubs and trees in Illinois. You can commonly see bush honeysuckle with leaves still hanging on into early winter.

Bush honeysuckle bark is
light tan and looks stringy

The normally dark green leaves typically turn a distinctive yellow-green color in fall. This leaf color, along with bright red (orange-colored in some bush honeysuckle species) berries usually occur in pairs or fours make fall identification extremely easy. 

 Leaves are opposite on bush honeysuckle. If all the leaves have fallen off, then the buds or arrangement of small branches will also be opposite.

Bush honeysuckle also has very distinctive bark, light tan in color and somewhat stringy looking
Once a suspected bush honeysuckle plant is found, a great way to verify its identification is to cut open a small stem. Honeysuckle stems have hollow piths.
Bush honeysuckle twigs will have hollow piths, easily seen by cutting open a stem
Autumn Olive

Autumn olive is one of the most common invasive plants in Illinois. Most landowners can easily identify this plant in the growing season by the silvery underside of the leaves. Luckily, autumn olive usually retains at least some of its leaves well into the dormant season. Additionally, the rusty red berries often hang on into winter.

Autumn olive is usually a multistemmed bush with younger stems being light tan to gray in color and smooth with the older stems becoming more gray and rougher.

Autumn olive is usually a
multi-stemmed bush

Twigs of autumn olive are covered in lenticels
and are rough to the touch
(photo by Robert Vidéki,

The twigs of autumn olive are covered in lenticels, small dots, which give the twigs a rough texture.  Often just running a twig through your figures is enough to verify identification. Thorn-like small branches may be present on autumn olive but is also often missing.

Oriental Bittersweet

Oriental bittersweet is a woody vine that can drastically impact forests. Bittersweet has a somewhat patchy distribution across the state, with some areas being overrun and other areas having no bittersweet. Bittersweet looses it leaves somewhat early in the fall, but does turn a distinctive lime-green to yellow color before fading.

Fruit on female Oriental bittersweet vines have an orange-yellow covering
that splits to reveal scarlet berries.  Oriental bittersweet can wrap tightly around a tree
or coil around itself and it recognizable by the light-gray bark with prominent lenticels

The berries can remain on the female plants late into winter. These berries are bright red under an orangish-yellow capsule that peels back.  These berries occur along the stems in the axils as compared to American bittersweet which would only have berries at the end of the branches.

The bark of Oriental bittersweet is very distinctive and, since often the leaves and fruit occur high in the trees, is a good characteristic to learn! Unlike grapevines, which have dark bark, or trumpeter creeper and Japanese honeysuckle, which have papery bark, bittersweet has a light-gray bark with diamond-shaped lenticels, becoming more flaky as the vines age.

Multiflora Rose

Multiflora rose has stiffed, curved thorns that
usually are in pairs and break off easily
Multiflora rose has long been a thorn in the side of Illinois landowners. This invader is better known for its damage to fields and pastures but also can be a problem in woods.

While this plant doesn’t turn a noticeable color, it does usually retain a few green leaves into late fall. The stiff, curved thorns occur along the stem usually in pairs that break off easily.

The stems of multiflora rose are round (compared to the square stems of blackberries) with the smaller stems being green or sometimes reddish with the larger stems having brownish rough bark.


While there are many more invasive species that can be identified in the fall, the species listed above are four of the biggest threats to forests in Illinois.

Controlling these, and other woody invasive plants, in the fall or winter is often best done using either a cut stump or basal bark application of herbicide.

There are some times when you can apply the herbicides to the foliage and some non-chemical methods of control (both of which are discussed in the webinar listed at the beginning of this article).

The advantage of using a cut stump or basal bark treatment is that the method and herbicides recommended works for all of these species, giving a landowner the option of treating more than one species without needed to change equipment or remix herbicides.

For any herbicide application, it is required that the entire label be read and followed including what type of safety equipment is needed to mix or apply.

Cut Stump

Typically, cut stump treatments of woody invasive plants utilize either glyphosate- or triclopyr- based herbicides. Examples of a glyphosate-based herbicide would be RoundUp, though there are many generics available as well. Examples of triclopyr-based herbicides are Garlon (both 3a and 4), Crossroad (mixed with 2,4-d), and Ortho Brush-B-Gone.

Since these herbicides come in many different formulations and strengths, it is crucial that the label be consulted for the specific herbicide used to determine the correct mixing rates and instructions before use.

A ready-to-use premixed formulation of triclopyr, called Pathfinder II, is effective both for cut stump and basal bark and does not need mixing (though shouldn’t be used in temperatures below 30 degrees).

Cut stump treatments are basically just what they sound like. Cut down the plant near the ground (within 6 inches, but not so close that dirt gets on the cut surface) and treat the cut surface with herbicide.

Typical rates would be a 50% solution of glyphosate mixed with water or a 20% solution of triclopyr mixed with water (for amine formulations like Garlin 3a) or oil (for ester formulations like Garlon 4). Oil used can be a commercially available basal oil (like Bark Oil Blue or AX-IT) or a seed or crop oil.

Adding some herbicide dye into the mixture will help you keep track of what has been treated and avoid misses.

Herbicide dye makes tracking treatments easier
(photo by Jim Miller,
It is important to treat the stumps soon after cutting (ideally within 15 minutes) for best results.

For small stems (less than 2-inch diameter) then treat the entire cut surface just to the point that the herbicide is starting to run down the sides. For larger stems, only the out one inch of the cut surface needs to be treated.

A simple hand-pump spray bottle is a great
tool to use when conducting cut stump
If you are using a solution mixed with water, only use this method if temperatures are above freezing. Cold temperature can freeze the mixture and prevent it from working. Oil-based solutions can be utilized anytime throughout the fall and winter up until the plants start breaking buds in late winter /early spring.

A simple hand-pump spray bottle works great for cut stump treatments but the herbicide can also be applied with a sponge or paint brush.

Basal Bark

It is recommended that an ester-based triclopyr herbicide (for example – Garlon 4 or Crossroad) in oil is used for basal bark treatments. Typical rates would be a 20% solution, though be sure to check label information for the herbicide to be used for specific recommendations. Water-based herbicide mixtures are not effective using this method.

As with cut stump, Pathfinder II is a ready-to-use formulation of triclopyr that can be used for this method. Basal bark is similar to cut stump, but removes the necessity of cutting down the plant first.

Instead, the herbicide is applied directly to the all sides of the bark of the plant from ground level to 12-16 inches high. For multi-stemmed shrubs, all of the stems need to be treated.

This method does use somewhat more herbicide than cut stump but is quicker to apply.

Multi-stemmed shrubs need to have all stems
treated for a basal bark application to be effective
(photo courtesy of Dow Agrosciences)
Because of the higher volume of herbicide needed, a backpack sprayer is the ideal equipment for this method. Hand-carried pressure sprayers or ATV or vehicle-mounted spray rigs can also be used if access allows. As with cut stump, mixing in herbicide dye is a good idea to track treatments.

Basal bark can be used throughout the fall and winter. Heavy snow cover seems to reduce effectiveness as do wet – or silt-covered stems.

Don’t be alarmed if the plants treated in the dormant season using basal bark leaf out in the spring. This sometimes happens but usually the leaves will wilt and the plant will then die. Just keep an eye on the treated plants and be prepared to retreat if necessary.

Utilizing these tips for identifying and controlling woody invasive plants will hopefully allow landowners to better address invasive plants in their woods. Don’t expect to get rid of all of the invasives with just one round of treatments. Plan on eradication taking 3-5 years with the most of the work occurring in the first two years.

For information on invasive plants and management can be found in the Invasive Plant section of the IFA website and on

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