Dealing with Invasives in Winter

This is a pretty typical scene when English ivy gets established
in a tree.  This ivy is robbing light from the tree and also weighing
 it down, leading to limb breakage.  Cutting a section of each vine
around the base of this tree will kill all the vine above the cut in a month or so.

Wintercreeper grows up trees with the aid of sticky rootlets. 
Its evergreen foliage shades the host trees as well as
the surrounding area.  In areas with plentiful deer the bottom 4'
 are often stripped of foliage.  The same can be seen with English ivy.     

Winter is a very good time to have an impact on Mid-Atlantic invasive plants.  Many of these still have leaves and are susceptible to herbicide treatments.  It’s also easier to see where plants are (though identification can be trickier). Most native species are dormant during winter so there is less risk of damage from herbicides or from tromping through the landscape.  In can be more comfortable to work in cooler weather.  As long as it is above 45°F, many herbicides are still effective (see below). 

When I look out at unmanaged areas infested with invasive plants I see many opportunities to have a large impact on reducing the spread of many of these species without a lot of effort.  For some species just keeping them from climbing up the tree will have a huge impact on controlling their spread.  OF course complete removal for most of these species will take several years of consistent effort, but just keeping them from climbing trees can limit their spread and be much healthier for your established trees and large shrubs. 

Among the species that need to climb in order to bloom and produce seeds are English ivy, Japanese honeysuckle, winter creeper, and oriental bittersweet.  These vining species produce flowers when they are growing upwards or over the tops of other plants.  You can significantly reduce their seed production by keeping them from growing upwards.  Most simply this can be done by cutting the vines growing into trees and larger shrubs close to ground level.  Applying the appropriate herbicide to the stump will go one step further in eliminating that plant from the landscape.  If you aren’t using herbicide, clear the invasive from a zone around the base of a tree to help slow re-establishment of the invasive vine. 

The bittersweet, wisteria and honeysuckle grow upwards by twining around their hosts.  These vines grow tightly around the trunks and branches of their host plants in effect strangling them.  While English ivy and wintercreeper don’t twine as much (they climb with the help of sticky rootlets growing from the stem) its dense evergreen foliage gets very heavy, especially in winter, and can bring down branches or even whole trees.

Oriental bittersweet can grow vertically by twining around itself. 
Once it finds a suitable host it will continue upward
growing around the host.  I cut this one high last spring so
that I could come back later and treat a fresh cut with herbicide.

This Japanese honeysuckle was cut last season.  You can see
 the damage caused by this tightly twining vine.

The table below summarizes how to treat several of the invasive species in fall and winter.  All this information was taken from the references cited.  For details check out the links to the references for each species.  Before using herbicide read and follow the label directions.  Don’t forget to wear proper protective equipment.  Another important safety practice in dealing with vines is to NOT pull them out of the trees after you cut them.  You risk damaging the tree and yourself.  They will dry up and fall out on their own.

Invasive	Common name	Winter treatments	timing	Reference
Celastrus orbiculatus	Oriental Bittersweet	Cut stump treatment with 20% glyphosate or  trichlopyr. Digging/pulling partially effective, but plants can regrow from root fragments.	Fall-Winter when temps above 40°F.   Digging can be done anytime.	Bugwood CO
Lonicera japonica	Japanese honeysuckle	Foliar treatments with glyphosate (0.75-1.5%) effective.  Later in season higher concentrations are more effective.  Use for easily accessible foliage (ground level).	After first frost but before hard frost are very effective.  Mid-winter treatments were less effective.	Bugwood LJ
		Cut stump (25% glyphosate) for climbing honeysuckle vines	Cut stump most effective June-Winter	PRISM
Euonymus fortunei	Wintercreeper euonymus	Cut back climbing vines to prevent flowering and fruiting.  Small infestations can be dug out, but plants can regenerate from stem fragments.	Anytime, the sooner the better.   Flowers form in summer with ripe fruits in fall on climbing vines.  Dig plants when soil is soft and easily worked.	Forest Service
		Cut stem treatment with 25% glyphosate for climbing vines. Foliar spray with glyphosate or triclopyr (2%) for large infestations on ground	When temperatures are above 40°F.  Treat immediately after cutting. Mid to late fall when other species are dormant.  Best at or above 65°F.	TN Exotic Plant Management Manual
Hedera helix	English ivy	Cut vines growing up trees close to ground and again 1-2’ up.  If possible, treat cut stump with 25% active ingredient glyphosate or triclopyr amine.	Cut stump method is effective year round.  Herbicide treatment best when temperatures are above 55°F.	Invasive.org
		Foliar treatment with these chemicals (2-5%) when temperatures are above 55°F are partially effective.	Foliar treatments most effective from mid-summer through fall.  Partially effective in winter.  Apply during mild periods (above 55°F) while other plants are dormant.
		Smaller non-climbing infestations can be manually removed.  Plants can resprout from any remaining roots or vine.	Pulling can be done anytime.  There are fewer competitive plants in winter.
Wisteria sp.	Wisteria	Cut vines about 2” from the ground.  Treat with 25% glyphosate or trichlopyr.  Plants will resprout if not treated with herbicide. Small infestations can be dug out, but resprouting is possible from pieces left behind.	Cut stump treatment can be done anytime that the ground is not frozen.	Bugwood

NOTE: In most jurisdictions a home owner can apply OTC herbicides to their own properties, but they are restricted from doing so on public lands or on another person’s property.  In most cases a certified pesticide applicator is need to apply herbicides to any property but your own.

Before attacking the invasive species it is important to be able to know which plants are desirable and which are not.  Some species are easy to identify in winter (e.g., English ivy and wintercreeper).  Others like oriental bittersweet, can be difficult to distinguish from their domestic relatives.  Check out this guide from the Delaware Department of Agriculture for help in identifying invasive plant species.  Of course any vine that is threatening the life of a desirable tree or shrub is a candidate for removal.  

This adolescent hickory tree sustained damage from
Japanese honeysuckle a few years back.  The truck is swollen
due to sap being restricted from flowing up the tree.  I'm not sure
if this tree will continue to survive into maturity.

In looking over the nearby woodlands I noticed that most of the native vining species do not spiral tightly around their host.   Deciduous native vines like Virginia creeper and native grapes do not twine so they do not strangle trees, and, since they lose their leaves in the fall they do not add a lot of weight through the winter.  Native vines growing high into trees can reduce the amount of light penetrating the tree canopy.  One of the bigger problems on my property with vines growing up in the canopy is that they join trees together so that when one falls it can damage other trees that are connected through the vines.  An important benefit of these native species is that their berries are an import food source for many birds, poison ivy included.

Catbrier (Smilax sp.), the green stems here, is a native species that twines
loosely on itself as well as on other nearby plants.  While it can
 be a nuisance due to its stiff thorns it plays well with other established plants.

Another group of invasive species that can be attacked in winter are woody shrubs and herbaceous species that are still green and active in the winter months.  These include multiflora rose (Rosa multiflora), wineberry (Rubus phoenicolasius) and garlic mustard (Alliaria petiolata).  Last year I wrote a more detailed post  on how to deal with these species in the winter. 

As an update to that post, I did test whether burning the crowns of wineberry with a garden torch was sufficient to kill it.  In most cases the answer was no.  Most of the crown resprouted later in the spring. Another action took was to  cut back the long arching branches in late summer and fall.  This shoud reduce its spread since it can form roots wherever a branch tip contacts the ground.  The effectiveness of this effort will be difficult for me to measure but I hope to get a sense if there are fewer of these out there.

For a general overview of Mid-Atlantic invasive species see Plant Invaders of  Mid-Atlantic Natural Areas  For detailed instructions on how to treat you should look to nearby state resources or University cooperative extension services.

What else can you do?

Aside from managing your own property there is not a lot an individual can due by themselves or without permission.   There are a number of ways to volunteer to do plant conservation or get involved with removal of invasive species.  I first got started working with native plants by becoming a plant conservation volunteer with what was then the New England Native Plant Society (now the Native Plant Trust).  A number of our projects involved clearing out invasive species from public and some private lands.  We were trained on how to identify our target and how to remove it.

To work on public lands you need training and or supervision.  Contact the public lands supervisor for the areas where you want to help.  Some other places where you can look for opportunities are plant conservation groups and state or regional native plant societies.  In Maryland there are several counties with ‘Weed Warrior’ groups (for example see  Weed Warriors  for Montgomery County).  In Northern Virginia there are the Tree Rescuers.  Also in Virginia there is  Blue Ridge Prism, a group dedicated to removing invasives from the forests of the Blue Ridge Mountains.  The USDA website has some general information including a few specific links to projects around the country.  The Nature Conservancy has a volunteer site that can be searched by location and date.

Managing Invasives 2022

This is pretty typical of an 'invaded' tree with
Japanese honeysuckle and oriental bittersweet
 twining among its branches.

We’ve been on our central Maryland property for about 9 years now.  From day one we have been battling a slew of invasive species that were covering the ground and trees through the woodland landscape.  While we still have a ways to go I feel that we have made some good progress.  As I am getting ready to start another season managing the landscape I thought I would organize my plan around actions and timing, rather than looking at one species at a time. 

First 

My first activity for the year will be to treat any visible garlic mustard, Alliaria petiolata, with a 2% glyphosate spray.  I'll do this sometime in the middle of March, when the temperatures  will be above 40°F with no rain for a couple of days. I started doing this 2 years ago and it seems to have helped me get the upper hand.  Prior to that I had  been only been pulling up plants in mid-spring as they grew tall prior to blooming. This link to my post on garlic mustard control options describes winter spraying in more detail and shows some of the desirable native species that may be visible at that time.  It also summarizes control options throughout the year.  The timing is critical as it is before the spring ephemerals, like spring beauties and Dutchman's breeches begin to sprout.  This lowers the chances of harming native species.   

Here you can see what a small garlic mustard, Alliaria petiolata,
looks like in winter.  Indian mock strawberry, Potentilla indica,
is also green through the winter.  Unfortunately, that weed is not
 as sensitive to glyphosate as the garlic mustard. 
See this link for methods to manage it.

Second

Cutting woody invasives and vines and stump treating with 20% glyphosate can be done anytime of the year that the temperatures will be over 40°F for a few days in a row.  Winter is a good time to do this as it is easier to get to the base of many or these plants and there is less chance of getting the herbicide on desirable plants.  Particularly troublesome on my property are multiflora rose, Rosa multiflora, oriental bittersweet, Celastrus orbiculatus, Japanese honeysuckle, Lonicera japonica, and to a lesser extent Autumn olive, Eleagnus umbellata.  An excellent reference for managing invasives in the Mid-Atlantic region is Plant Invaders of Mid-Atlantic Natural Areas. 

In doing dormant season treatments it is critical to be able to distinguish friend and foe.  Below are some images of multiflora rose and other native species that it might be confused with.  

Here is multiflora rose in the winter.  Some distinguishing features are
its round olive green branches and its curved thorns.  The most
distinctive feature are the fringed stipules at the base of the petiole,
shown in the inset above.  It is the only species with this type of stipule.

 

Most native roses do not have green branches in
winter. Thorn shapes vary.  Here, swamp rose has
straight needle-like thorns.

Cat briar has bright green branches in winter
and it has straight almost pyramidal thorns.

Wild blackberry has smooth red stems in winter
armed with stiff red spines. Older branches
are square with indentions on each face.   

Black raspberry has red canes with somewhat smaller thorns. 
It is distinguished by the white bloom on the older branches 

You can read more about  dormant season treatment of multiflora rose at the link.  This technique is also effective on English ivy, Hedera helix.  Even if you don't use herbicides to treat the cut stumps, cutting vines climbing trees and over shrubs is helpful in controlling the spread of these invasives.  This is because many of these species are only able to bloom on vines that are elevated and/or exposed to plentiful sunlight.

Oriental bittersweet can twine against itself to get
stiffer and climb higher.  I cut these a while back
but left them long so I could easily find them. 
I'll cut them shorter and treat with glyphosate later.

This is typical of the damage that Japanese
 honeysuckle can do to a tree.  This vine can be
 recognized in winter in that it still has leaves and
 the older branches have shaggy bark.  

Third

Around the end of March I will use a brush cutter and mower to cut down last years growth of vines and undesired woody plants in the meadow and woodland edges.  The biggest problem in my meadow is wineberry, Rubus phoenicolasius. In addition to the wineberry there are the aforementioned multiflora rose, autumn olive, and oriental bittersweet.  

Spring mowing and pulling has been pretty effective at reducing wineberry in shady areas. This is a short-lived species and not deeply rooted so it is usually easy to pull up.  Cutting to the ground in spring seems to keep it from blooming, but it is still able to reproduce by it ability to put down roots wherever a branch touches the soil.   It is recommended that mowing/cutting should be done several times each season to be truly effective.  This is particularly true in sunnier areas where the cut plants can rebound quickly.  Oriental bittersweet can also resprout easily after being cut.

Wineberry is easily recognized by its dense
coating of stiff hairs mixed with red spines. 
While formidable in appearance these are
easily crushed with a gloved hand.

I will return about a month later and do a foliar spray on the wineberry sprouts. While burning is not considered an effective option of wineberry control I will test out targeted ‘cooking’ of individual crowns with my garden torch to see if that kills them in place.  (Standard burns do not selectively kill the wineberry, rather it clears out the competition and allows it to grow unhindered.

Fourth

At about the time that the forsythia is beginning to bloom is the time for me to get started on Japanese stiltgrass, Microstegium vinineum, control.  Stiltgrass has definitely been reduced in the lawn by use of a pre-emergent herbicide originally used for crabgrass control.  It should be applied when forsythia are beginning to bloom.  If you want to be more precise you can use a growing degree day tracker geared toward turf management. like GDD Tracker 4.0. The product I use contains only dithiopyr (Dimension™) and no added fertilizer.  Most of my lawn is fescue based and not that hungry for added nutrition.  This link lists some other preemergent products that have shown effectiveness against stiltgrass.  I wrote about my year long plan for controlling stiltgrass in this post.  In the woods pulling and weed whacking, particularly in late summer has reduced, but not eliminated the amount of stiltgrass.  As a result of thinning out the stiltgrass, I am seeing more native species filling in such as white avens and Virginia jumpseed.  I am also seeing an increase in perennial grasses (perhaps a Glyceria species) in areas where stiltgrass had dominated. 

In the sunny meadow stiltgrass has been harder to eliminate.  The preemergent has not been as effective on the rougher soil and I am hesitant to use it every year as it may negatively affect the growth of desirable plants from seed.  Summertime pulling and the addition of tough native grasses and forbs is helping to displace the stiltgrass.  Weed whacking close to the soil level in late summer as the stiltgrass is beginning to bloom is effective.  However this will also damage other desirable species.  The best method or methods to use depend on the situation in a given location. 

Rest of Year

Mid-spring is the time when I will be watch for the rapid growth of garlic mustard as it prepares to flower.  Pulling it out and leaving it in the sun to dry is my method of choice at that time.  

Late-July and August are the time for pulling out stiltgrass as it prepares to bloom.

So there appears to be an awful lot to do, but it is encouraging that I have seen some progress.  I realize that I am talking about using a lot of herbicide, but these treatments are targeted on the actual plants and done at a time that has little negative impact on native species.  In this battle I feel it is necessary to properly use all the tools that are available.  Another aspect of invasive species control, is limited resources, especially time.  It is better to do one area really well, then move on to the next, rather than doing a little bit everywhere.

I wish you all good luck as another growing season is upon us!