Dealing with Invasives in the Winter

Fall and winter are good times to use herbicides to control invasives.  At this time it is easier to spot many invasive species because they often hold onto their leaves longer than native species and there is less likelihood of harming native species with any mis-directed herbicide.  However not all invasive species can be treated effectively during this period.  At their January meeting, Blue Ridge Prism, an organization based in Virginia to address the threat of invasive species and to restore native habitats, the topic was about which plants could be treated over the winter months. A recording of that meeting can be found at this link:  January Meeting.  For each species mentioned here there are links to Blue Ridge Prism's  Fact sheets .  These provide lots of information each species including how to identify them and others species that may look similar.

One of the most obvious targets for winter actions are invasive vines growing up trees.  These include  English ivy, Hedera helix, and winter creeper, Euonymus fortunii.  At a minimum, these vines should be cut at the base of the tree and again a few inches to a foot or so up to create a gap.  If possible the lower stump of the vine should be treated with a 50% dilution of a recommended herbicide (e.g., 20% solution of glyphosate) to kill the roots.  This is referred to as the cut stump treatment.  The remaining vines in the tree should be left in place to slowly die.  Attempting removal can damage the tree and/or injure folks on the ground with falling debris.  Be observant when cutting the vines, wintercreeper vines especially are good at hiding in the furrows of the bark of trees. 

This tree has surrendered tp English Ivy.  The added weight
 can cause limbs to break, particularly with
accumulated snow and ice in winter.

These trees have winter creeper euonymus climbing up.  Winter creeper
sends out longer branches than English ivy.  These branches will bear
flowers resulting in the spread of this invasive species. 
Note that both of these vines have been 'deer pruned',
 but doesn't keep them from climbing.

For plants growing along the ground, these evergreen vines can also be treated with foliar sprays in winter, though not with 100% success.  Digging when the ground is soft and moist is quite effective at any time of year.

While not expressly discussed, Japanese honeysuckle, Lonicera japonica, vines cane also be treated in late fall and winter by either cut stump or foliar spray, if leaves are present.

Winter foliar spraying of  Vinca (V. minor and major) was reported to be effective, though personally I have not seen satisfying results.  For small infestations hand pulling is very effective.  I find that using a rake to lift most of the stems followed by using a trowel to get out the rooted plants is pretty effective.  Many folks recommend cutting, mowing or weed whacking first, then, later, hitting the regrowth with a foliar herbicide.  In doing this one must be very careful about killing non-target plants.  (These herbicide treatments are likely to be during a time while desirable plants are actively growing as well.)

There is not much else growing around this patch of Vinca minor
(Periwinkle) in January so careful foliar spraying shouldn't damage other plants.

I do have several areas where vinca has escaped the beds and is moving into forested areas.  Later in February I will try an experiment with foliar spraying alone compared with string trimming + raking followed by a spray with glyphosate.  There are some natives in this area, such as white avens, so I don't want to wait too long before I get started on this.

Fall and winter are good times to treat garlic mustard, Allairia petiolata.  The leafy rosettes of overwintering plants are easy to spot treat with the appropriate herbicide when other plants are still dormant.  Treatments can be done when temperatures are above 40°F.  I've done treatments in November and February-March. In my opinion the treatments later in winter were more effective because the leaf litter had broken down more making the garlic mustard leaves easier to target.  See this link to an earlier blog post about my efforts to eliminate garlic mustard.

Here's some garlic mustard in November,  In a mild winter
 these leaves will remain active all season.  Around March
 they will begin a growth spurt and put up a flowering stalk.

Gill-over-the-ground or creeping Charlie, Glechoma hederacea, can be treated with foliar sprays in early winter before a hard frost, but these would be more effective in early fall while plants are moving nutrients to their roots.  By January  most of the leaves have fallen off so there is no good target for a foliar spray.  Multiple treatments will likely be necessary.  The advantage of winter spraying, again, is that there are few non-target species actively growing at that time.

For Autumn olive, Elaeagnus umbellata, Nandina, Nandina domestica, and Bradford pear, Pyrus calleryana (fall to early winter), cut stump, hack and spray or basal bark treatments are effective. Autumn olive and Nandina can be treated effectively through the fall and winter. Treatment is not so effective in early spring when sap is flowing upwards.  Bradford pear should be treated earlier, while sap is still flowing downwards to the roots.  Smaller plants can be cut close to the ground and immediately treated with a concentrated herbicide on the stump.  Larger specimens can be treated using basal bark treatments (herbicide in an oil carrier) or hack and squirt.

These autumn olive bushes are in full bloom with their sweetly scented
 flowers seen here in early May.  I eliminated both of these with the
cut stump method using glyphosate.

While some invasive species can be treated throughout the winter months, usually when temperatures are above 40°F, some require treatment in a more specific time period.  Mid-fall to early winter is a time in which sap is flowing from the upper parts down to the roots.  Herbicide treatments at this time will carry the active ingredients to where they will have the greatest effect.  As mentioned above Bradford pear and gill-over-the-ground should be treated earlier.  Tree-of-heaven and Asiatic bittersweet are also in this group.  

Tree-of-heaven, Ailanthus altissima, is best treated in early fall when the sap is following down to the roots using basal bark or hack and squirt methods.  Cutting the this tree down is not an effective means of control.  The response to being cut down is for it to put out many root sprouts, so even treating the stump with herbicide is not going to be effective. 

Italian arum, Arum italicum, does not have an effective approved herbicide so digging is currently the only effective means of removal.

Lesser Celandine, Ficaria verna, is a major problem in moist areas, particularly along streams.  These can look like violets when not in bloom.  Digging small infestations can be done all year but care must be taken to remove all the roots, tubers, and bulbils, as well as seeds, if present, to avoid recurrence or spreading of this species.  There is a very narrow window of opportunity (about 2 weeks) for effective foliar treatment with glyphosate.  This is in the March-April time frame shortly after the plants have started to bloom, but before full bloom is achieved.  In wetland areas so you need to use a herbicide approved for those places (e.g., Rodeo®). 

This photo of lesser celandine was taken in mid-April toward
the end of the herbicide application window. 
When not in bloom the leaves do look similar to many violets

Some General Comments

Make sure you can positively identify the target species.  Especially with shrubs.  You could always tag the plant of interest with florescent tape in the winter and come back to it when it's leafed out or in flower to do a positive ID.

If you don't wish to use herbicide treatment, winter is a good time for pull up plants at times when the ground is thawed and moist and plants can be easily removed.  Just be careful not to disperse any seeds associated with the plant that you are removing.

For most plants a form of glyphosate will work.  Check the links for specific guidelines for each species.  In general, I prefer glyphosate as it is not translocated in the soil to other plants and that which reaches the soil is broken down quickly by soil bacteria.  In all cases follow the herbicide label instructions.

Just to throw in my own two cents, I wanted to add two things.  First while there is nothing you can do with Japanese stiltgrass  in winter, early spring (when forsythisas are blooming) is when you can put down preemergent herbicides to help eliminate this from lawns and areas where you are not encouraging growth from seeds.  Check this post for details.

Second, winter is also a good time to treat Japanese barberry using a cut stump treatment.  It can be spotted by the few remaining red berries along the stems.  There is a native barberry but it's quite uncommon.  It differs from Japanese barberry in that it has spines in groups of three along it stem, rather than the singular spines on Japanese barberry.

Discovering My Invasives

As we are coming into late spring and I have been marveling about all the native plants I have found a crop of invasive plants has manifested themselves.  I know some of these were lurking out there, others were plants that I had misidentified, but have now reveled themselves now that they are in bloom.  Here a run down on what I've got, but wish I hadn't, and I plan to do about it.

Multiflora Rose, Rosa multiflora, is scattered around the property, mostly in the woodland edges.  These roses can be identified by their frilly stipules (leafy appendages at the base of the petioles), but now are very obvious by the clusters of fragrant, small white flowers.  I had hoped that I had some native roses out in the field, but so far it looks like they are all Multifloras.

Left to its own Multiflora Rose will send stems high into a tree.  

For the plants out in the open I am continuing to mow over them.  For the more established plants I will cut and treat the stumps with concentrated Round-Up in August.  I will do an earlier cut on some plants to prevent this crop of seeds from maturing, but I want to leave enough for easy application of the herbicide later in the season.


It turns out that a couple of small trees that I thought were Pin Cherries are actually Autumn Olives, Elaeagnus umbellata.  My mistake was made clear at the beginning of May when these plants were coming into full bloom.  I was drawn to the wonderful sweet scent.  When I saw the flowers I realized that what I had was definitely not a cherry of any kind.

These two Autumn Olives are nicely situated on either side of a path.
I'll cut them down soon and replace with something native,
maybe Winterberry Holly and Tupelo

These fragrant tubular flowers
were very popular with the bees.

I decided to let these finish flowering before cutting them back to a stump and then treating the fresh cuts with Round-Up concentrate.  This seems to be a pretty general method for killing undesired shrubby vegetation.  I did this to a very large Euonymus alatus in mid-March and I have seen very little if any regrowth so far this season.


When we first moved in last fall I noticed a lot of honeysuckle vines growing everywhere.  I had hoped that they were the native Coral Honeysuckle, Lonicera sempervirens.  There were no berries present (Japanese Honeysuckle has black berries, L. sempervirens has red berries) so I couldn't tell by that.  Also a cross section of the stem appeared to solid, not hollow, so I assumed it wasn't Japanese Honeysuckle.  Now that they are coming into bloom with their sweet-smelling white flowers, I see that I have a lot of the invasive honeysuckle.  A check of the stem shows that these are in fact hollow, so looking at the cross-section of the stem may not be a great late season indicator for this species.

Japanese Honeysuckle flowers start off white, then turn yellow after a couple of days.

I'm not sure what approach to take on all the trailing stems on the ground.  Pulling and late season herbicide applications can be effective (as long as the leaves are still photosynthesizing).  In the interim I have been cutting the stems of the vines up in the trees to minimize seed production.

Garlic Mustard, Alliaria petiolata, is well establish in the wooded areas on and around our property.  I am trying to remove all of it from an area before moving on to a new area.  This is a more effective strategy for elimination than just pulling a few plants here and there from a much wider space.  The seed heads are just about to mature so it's time to take a break from pulling.  If you are pulling plants that are shedding seeds, it's kind of like planting more of them.

Year old rosettes of Garlic Mustard remain green here over the winter.  This gives me the option of either pulling or spraying when most of native plants are dormant.  Because of the diversity of native plants in the woods, I will continue pulling up any Garlic Mustard I see each spring and fall.  this will be a multi-year effort.

Same area after clearing.  The ground plane is now opened up.

Note the white center vein on the leaf.

Japanese Stilt Grass is wide spread in this area.  It fills in shady borders with a dense mass that can smoother out other plants.

As an annual it can be controlled if you can keep it from going to seed.  Cutting it back when it begins to flower in late summer can keep it from successfully setting seed.  Cutting it back earlier may stimulate earlier flowering.  For plants in the woods I will go after them with the weed wackier in August. This grass has a weak root system and is easily pulled up, but there is just so much!

This is a very leafy grass and is soft to the touch.  The shiny mid-rib is a feature that sets it apart from other grasses

This is a recently opened-up area where the stilt grass is going to town.
It is joined by some garlic mustard and  bittersweet.
The near-by poison ivy is slowing my progress here.

Note the triangular leaves of Mile-a-minute vine.
There are nasty thorns forming on all  parts of this vine.

Mile-a-Minute Vine is a very fast growing invasive.  Once I noticed it I took some time out from writing this post to pull it out right away.  It is really important to do this before its many thorns begin to harden.  In my enthusiasm I accidentally pulled up a new Redbud tree, because its heart-shaped leaves looked similar to the triangular leaves of Mile-a-minute.

To combat this invasive, a weevil has been introduced and has been found to be very effective, and selective, at consuming this plant.  I examined the plants I pulled but saw no signs of this insect.  

To keep from going crazy I've realized that these invasives did not appear overnight and that any reasonable action is a step in the right direction.