Invasives-Schminvasives, Part 2
Asiatic Bittersweet
How do I hate thee?
Let me count the ways! Asiatic bittersweet (Celastrus orbiculatus) is one of my (least) favorite invasives for several reasons. It was my own personal introduction to invasives, discovered as it was swallowing several of my favorite trees and shrubs whole about 10 years ago, as it will do if left unchecked. I quickly began referring to it as “evil bittersweet” anytime I’d find it climbing another shrub or tree, and it only took another season before every new discovery of it resulted in its new, and now permanent, name on my property, “f^@#*ng bittersweet.”
Asiatic bittersweet is a vine that was introduced to the US sometime in the mid-1800s. (WHY, you may ask? “For ornamental purposes,” as is so often the case with the introduction of a seemingly innocuous plant that has characteristics we find attractive. Then, before you know it, it’s eating your landscape). Now, it should be no surprise that it has spread south and west, and, when left to its own devious devices, can grow to 60 feet tall over just a few years, and develop twisting, strangling, woody, almost trunk-like stems and roots as it matures.
It will climb up and through your trees and shrubs, and the longer it’s left untouched, the larger the root system and stems grow, and the more tightly they wrap themselves around the trunks and branches of their victims. Eventually they either girdle the target (essentially strangling it), or the leaves form a dense canopy that overtakes the canopy of their hosts and starve them of sunlight, preventing photosynthesis, further weakening and eventually killing even massive, mature hardwood trees. Drive down many highways (in the northeast, anyway), and if you’ll probably see it, literally covering entire swaths of roadside forest. It probably goes without saying, but I’ll say it anyway for emphasis: this is NOT good for the trees.
Mature vine of Asiatic bittersweet girdling a near-dead hardwood. Photo courtesy of the author
Asiatic bittersweet overtaking a forest edge. Photo courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
How do they spread?
This insidious plant spreads in a couple of ways: first, if allowed to mature, it develops an extensive root system, and sprouts from that system. This means that unless you can kill off the entire thing, roots and all, it will continue to sprout new growth from the hidden roots. The older they get, the thicker, harder, and more difficult the roots are to pull in their entirety, and anything left behind? You guessed it: it’s just gonna keep sprouting.
Second, female plants produce berries, which, in the absence of plentiful enough native late-season fruits, are eaten by birds, and, once pooped out, sow themselves into brand new plants wherever they land. And those oh-so-pretty yellow and red fruits that everyone loves in their wreaths? The seeds in those berries remain viable even when the berries dry out, so they sprout wherever they fall. F^@#*ng bittersweet.
Identification
First, there is a bittersweet that’s native to North America. American bittersweet (Celastrus scandens) has slight variations in leaf shape (more oblong for the native with a longer, pointier leaf tip, v more rounded leaf for the invasive), stems (blunt thorns on the native; smooth stems on the invasive), flowers (both are tiny, but the female plants of the native have flower clusters only at the ends of the vines, while the female of the invasive plant has flower clusters all along the stem at the bases of the leaves), and fruit (before the fruit splits open in the fall, the berries of the native are yellow, while they are orange for the Asiatic invasive variety). Another easy way to identify the invasive variety of bittersweet: when you pull it, the roots are distinctly orange-tinted.
Asiatic bittersweet seedling (with a tendril of English ivy above, which, now that I see it, I’m going to have to go out and pull! Darker green Virginia creeper beneath). Photo courtesy of the author
That same seedling, two minutes later, showing its classic orange root. Photo courtesy of the author
A more mature tendril of Asiatic bittersweet. Photo courtesy of the author
American bittersweet leaf and berry. Note the more oblong leaf and berries only at the ends of branches. Photo courtesy of John Hagstrom
If you live in the northeast, you likely won’t have the opportunity to distinguish between the native and the invasive, though. It has become so rare that you’re very unlikely to encounter it. It has, quite unfortunately, been both out-competed by and hybridized with Asiatic bittersweet, which grows much faster and larger than the native. What you may encounter instead are a couple of other native vines, both of which are easy to distinguish from Asiatic bittersweet: the dreaded poison ivy (Toxicodendron radicans) and Virginia creeper (Parthenocissus quinquefolia).
I totally understand the fear and loathing that accompany poison ivy, but, as I mentioned in my initial invasives post it is actually beneficial to native animals who consume both the leaves and berries. Virginia creeper also gets a bad rap, but it, too, is super-beneficial without the horrible rash (though some people are allergic to it, it’s nothing like poison ivy). Please, please, if you have either, unless they’re in a really bad spot or are overtaking a tree, shrub, or other plant, consider leaving them! Virginia creeper especially can be trained over fences, trellises, or walls and can look quite lovely anywhere you’d consider planting (horrible, invasive, damaging) English Ivy.
A (hopefully helpful) note about identification
A very worthwhile “investment” is good plant ID app to install on your smartphone. I use Picture This, which I’ve found has become fairly accurate (but if I have any doubt, or if it’s a first encounter with a given plant, I’ll double check the results against images on Google). Picture This is $29.99 for an annual subscription.
There are many others out there as well, and some that I believe are free (Seek, for example, though ID with this app can be tedious and often gets only to genus or class and not all the way to species. When it does get all the way there, I find it to be very accurate). Nevertheless, it’s always a good idea to double- or even triple-check any result against other sources, especially if you’re just getting started or you’re observing something for the first time. I also recommend joining a native plant group for your geography on Facebook, as well as a group specializing in invasive plants and controls. I have learned TONS by being part of a few of these groups over the past few years!! Feel free to reach out to me if you have any questions!
Controlling the monster
I’ve been able to control this beast on my property, but fair warning: if you don’t stay vigilant, it WILL ALWAYS come back. As long as it exists anywhere, its return is nearly inevitable, mainly due to the berries and the birds. Fortunately, once you get it under control, it’s not too hard to keep it under control.
If it’s climbing your trees or shrubs, double-cut it: first at/near the base of the tree or shrub, and again at chest height, so you’ve taken out several-foot-long sections of it. (Some advocate for leaving a foot or two of the main vine above ground to make it easier to find next year). Be sure to check all around the base of the host plant and try to cut every stem you can find. DO NOT attempt to pull the vines down from the upper branches of the host plant if it’s grown fairly high up into the canopy; you’ll risk injuring the host and pulling down leaves it will need to photosynthesize and regain its health/strength. The cut upper sections of the vine will dry out and die once cut.
If the main vine doesn’t seem too large/mature (stem less than 1/2” in diameter), you may be able to pull it successfully. Wait, if possible, until the ground is soft – after a rain, for example. Grab the base of the vine it as close to the ground as you can get, wiggle to loosen as much as you can, and pull back firmly but gently in the opposite direction of growth, working to be sure to get the whole thing. Then, either lay it in a hot, dry, sunny spot to dry it out and kill it (should be pretty-well dead within a few days), or bag it in black plastic and leave it, securely closed, to die before disposing of it. Never compost it or just throw it aside as it will just re-root itself and keep going. F^@#*ng bittersweet.
If the main vine you’ve cut is larger and more mature and it’s before late August, just patrol it and watch for new growth, which you can carefully paint or spray with glyphosate (Round-up). If you don’t want to use chemical warfare, you can continue to cut or pull any new growth, or you can smother the entire area with a thick (at least 3” 0 I find 4” to be optimal) layer of mulch, maybe undergirded by landscape fabric if you really want to go whole-hog. I’m not aware of any non-chemical solutions beyond this other than constant vigilance and cutting/pulling of all new growth as soon as you see it to starve the root system by preventing photosynthesis. Note that even if you’re using chemicals, you should also continue to look for any new shoots, which could pop up anywhere along the root system if it hasn’t been successfully killed. That means looking within at least a 25’ radius of your main cut (or more) since those roots could be coming from any direction.
For practical reasons, I’m going to return to effective and (relatively) safe chemical warfare for a moment, which may be your only hope if you are unlucky enough to have a bad infestation. First, understand bittersweet’s growing cycle, and when it’s vulnerable to eradication efforts: in spring and early-mid summer, it’s emerging and actively growing, reaching for the sun for photosynthesis and strength. This is a time for pulling and cutting of any and all new and existing green growth to minimize the plant’s ability to continue growing and bringing energy to the roots through photosynthesis.
I have found that this is NOT the best time for chemical treatments for the following reason: this is the time that sap is flowing up/out to the plant’s extremities. Since chemical eradication works by the plant’s drawing of the chemical into the root system and the “flow” simply isn’t going primarily in that direction at this time, this method is not nearly as effective at this point in the growth cycle.
Once you’re into summer, the plant’s energy is going into production and maturation of fruit, and then, heading into fall, energy is being drawn down into the roots for winter storage. THIS is the best and most effective time, I’ve found, for chemical treatment.
For very mature vines with large, thick stems and roots that are NOT intertwined in the root system of a host plant you want to keep, you may need to use a saw (or chainsaw) to cut through them. Cut on a 45-degree angle to maximize surface area, and, using a foam paintbrush, carefully paint the entire cut surface, immediately after cutting, with brush killer (usually triclopyr). You can also use glyphosate, but I’ve found triclopyr to be more effective. Please note, however, that triclopyr CAN TRANSFER to other nearby root systems, which is why you should never use it on a vine whose roots are intertwined with those of a desirable host plant. Glyphosate, on the other hand, doesn’t transfer. You must paint the cut immediately after cutting because the cut will begin to heal within minutes and make the application much less effective. Mark the spot so you can find it in spring and monitor for any growth that may fight its way back.
If you have a really tough infestation entangled within a root system (as I did in a very mature native juniper whose roots, and the HUGE bittersweet roots that were entangled with it, were growing between large boulders on a hill), you can try the method that worked miraculously for me. I waited until fall (late September, if I remember correctly), and picked a dry day. I took an 8 oz plastic water bottle and carefully filled it halfway with glyphosate, capped it, and put it within easy reach, along with a roll of duct tape and my pruners. I found a spot in the juniper where I could grab the ends of several stems of bittersweet and twisted them together. I duct-taped the twisted bunch together as tightly as I could, making the bunch small enough to fit through the top of the water bottle, then cut the ends on an angle to maximize the surface area. I retrieved the bottle and carefully uncapped it, making sure not to spill any (the reason I only filled it halfway). I think I still may have had to cut the neck of the bottle open further so the bunch would fit, which I did with my pruners. I shoved the bunch far enough into the bottle that the cut ends were submerged in the glyphosate by a few inches, then duct-taped around the top of the bottle and the protruding stem bunch to secure the bunch into the bottle to be sure it stayed there. I left it there all winter and through the following season. I’ve never seen bittersweet in that juniper since!
There are many who also advocate glyphosate or triclopyr treatments during active growth periods, but I personally don’t believe in this at a large scale unless it’s an emergency situation as I really don’t think it’s as effective as hitting it hard late in the season, and you end up using a lot more chemical over time than I believe is truly necessary. As I noted earlier, however, if you’re working on a vine you’ve already begun to weaken by cutting and you’re now monitoring for new growth, treating the new growth can be effective, but during growth season, I find that it’s just as tedious as pulling/cutting new growth, and only slightly more effective.
If you do use chemical controls, PLEASE be VERY CAUTIOUS and always wear protective gloves (I have a pair of heavy-duty rubber gloves I wear faithfully whenever I’m handling glyphosate or triclopyr). The stuff is very unhealthy if it comes into contact with your skin, and it can easily harm other plants with even a splash, so don’t be cavalier with it.
Once you have Asiatic bittersweet mostly under control, make patrolling for seedlings (anywhere – especially under shrubs and trees with a lot of bird activity) and regrowth on or around old stumps or roots part of your regular walks around your yard/property. If you pull/cut/starve the young plants/new growth, they’re relatively easy to manage going forward.
Controls, in summary
Understand growth cycle:
Spring & early summer - sap flowing upward & seeking light/energy for growth;
Summer – putting energy into fruit production;
Fall – drawing energy down into roots for winter storage
2. Attack according to growth cycle:
Spring & Summer – pull smaller plants/shoots; cut; watch for regrowth & cut/pull the regrowth – deprive it of as much opportunity for photosynthesis as possible;
Fall – take advantage of its natural tendency to draw energy into the roots and apply appropriate chemical treatment carefully and sparingly.
For more detail on background, identification, and control methods, check out any of the bulletins published by your local ag extension, or any of several universities who’ve spent decades researching treatments & methods, for example, this one from Penn State.
Until next time, get out and explore/enjoy your yard!!
