Hercules is a hero in Greek and Roman mythology who is familiar to many of us for his great strength. There are many legends and stories about him, but one of the most well-known is the twelve labors that were assigned to him. One of these labors was to slay a serpent called the Hydra of Lerna. This serpent had nine heads and if one was cut off, two would grow back in its place. One head was said to be immortal which made his battle even more difficult.
Sound familiar to anyone trying to deal with invasive shrubs on the prairie? We have all had the experience of cutting and treating brush such as buckthorn or honeysuckle only to have it, like the Hydra, regrow one or even a whole slew of heads- resprouts! These resprouts can make our restoration efforts much harder and time consuming. Often there seem to be resprouts on at least a few plants even with the most careful and meticulous technique, such as in the following photo of one buckthorn stem that was not adequately treated and turned into almost 30 resprouts!
Buckthorn Previously Cut but Growing Back with Resprouts
So, how did Hercules win his battle? Well, he had a little help from his nephew, Iolaus, who used some sort of special torch to cauterize the severed necks before they could regrow a head. And he also had help from the goddess Athena who provided him with a special golden sword to cut off the immortal head which Hercules quickly buried under a heavy rock. And there you have it- no more "resprouts”!
Hercules Battling the Hydra
Is there a special "torch" or a "golden sword" that we could be using for cutting and treating that would bring better results? Well, it turns out that, like most things, the answer is complicated and there are many opinions.
First, the conditions should be as "optimal" as possible, but defining optimal can vary between experts. One common recommendation is to avoid cutting and treating when there is heavy sap flow such as in May and June, but then many go on to say, "apply any time of year". Other recommendations include avoiding cutting and treating when it is "too hot", during prolonged dry spells, if it is "too cold", too wet or snowy, if precipitation is in the immediate forecast, but details are often vague.
Second, using the "right" herbicide with the "right" method is said to be important for success, but again recommendations vary from one expert guideline to the next.
Here are a few guidelines with some conflicting recommendations:
From the Forest Preserve of Cook County (updated 2022) : https://fpdcc.com/wp-content/uploads/2022/01/FPCC-Volunteer-Herbicide-Manual-010322.pdf. Focusing on the cut and treat sections, here are some of the recommendations:
"Element 4 (triclopyr 4) mixed with Premier ( basal bark oil) is applied to the top of the cut stump and down the sides of the bark to the root crown, but not onto the ground. The bark must be dry; otherwise, the oil won’t make it into the cambium layer. Make sure the bark, cambium, and sapwood are treated." Most others say to just cover the top of the cut stump or the outer one inch edge of larger stumps, but not down the sides to the root crown.
"Advantages: -more effective than basal-bark applications on woody stems greater than 5” in diameter or on thick-barked species -oil-based herbicides do not need to be applied immediately after cutting -can be used in temperatures below freezing." Other guidelines do not include diameter of the stump as being a factor in the effectiveness of cut and treat. Some even claim that basal bark treatment is more effective for all stem sizes. Some specify a lower limit to the temperature when cut and treat is effective rather than just "can be used below freezing".
"Cut Woody Stumps or Chemical Basal Bark Treatments: Includes but is not limited to Honeysuckle, Black Cherry, Maples, Basswood, Tree-of-Heaven, White Poplar, Green Ash, Boxelder, Buckthorns, Barberry, Locusts, Dogwoods, Poison Ivy, Callery Pear, and Autumn Olive. Cut Stump/Basal bark Garlon 4 (triclopyr), 25% Solution, 32 oz/gallon, Must be mixed with basal oil, NO WATER IS ADDED." Others claim that Triclopyr is not consistently effective, especially for honeysuckle, basswood, and cherry.
"Volatilizes at high temperatures and should not be applied over 85F". Others say to avoid using herbicides in bark oil if the temperature is over 65F.
Last a "Phenology Calendar" of specific species is added which recommends cut and treat of common and glossy buckthorn, honeysuckle, and barberry from September through February. Others say cut and treat can be done throughout the year.
Next from the University of Wisconsin Extension.
For both it says: "Cut Stump: Cut a stem of a plant near the base and apply herbicide to the cut surface that remains rooted in the ground. Apply as soon as possible after cutting, but no later than one hour after cutting. Do not use this method if there is heavy sap flow or snow covers the cut surface. Use lower rates on smaller plants and higher rates on larger plants." It then lists 5 different herbicides. For triclopyr it quotes a 90-100% in season and after season effectiveness. Recommended concentration is 20-30%. Timing- Any time of year. A caution listed is- "Overspray or drift to desirable plants should be avoided since even minute quantities of the spray may cause severe injury to plants." Others dispute the claim that Triclopyr is 90-100% effective.
Penn State Extension: https://extension.psu.edu/shrub-honeysuckles
This guideline focuses on honeysuckle. "Stem treatments are effective against invasive shrub honeysuckles and can be applied throughout the year, providing scheduling flexibility. Treatment options include basal bark and stump treatments, which can be done anytime the weather permits, avoiding times when snow prevents spraying to the ground line. If immediate removal of top growth is desired, the preferred approach is to cut the stems close to the soil line and treat the stump. Oil-based (1:4 solution) preparations of triclopyr ester can be applied any time after cutting, while water-based (1:1 solution) treatments using glyphosate or water-based formulations of triclopyr should be applied immediately after the stems are cut."
Management Calendar
Cut Stump | Year-round | Pathfinder II or Garlon 4 Ultra (triclopyr ester) | Ready-to-use or 20%, 1:4 in basal oil | Cut stump treatments with oil-based triclopyr ester herbicides are applied to the cut surface as well as the sides of the stump and can be applied anytime after the stems are cut.p |
Grassland Restoration Network: https://grasslandrestorationnetwork.org/
Just published December 7, 2023. Here is a statement made in this document: "An unfortunate reality is that many invasive shrubs resprout vigorously after a cut stump treatment, and areas often need multiple re-treatments after the initially satisfying (but rather ineffective) cut stump treatment." And that, "In a previous study, I found that only ~30% of resprouting shrubs died from a follow-up foliar herbicide treatment." This success rate is in contrast to most others as above (90-100% success with triclopyr as per the University of Wisconsin Extention), and it goes on to claim that the basal bark method is superior to cut and treat, again contradicting other references.
Purdue University: https://bugwoodcloud.org/mura/mipn/assets/File/ExoticBushHoneysuckleControlTrials.pdf
Cut stump treatment efficacies (of honeysuckle) with 20% triclopyr 4 in bark oil "declined a little in the intermediate size class and significantly in the small size class shrubs. This was due to the increasing difficulty of a chainsaw operator finding and cutting smaller shrubs."
A table lists mortality of honeysuckle as 100% when the plant was over 8 feet tall, 71% 4.5 to 8 feet, and 7% if under 4.5 feet. Success rate with honeysuckle as a function of the height of the plant is not mentioned in any other of these selected references.
Anecdotally, some have said that they "spike" the 20% triclopyr with 2% aminopyrolid (Milestone) to increase the effectiveness, especially for some difficult to control plants.
So, as demonstrated in these selected references, there are many conflicting recommendations for cutting and treating with herbicide for control of invasive shrubs.
For now, Friends of the Blufflands will proceed as follows:
We will favor cutting and treating in the fall to early spring, avoiding times when there is heavy sap flow such as May, as demonstrated (if needed) by cutting a few plants and seeing sap quickly forming on the cut stump.
Absolutely avoid cutting and treating when the when the temperature is over 85F but more optimally when it is over 65F, especially in high quality habitat. We will not have a temperature that is "too cold".
Will avoid times when it is wet, when there is snow cover that would interfere at the cut surface, or if there is precipitation forecasted in the next 4-5 hours.
Avoid when there has been a "prolonged dry period" which will be a bit subjective.
We will continue to use 20 % triclopyr 4 in bark oil on the cut surface close to the ground, but not treating down to the root collar. We will apply enough to the cut surface such that it wicks down the stem slightly.
We will use a more generous amount on large diameter plants while applying only to the outer one inch of the stump.
We will continue to review updates.
The Prairie Enthusiasts is in the process of developing "Best Management Pratices" for cut and treat which will be very helpful.