Planting the right trees and removing the wrong ones can both be part of effective deer habitat management. You might need to remove trees for timber stand improvement (selecting low-value tree species to allow sunlight and other resources to go toward understory growth or other high-value trees) or to control non-native invasive tree species that are consuming space that could be occupied by valuable native plants.
One of the simplest and most effective techniques for removing select trees and large shrubs without cutting them down is called the “hack-and-squirt” method, or bark injection. Quite simply, a manager hacks small cuts in the trunk of target trees and squirts an herbicide solution into the cut. “Cut-and-treat” is another method in which the entire tree or shrub is cut down with a chainsaw and the stump immediately painted with herbicide.
“The real plus for injection and cut-and-treat is you target the plants you want to control and you leave those you want to encourage, and there are probably no safer methods of treatment than these two,” said Dr. Jim Miller, a research ecologist and team leader at the G.W. Andrews Forestry Sciences Laboratory in Auburn, Ala. Jim is also a co-author with Dr. Karl Miller of the book Forest Plants of the Southeast and Their Wildlife Uses.
Girdling, or chopping a deep ring completely around the trunk of a tree to cut off circulation, was for decades the best method for killing unwanted trees. However, Jim said, girdling only kills the tree above the ring, and many species are very good at coming back from rootsprouts. “You can actually multiply your problem by just girdling or cutting down the tree,” said Jim, “especially with invasives like tree of heaven, chinaberry or privet. That’s why herbicides are best.”
The Hack-and-Squirt Method
“Hack-and-squirt is a very simple method,” said Jim. “If a tree has a main stem, merely place cut marks around it and inject the herbicide. However, how you make those cuts is important.”
To start with, use a sharp tool such as a machete, brush axe or hatchet. Chop into the trunk at chest height, being sure to penetrate the cambium layer below the bark. The cut should form a “cup” that will hold the herbicide. If the bark splits on either side of the cut, or if the angle of the cut is too shallow, herbicide will leak out. This will not only reduce the effectiveness of the application, it could kill nearby non-target plants if the herbicide is soil active and is washed into the soil by rain.
With the blade still in the cut, twist the blade downward to open the cut and spray 1 milliliter of herbicide mix from a common spray bottle into the cut. All utility spray bottles conveniently deliver 1 milliliter per trigger pull.
The number of cuts made in the tree will vary depending on the herbicide used. Always read the label for appropriate dosages, cut spacing, and mixing instructions. For large trees requiring multiple cuts, space the cuts evenly around the trunk. For trees and shrubs with multiple trunks, be sure to treat every trunk.
“All herbicides are effective on a certain number of species,” said Jim, “but fortunately the new ones like Arsenal AC have a wide range of effectiveness and can be used at low concentrations and wider cut spacings. That has been a real plus to this method. With Arsenal AC, we’ve gone to wider spacings, which means a lot less time at the tree and a lot less energy expended.”
Arsenal AC calls for one cut per 3 to 4 inches of tree diameter at breast height (DBH). So, a 4-inch diameter tree would need one cut. The mixing rate for Arsenal AC is 10 percent, or one part herbicide to nine parts water.
Keep in mind that Arsenal AC is soil active and can injure or kill non-target plants if accidentally spilled or washed off equipment near desirable plants.
Two other herbicides used widely for bark injection are Garlon 3A and 2-4,D Amine, although Arsenal AC seems to have the widest range of species effectiveness. With any herbicide, consult the label for a list of species that are killed by the product. Every herbicide is better at killing some species while less effective on others. Also be sure to wear appropriate clothing and protective equipment as recommended by the label.
When Hack-and-Squirt is Effective
“This method is effective almost any season except early spring,” said Jim. “When you have that heavy sap flow and sap rise, it can wash the herbicide right out of the cut. Otherwise, late winter, summer and fall are fine. In the South, the sap starts flowing in March or into April. It will start later in the North.”
Another timing factor is rainfall. Do not apply herbicide if rainfall is forecasted. Rainfall within a day or two of the application can wash the herbicide out of the cut.
About Root Grafting
A concern with injecting herbicides is root grafting — trees of similar species often have interconnected roots, and injecting one can kill the other. This is only a concern if you are using bark injection to thin desirable species, such as oaks, according to Jim.
“Root grafts are usually species-to-species,” he said. “Usually you don’t have to worry about that when treating invasives. I’ve seen damage to non-target species in a mixed stand, but it’s usually considered to be a result of a soil-active herbicide washing from the cut into the soil, or using too much herbicide.”
Again, consult the label of the herbicide and follow instructions closely. Guidelines should help you avoid potential harm to non-target species.
The Cut-and-Treat Method
When it comes to shrubs or trees with multiple trunks, or dense infestations of shrub species like privet, it can be challenging to inject every trunk or even to find room to swing a hatchet for making cuts. This is when the cut-and-treat method is a good alternative. This simply involves cutting down a tree or shrub with a chainsaw, making the cut as close to the ground as possible. Immediately afterward, the stump is painted with herbicide.
“The key is immediate treatment,” said Jim. “The stump will only absorb the herbicide for a very short period of time.”
Herbicide should be brushed onto the outer edge of the stump, where the circulatory layers are located. For smaller stumps, the entire surface can be painted without wasting herbicide. Some experts like to mix a dye with the herbicide so they can see which stumps they have painted, especially when stumps are numerous in a small area, but dyes can be expensive, Jim said.
As with hack-and-squirt, this method is not effective in early spring when the sap is rising. If stumps resprout after treatment, a contact herbicide such as Roundup (glyphosate) should be applied to the foliage.
For timber stand improvement, if you aren’t experienced identifying trees, talk to your local state agency forester for advice on selecting species with little wildlife or timber value. A terrific resource on the Internet for identifying and dealing with invasive species is found at www.invasive.org. Numerous publications, such as Invasive Plants of the Eastern United States, are stored on this site and include links to high-quality photographs of invasive species in all regions.