Drill and Fill for Tree Injection - Spray Bottles (Husqvarna, Solo), Drills and Herbicide Mixing

Drill and fill is a new alternative to the old tried-and-true “hack-and-squirt” method for injecting herbicide into a tree’s vascular system. Hack-and-squirt uses a small ax to make an incision into which the applicator injects a small dose of concentrated herbicide into each slit. Ergonomically it can be damaging to the user’s wrist and can lead to carpal tunnel problems. See another video on my channel where I demonstrate this method: • Peeling vs. Hack and S...
The advent of modern cordless drills has led to a much improved and more efficient approach whereby the user drills a 1” deep hole at a 45-degree angle and fills it with approximately 1 milliliter of concentrated herbicide. Peter Smallidge, Extension Forester at Cornell, is credited for introducing this method to the northeastern US, but the method has been slow to catch on. Preliminary testing showed that simple trigger-pump spray bottles do not work very well for this treatment, which requires more precision in the volume injected and its direction into the drilled hole than is needed with hack-and-squirt or cut-stump treatments.
In this video, Bob Seymour reviews two high-quality pressurized hand-held spray bottles made by Husqvarna and Solo to deliver a metered dose of chemical into the drilled hole. Keeping the bottle at low pressure is ideal for this work because the user can deliver just the right dosage merely by tapping the button on the top of the handle (instead of squeezing a long trigger). The pointed brass nozzle of the Husqvarna proved to be superior to the Solo which has a larger, more blunt nozzle with no clear point. The pointed nozzle is very helpful in the field to register the tool quickly and precisely into the hole.
Seymour uses his Festool 18-volt cordless drill with a 4 amp-hour battery, equipped with at 5/16” maple tapping bit. A short piece of maple sap tubing is slid over the bit stopping at a depth from the end of exactly 1 inch, giving a hole volume of a bit over 1 milliliter. Holes are drilled at a 45-degree angle downward, and filled with the herbicide as described above. Holes are spaced at a rate of one per 2 inches of diameter (dbh), with odd numbers getting the next largest number. For example, a 2” tree would get one hole, 3” and 4” trees get two holes, etc.
For American beech, we have typically used a 20-25% active ingredient solution of glyphosate in water, dyed purple with a small quantity of RIT dye. We buy the 41% glyphosate Farmworks product from Tractor Supply and dilute it by half. We mix in a one-gallon jug and carry it in a backpack to refill the sprayer when empty. The Husqvarna holds 1.5 liters (about 48 fluid ounces); one gallon will refill this about 3 times. The Solo is smaller at 1 liter, and would probably be the preferred unit if the nozzle were pointed. Perhaps such an option is available; I have not checked.
Clearly these sprayers also have application for foliar treatment because the nozzles are adjustable to create a fan-like pattern or to treat freshly cut stumps where a broader band is helpful. They are relatively economical; we paid less than $30 including shipping for each.