Thieves sneaking into the orchards of Leonardo da Vinci to steal apples may have been successful once--but not likely twice. Legend has it that da Vinci was so fed up with these impious pome pinchers he devised a way to inject lead arsenic into the trunks of the trees in hopes of poisoning the fruit to, in turn, poison the thieves. If this is true, it not only makes da Vinci a spiteful neighbor who's stingy with his apples, but also makes him one of the first pioneers in the field of tree injection.
There are even earlier accounts, from the 12th Century, of Arabian horticulturalists attempting to inject various compounds into trees in an attempt to alter the fragrance or color of flowers. The success of these trials has been lost to history, but it does show that people have long been interested in the idea that various treatments could be injected into the vascular system and transported throughout the whole tree.
Modern tree injection began in the mid 20th Century and looked to utilize this technology for the benefit of tree health rather than simply aesthetic or apple-orchard-security-system purposes. Just as the advent of the syringe and needle revolutionized the way doctors approach human medicine, the advent of reliable equipment, the formulation of injection-specific chemistries, and a growing knowledge of the science behind tree injection has revolutionized tree care.
Tree injection has many advantages over other application methods. It can be used in situations where spraying the whole tree is not feasible or where soil applications are not an ideal option. There are also certain tree health treatments, especially for the management of vascular wilt diseases, where tree injection is the only treatment that has been shown to be effective. Additionally, in the era of increasing public sensitivity to chemicals in the environment, tree injection also has the positive perception that the treatment is contained entirely inside of the tree, minimizing environmental exposure.
Despite these advantages, tree injection remains a mystery to some, and even controversial to others. There are some disadvantages, of course--with tree wounding and application time at the top of that list--and injection is certainly not a "silver bullet" for every tree problem. Adding to the confusion, a bevy of devices are available to you these days from manufacturers that all claim to have benefits over the others. So how does one know which devices to buy, and in which situations to deploy them?
Tree injection systems and methods
Tree injection can be loosely defined as any method by which a solution is introduced directly into the vascular system of the tree, but there are many ways this can be accomplished. There are passive injection systems, by which a bag of solution is hung on a tree and a series of tubing and tees delivers it by gravity into holes drilled in the base of the tree.
As far as the science of tree injection is concerned, these passive methods work just fine for getting treatments into a tree, but the business of tree injection also requires treatments to be applied quickly as labor costs are often the largest expense of this method. This is one of the reasons that the vast majority of tree injection devices utilize pressure to move treatments into the tree. Depending on the device, this pressure can range from 8 psi upward to 60-70 psi.
Pressure is not the only factor that influences uptake time for an injection treatment. The species of tree has a significant impact, with some trees--such as elm and oak--taking the treatments fairly quickly, while others--such as red maple or white birch--are known to be notoriously slow. The time of year, recent weather, and any tree stress prior to treatment will all influence the time it takes to get a full dose into the tree. An easy fact to remember is that our tree injection treatments are going into the current year's growth ring, so anything that would cause smaller growth rings--such as drought or stress from an insect attack--will have an influence on a treatment's uptake. …