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www.arborage.com ARBOR AGE n SPRING 2015 17 PLANT HEALTH CARE by several factors, such as number of injection sites, diameter of the holes, and the depth. Different injection devices require different number of injection sites, but, generally speaking, most tree injections require multiple injection sites that go around the tree. The injection device that is selected will determine the diameter of the drill bit. Sizes go from 11/64 inch on the small end and up to 3/8 inch on the large end. Regardless of bit diameter, the recommended depth for tree injections is 3/4 inch to 1 inch past the bark. Going deeper causes unnecessary wounding and, worse, can place the treatment past the active conducting tissues, and be ineffective. Utilizing razor-sharp bits can also infl uence the impact of drilling for injections. Just as a dull needle can cause unnecessary injury and possibly compromise the effectiveness of the treatment, dull drill bits can do the same to a tree. Dull bits cause a ripping effect on the vascular tissue, which can not only slow the injection process, but can be more diffi cult for the tree to "heal" over. The reason we put "healing" in parentheses is trees lack a true wound-healing process by means of tissue repair and replacement like you and I do. Instead, when a drill bit creates a wound, the tree responds by compartmentalizing the wound to prevent the spread of decay. This is known as CODIT, an acronym for the Compartmentalization Of Decay In Trees, and was fi rst described by Dr. Alex Shigo in the 1970s. The actual process is biochemically quite complex, but the model is fairly simple. Basically, after any wound that breaks the bark occurs, the tree immediate begins to wall off the tissue around the wound to minimize fungi or other decay organism growth within the structure of the tree. This process has evolved during the past several hundred million years and is how a tree can withstand repeated injection treatments without falling over from decay. Trees can successfully CODIT drill bit wounds as the physical impact of drilling is really no different to the tree as a boring insect wound would be. There are other types of wounding from injection treatments, however, for which trees have not yet evolved a defense. Additionally, because it is hidden under bark, this type of damage often goes unnoticed by the arborist or the homeowner. These injuries When a drill bit creates a wound, the tree responds by compartmentalizing the wound to prevent the spread of decay. This is known as CODIT, an acronym for the Compartmentalization Of Decay In Trees. Maple syrup tap wounds. Trees have no defense against bark separation wounding. CODIT is how trees combat wounding. PHOTO COURTESY OF THE USDA FOREST SERVICE PHOTOS COURTESY OF RAINBOW TREECARE SCIENTIFIC ADVANCEMENTS