How it works

Solutions can be injected into the xylem (the water-conducting vessels within the wood) because the pressure inside of the xylem is less than the atmospheric pressure. This is due to water being lost from the canopy to the air, causing negative pressure in the xylem. This negative pressure draws sap up from the roots. An exception to this is in late winter and early spring when the buds are expanding. At this time sap is actually being forced upward from the roots to promote the expansion of buds. This is when trees are tapped to gather sap for making sugar and syrup.

    Injection into the trunk of a tree works best when the canopy is fully leafed out. It can still be done in the Fall, although the rate of uptake will be slower. During the summer the rate of uptake can vary with the health of the tree, soil moisture, and weather conditions. Higher temperatures and wind will increase water loss from the canopy and the rate uptake will be faster. Trees may shut down stomata (pores on the leaves) during drought conditions, so this would decrease the rate of uptake. Vigorous trees often have larger growth rings, which means larger xylem vessels that can move sap and injected solutions faster.

Why inject instead of other methods of application?

Injection places the solution directly into the tree. This eliminates concerns of overspray or drift from spray applications. It also reduces the risk of groundwater contamination. At some properties, tree injection may be the only treatment option due to proximity to water or other sensitive areas.

    Less material is used when injecting. By placing the material directly inside of the tree, less of it is lost to run-off, drift, or evaporation. Pesticides reach an effective dose in the plant quickly and often protect the tree longer when injected as the material inside of the tree is not exposed to rain that could cause run-off or sunlight that could break it down.

    Some diseases such as oak wilt or Dutch elm disease can not be effectively treated by spraying. These fungi grow inside of the xylem and injection puts the fungicide where it is needed.

Tips for trunk injection of trees

To get the solution into the xylem it is necessary to drill through the bark and a short distance into the wood. It is not necessary to drill deep into the trunk as most of the sap movement is in the outer growth rings.

    The fastest-growing part of the trunk is where the buttress roots flare out from the base. Since this is the fastest-growing area, the xylem vessels will be the largest there. Injecting into the buttress flares usually results in the best uptake. Since this is the fastest growing area of the trunk the holes drilled here will heal faster than holes drilled higher up. We use ¼ diameter drill bits with our Tree Defend Injectors and it is often difficult to see where the holes were drilled after a couple of growing seasons.

    Since the pressure inside of the xylem is less than the atmosphere once the trees have leafed out, you don’t need high pressure to get the solution into the tree. We usually have good uptake with only 15 to 25 psi. The negative pressure inside the xylem also prevents the solution from running back out of the holes. It is being drawn into the tree.

When dealing with oak wilt I advise sealing the drilled holes with an appropriate wound dressing to prevent beetles from accessing the holes. With other species, I advise leaving the holes to air dry and close naturally as the tree grows.

What conditions can be treated by injection?

Tree injection has been used to treat a wide variety of insects, mites, fungi, bacteria, and other diseases. Injections can be especially useful in the treatment of borers such as emerald ash borer, bronze birch borer, and bark beetles since these insects feed underneath the bark. The injection is often relied upon for the control and prevention of Dutch elm disease and the prevention of root transmission of oak wilt. Phytoplasma diseases such as lethal palm yellows are controlled using injections of tetracycline solutions. It can also be used to administer nutrients, hormones or bio-stimulants to correct nutrient deficiencies or support trees stressed due to environmental conditions.

    Tree injection has been an important tool for arborists and foresters for some time. As concerns about the environmental effects of other application methods emerge and new pests and diseases spread the importance of tree injection will continue or increase.