Chemicals into Trees Part II

Getting Chemicals Into Trees Without Spraying
Part 2: Soil Injection/Drenching and Trunk Basal Spray

          Soil injection system involves injecting
                   chemicals 2 to 4 inches deep.

Chemicals are applied to trees to repel or kill damaging insects, to treat or prevent fungal diseases, to give nutrients, and to kill sprouts, stumps, or even entire trees with herbicides. Spraying is the most typical way to apply these chemicals, but it sometimes isn’t appropriate.

Chemicals can sometimes be placed inside trees or gotten inside easily, which is what we’ll cover here. In the last article we covered trunk implantation and trunk injection. In this article we will cover soil injection/drenching and trunk basal sprays. We also will present a recap of all of the methods and give some guidelines for which option to choose.



Soil injection or drench methods involve placing chemicals in liquid form in the soil near the roots. As with the other methods, the chemicals must be water soluble. Chemicals should be applied to moist but not saturated soil. Chemical application timing varies depending on the chemical and the pest. This is used for application of imidacloprid, dinotefuran (Safari), and some growth regulators. The high pressure equipment needed for soil injection is expensive.

Soil injection methods typically involve injecting chemicals 2 to 4 inches deep with a high pressure injector either within 18 inches of the trunk or on a grid. The amount to be applied depends on trunk diameter, with additional trunk diameters added if multiple trees are being treated in an area. Soil injection of dinotefuran has been used in Utah recently for control of black pineleaf scale, and it has been quite effective.

With the soil drench method, you simply pour chemical mixed in water on the soil near the tree’s root crown. Mulch or other surface organic matter is pulled back and the chemical is poured directly on mineral soil. The mulch is then replaced. The amount of chemical used is based on inches of trunk diameter and will be stated on the label. Chemicals used would be similar to the soil injection method.

With soil injection and drench methods the trees are not wounded but presumably somewhat higher amounts of chemicals must be used than with trunk injection (though maybe less than with spraying). Also, there is a higher possibility for affecting non-target insects. The soil drench method uses almost no tools. Uptake may be slower than with trunk injection, and it is critical that the chemical be water soluble.


Trunk basal sprays saturate the lower 5 feet of the trunk.

Trunk basal sprays involve spraying, but the chemical is applied to the trunk base and is absorbed through the bark and then taken up in the vascular system. The chemical is sprayed on the lower five feet of a dry trunk, saturating the bark.

Chemical uptake occurs through bark. The method is fast, equipment is simple and fairly cheap, there is little chance for spray drift, and no holes are required. Dinotefuran (Safari) can be applied with this method for control of black pineleaf scale and other pests.

Imidacloprid also has been applied experimentally with this method, but it currently is not labeled for such use. Check the label for allowable uses for your state before you purchase or apply a chemical. Labels frequently change, so check each time you use a chemical.


Deciding which of these chemical application methods is best depends on your circumstances, the tree’s circumstances, and the target pest or nutrient used. Methods that do not harm the tree, especially if they are done repeatedly, should be chosen first. Simplicity and low cost also are important. Trunk basal spray and soil drench meet these criteria, as does soil injection if the equipment is readily available.

Injection without a drilled hole (i.e. ArborSystems Wedgle Direct-Inject system) seems attractive at first glance, but equipment is expensive and, more importantly, the bubbles formed during the injection can cause significant wounding. Therefore, these systems should be used with caution. If non-injected methods are available, they should get priority. Repeated injection treatments (e.g. yearly) should be avoided.

Injection and implantation are most useful where soil access is limited or extensive root damage may have occurred. Even then, a trunk basal spray would likely work, assuming the product is labeled for the pest and for that type of application.


Use of trade names and specific product examples is not meant to imply endorsement of certain products. Always read pesticide labels and follow directions.

For a complete fact sheet on this topic go to and click on fact sheet #20.

-By Dr. Michael Kuhns, Extension Forestry Specialist, Wildland Resources Department, Utah State University Cooperative Extension, Logan. Kuhns maintains a very informative website at