Systemic products applied to the soil are amongst the most operationally efficient option for the practitioner.
These can be applied at the base of the tree, either by pouring a basal drench solution around the tree or by using soil injection equipment. To the tree these methods are indifferent; the difference is to the applicator. If one is treating several trees at site with the same product soil injection may be faster whereas one or two trees may be faster to treat with basal drench.
Many practitioners will employ a dripline or grid pattern application under the tree but research has shown basal applications to be as effective or better and is markedly easier to apply. The upsides of soil applications are that they are easy to apply with no chemical drift and they have a wide application window. Wounding the tree is not necessary and you get long lasting residual with most chemistries. The downsides of soil application are that they cannot be used in areas of high water tables and you need planning: most soil applied systemic products take weeks to months to reach the canopies of large trees.
Soil applications are ideal for preventative treatments in the fall or spring but may not be the best option for the client that calls in midsummer with insects feeding on their tree right now. In that case you can use one of the other treatment options and then set them up on a preventative treatment schedule for the future.