There are a number of ways to treat trees for Japanese beetles, but some of it depends on the size of your tree. Is it a tall tree or small recently planted tree? Small trees are easier to manage Japanese beetle populations without pesticides because you can reach most of the tree. Shaking the beetles off into buckets of soapy water in the morning before work and again after work helps reduce pressure. This must be done religiously throughout the flight (mid-June through the end of August) of the beetles to have the best efficacy. Planting trees that Japanese beetles do not like is another option, but they feed on over 300 different species of plants. Some trees they do not like include oaks, red maple, tuliptree magnolia, hollies and ashes. Other options are to purchase a backpack sprayer and insecticide and spray the parts you can reach with the sprayer yourself while wearing the necessary protective equipment. There is also a systemic product available however it is a neonicotinoid and there has been increased concern about bee safety with its use. Additionally, the beetles need to eat some of the plant to get exposed to the insecticide. Another option is to have a professional treat your trees.