Provided are a tree trunk injection whereby pathogenic fungi and/or insects in trees can be effectively controlled merely by a short-time application in a low chemical dose, and a method for controlling tree diseases using the tree trunk injection. According to one embodiment of the present invention, the tree trunk injection is obtained by adding, to an aqueous solution of an insecticidal component such as acetamiprid, a hardly soluble fungicidal component such as thiophanate methyl so as to suspend the hardly soluble fungicidal component in a volume-based 50% particle diameter of 4 µm or smaller, or adding thereto at least one fungicidal component selected from the group consisting of triflumizole and metconazole.
