If insect pests are sucking the lifeblood out of your trees or leaving the leaves in tatters, insecticides are one method to consider when seeking to control the pests. Systemic insecticides work because the tree absorbs the insecticide, delivering a dose of poison to pests that feed on the tree. Systemics can control several common tree insect pests.
Most insecticides work through direct contact with the insect. Either the pesticide covers the insect during spraying, or the insect picks up the insecticide while crawling on the treated plant parts. Systemics, on the other hand, work when the tree absorbs the chemical, usually through its roots or leaves. Trees absorb water through their roots, and that water is pulled up vessels inside of the tree by the evaporation of moisture from the leaves. As the water moves, the insecticide moves with it, poisoning the insect as it feeds on the tree.
Several types of systemics can control common tree pests, according to the University of Minnesota and University of Illinois Extensions. Acephate, disulfoton and imidacloprid control aphids, while imidacloprid also controls adelgids. Acephate works on caterpillars, elm beetles, Japanese beetles, birch leafminer, lacebugs, ash plant bugs, sawflies and scale bugs. Disulfoton kills birch leafminers as well. Always read the label carefully to be sure the systemic you're using has been approved for the tree you're treating.
Because trees take up systemic insecticides, they persist longer in the tree, eliminating the need for repeat applications throughout the growing season. They also will not degrade due to exposure to sunlight or wash off in the rain. Finally, because you cannot contact the insecticide by touching the leaves, systemics pose a lower risk to you, your pets and your family.
Systemic insecticides are applied directly to the soil around the root zone or sprayed onto the leaves, according to the University of Illinois Extension. Insecticides called translaminar systems are applied to the leaves, where they collect inside of the leaves.
Because systemics must move into and throughout the tree, some trees are better suited for them than others. Systemics work best on actively growing trees with extensive root systems, which take up water faster through their roots. Because evaporation from the leaves pulls water up the tree, systemics enter the tree faster on dry, sunny days. In order for the systemic to work, insects must ingest the tissue or fluids containing the insecticide. For that reason, systemics work best on sucking insects that draw directly from the tree's vascular system.