Soil injection of imidacloprid (Merit) is the preferred application method for protecting ALB host trees that are at risk of infestation. Thousands of trees are injected each year in New York and Chicago, but more trees could be protected and cost per tree could be reduced if there was a longer application time-frame. Maple and Ash street trees in Chicago were treated in the Fall before and after leaf drop, as well as in the Spring (typical application). One set of trees was treated and sampled for two years in a row, another set was treated and sampled for one year. Xylem sap was extracted from leaf bracts and subjected to an ELISA analysis for the presence of imidacloprid. Residue comparisons were made between and within tree species, as well as between one-year and two-years of treatment.