Ash borers During early stages of infestation, the initial damage is low. However, after two to three years of continuous infestation, there's a substantial growth in the population, which disrupts the tree's nutrient and water transport system, resulting in wilting and eventual tree mortality. With favorable hot and dry climates, populations can kill healthy trees quickly. After one to two years of infestation, the bark often falls off, exposing the tunnel-ridden sapwood. They cause D-shaped exit holes along the lower bole surface with frass, filled, zigzagging tunnels are indications of A. planipennis. Within 1/3 to 1/2 of branches dye within the first year, exhibiting a top-down die-back, with the rest of the canopy dying the following year.