The borer problem can be aggravated by mesh screen rabbit guards that collect and hold leaves about the trunk, thus providing a more favorable environment for development. Control can be achieved by applying 2 pounds Lorsban 50WP as a butt spray during early June and again mid-August. For best results, drench the burr knot area with a handgun. European Apple Sawfly. Larvae overwinter in the soil, and pupate in the early spring.
Adults emerge and lay eggs between pink and petal fall.
Eggs are laid near the calyx end of the fruit. As the larvae feed, they form a winding borrow just under the skin, leaving a russetted scar at harvest. Uncontrolled larvae can enter a second fruit and borrow into the core. A petal fall spray of Guthion or Imidan usually provides adequate control, but in problem blocks both pink and petal fall sprays may be needed. European Red Mite.