The Shigometer as Predictor of Bronze Birch Borer Risk

Abstract

Experiments were conducted during 1981 to determine if borers concentrate their attack on certain trees and if the Shigometer might be used to separate these trees from the rest of the population. Twenty European white birch (Betula pendula) representing different stages of dieback were used. Pyrethrum was applied to the tree crowns on alternate days and the stunned adult bronze birch borers were collected. Emergence from each tree was also recorded. All trees exhibiting symptoms attracted adults and had emergence. Three trees that exhibited minor flagging or no symptoms also attracted adults to their crowns, but no emergence was observed. The Shigometer was a reliable measure of susceptibility to borer attack. All trees that were attacked gave readings in excess of 12 kohms, regardless of crown appearance.