Bolt showing a closed horizontal scar. The same bolt sectioned to show internal condition. In this case, the larva was unable to survive to maturity and damage was limited to staining. The first sign of attack is a wet discoloration on the bark. Later, coarse boring dust and frass can be found exuding from the hole in the bark, or scattered in bark crevices below the hole.
Infestations occasionally cause branch death or sparse crown foliage.
Old borer scars can be classed as horizontal or vertical. The former results when the larva does not complete its life cycle. Vertical scars attest that the larva survived into the second year. Multiple attacked trees are common. These signs appear in all diameters of sugar maple, but they are most pronounced on larger trees.