Problem type: Insect
Name of problem: Spruce Needle Miner
Plant name(s): White, Engelmann, Norway and Colorado blue spruce
Symptoms / Characteristics:
Needles are hollowed, severed and woven together with silk webbing. These nests of dead needles and webbing are typically located at the base of large branches.
Defoliation is due to larvae of the moth Endothenia albolineana. The adults emerge during May and June at which time the females lay eggs along the base of needles. When the larvae hatch, they bore into the base and tunnel their way up to the tip, feeding on the interior. Initially the larvae feed on one side only, but consume more of the interior as they mature. A mass of dead needles and frass (droppings) becomes a nest in which the larvae overwinter. The nests also trap dust and airborne debris, which impairs vigour, and decreases aesthetic value of the plant. Defoliation weakens the tree and renders it susceptible to secondary insect and disease pests. Prolonged infestation may eventually kill the tree.
The larvae are green with dark brown heads, and may reach a mature length of 8 mm. The adults are grey and brown moths with three irregular bands of white on their forewings. Other species of needle miner have been known to attack spruce, pine and fir trees.
Control / Preventions:
A high pressure garden hose can be used to wash away nests before bud break in the spring. Fallen nests must then be collected and burned. However, this method may not fully eliminate an infestation. Pruning heavily infested areas may also be required. Dimethoate may be used as a chemical control in accordance with manufacturer directions and precautions.