What Is It?
The larger boxelder leafroller (Archips negundana) is a green caterpillar found on Manitoba maple (boxelder) trees during spring and early summer. The caterpillar feeds on the leaves, webbing them together with silk. If disturbed, the larva quickly drops from the tree, suspended by a silken thread.
What's the Problem? Caterpillar webbing and feeding damage looks unsightly. Dead foliage often bleaches, giving the tree a whitish appearance. Heavy infestations can result in complete defoliation of the tree.
What Can I Do? In most situations, intervention is not required as little tree mortality has been observed. Established Manitoba maple trees that are completely defoliated over several consecutive years appear to recover and continue to grow normally. These trees have the ability to compensate for the caterpillar attack by producing a second set of leaves so that they appear nearly normal by the end of the summer.
If control is desired and the tree is small enough, you can spray for this insect in the spring as soon as you notice damage to the leaves.
Less toxic insecticides registered for the control of leafrollers are bacterial formulations containing BTK (Bacillus thuringiensis sub-species kurstaki).