Problem type: Insect
Name of problem: Twolined Chestnut Borer
Plant name(s): Bur oak
Symptoms / Characteristics:
The twolined chestnut borer, Agrilus bilineatus, causes infested trees to exhibit typical symptoms of drought. Dieback usually occurs from the top down. Leaves wilt and turn brown. The insect attacks the vascular system of the tree, inhibiting water and nutrient movement and essentially killing all plant tissue beyond the infection point. Depending on the point of attack, injury or death may range from a single branch to an entire tree. Tree death can occur in as little as one year. Removal of bark from infested stems or branches will reveal tunnels or galleries in which the larvae feed throughout the summer.
The adult beetles are black in color, with two yellow stripes down their backs. Emergence occurs between late May and July as the adults bore D-shaped holes in the bark. The adults can be severe defoliators and will preferentially feed on oak leaves. The eggs are laid shortly thereafter and hatch in about two weeks. The long, narrow, whitish larvae then bore into the stem and commence feeding in the tree's cambium. In late summer, the larvae reach maturity and move to the outer bark for pupation. Damage symptoms from larval tunnelling are typically noticed in late summer.
Control / Preventions:
The twolined chestnut borer typically attacks stressed or weakened trees that may already show signs of decline, therefore it is essential to keep them as healthy as possible. Ensure that the trees always have ample water, but are not too wet. Fertilize regularly, including a high-phosphorus application during periods of drought. Dead or damaged limbs should be pruned and destroyed. Any limbs that are harbouring borers should be pruned such that 2-3 feet of healthy wood beyond the point of attack is also removed. Trees that have been killed by the insects must be removed immediately in order to control the spread of the borer to neighbouring trees. Avoid creating disturbance around the trees. This includes digging trenches, changing the soil level around the tree, damaging the tree with equipment and increasing soil compaction in the root zone.