Phyllonorycter spp.

 

HOST Aspen, poplar, cottonwood

DAMAGE/SYMPTOMS The caterpillar feeding and mining cause white blotches on the underside of the leaves. Heavy outbreaks can cause reduced tree growth and branch dieback.

LIFE CYCLE Adult moths emerge from overwintering sites and feed on nectar. Females mate and deposit several eggs on newly emerging leaves. The larvae develop and feed within the leaf, causing blotchy looking tissue. They pupate, and the adults emerge in late summer as leaves are starting to senesce.

MANAGEMENT The leafminers attack stressed trees. Normally, no treatment is necessary, and the pests are controlled by natural enemies later in the summer. Keep aspen and cottonwood trees well cared for with frequent watering. Pick off the mined leaves and dispose of them (if there are only a few—sometimes this leafminer can be found on the majority of a tree’s leaves). Rake up and dispose of leaves in the fall to reduce overwintering populations of the moths. Chemical controls are only moderately effective in controlling the pest and have sometimes made the populations worse by killing many of the natural enemies of the caterpillars. If insecticides are necessary in the future, they are most effective at the egg-laying stage of the moth (right after the tree leafs out). Products that could be used include those with the active ingredients spinosad, permethrin, bifenthrin, carbaryl, and zeta-cypermethrin. Systemic insecticides (active ingredients such as imidacloprid and dinotefuran) are not effective against larvae.

 

A Aspen blotch leafminer damage.

 

Aspen blotch leafminer mines on the underside of a leaf.