Lilac (Syringa)-Lilac leafminer

Gracillaria syringella

Pest description and damage The adult insect is a golden yellow moth about 0.5 inch long. The larvae are small, white to pale yellow or greenish caterpillars, 0.125 to 0.25 inch long. The larvae mine leaves during the early part of their development. During later stages of their development, they are also responsible for rolling leaves and skeletonizing them. Privet (Ligustrum), deutzia, euonymus, mountain ash (Sorbus), and ash (Fraxinus) are attacked. Occasionally, lilac leafminer builds to damaging populations but typically, only a few scattered leaves are infested.

Biology and life history Lilac leafminer overwinter as pupae in rolled leaves, or possibly as a larvae in a dropped leaves. Adult moths emerge with new growth and lay eggs along the veins on the underside of leaves. The larvae hatch and commence mining the leaves forming blotches on the leaf surface. When the lavae emerge from inside the leaf, they roll the leaf over their bodies with silk and continue feeding. Later, they select an undamaged leaf, roll it up, and pupate in it. The adult moth emerges about a week later. There may be several generations per year.

Pest monitoring As new growth comes out in spring, watch for the first small brown mines. The larvae in the mines are squashed. Note that the presence of multiple mines in spring could be the harbinger of a heavier leafminer infestation in midsummer and worse in fall.

Management-biological

Often the mined leaf harbors a parasitoid feeding on the lilac leafminer larva and no moths will emerge. There is conflicting information on the wisdom of raking up leaves in fall. While it may remove pupating lilac leafminers, it may also remove the parasitoids.

Management-chemical control

See Table 3 in:

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