Arborvitae Leafminer damages Arborvitae plants by causing leaf browning and premature foliage loss. The damage is caused by the tiny larvae of several different moth species which tunnel inside the leaf tissue of Arborvitae plants.
An infestation of Arborvitae Leafminer will not only cause Arborvitae plants to become unsightly, but the plants will lose their effectiveness as a screening plant. Arborvitae plants continually damaged by Arborvitae Leafminer will become more susceptible and attractive to other pests such as spider mites.
LIFE CYCLE OF ARBORVITAE LEAFMINER
Eggs are laid on the current years’ growth in early to mid summer. Upon hatching, the larvae burrow into the foliage and begin feeding on the interior leaf tissue of the Arborvitae plant throughout the remainder of the summer and fall, and resume feeding in the spring. The larva pupates and hatches into an adult moth in the late spring to start the cycle over again.
SYMPTOMS OF ARBORVITAE LEAFMINER INFESTATION
Foliage from the prior years’ growth will turn yellow to brown in color in late spring to early summer. If the Arborvitae is reasonably healthy new growth will be produced in the spring and will be green. Damage is most severe on the lower half of the plant and on the interior foliage.
To confirm the presence of Arborvitae Leafminer carefully tear open the brown foliage. The center of the foliage will be hollow and dark brown to black frass (larval excrement) will be present. In some instances the larva, which is a very tiny caterpillar, can be found.
Arborvitae Leafminer damage is sometimes mistaken for winter desiccation damage. The primary distinction between the two disorders is that winter desiccation damage will affect the outer foliage and often only the foliage on one side of the plant. Arborvitae Leafminer damage will be on the prior years’ growth and will be on all sides of the Arborvitae plant.
CONTROL OF ARBORVITAE LEAFMINER
Arborvitae Leafminer damage can be reduced with tree spraying treatments or soil injected insecticides. Tree spraying treatments will require two treatments per year, one in late April to early May and a follow-up treatment in late August to early September. Soil injected insecticides can be applied either in the fall or the early spring for season-long control.
Proper maintenance practices will make Arborvitae plants less attractive to Arborvitae Leafminer and will help infested plants recover quicker. Apply supplemental irrigation using a soaker hose or drip irrigation system during the hotter, drier periods of the summer. Keep plants mulched with a 2 – 4 inch layer of composted wood chips. Fertilize plants periodically to maintain healthy, vigorous growth.