Heavy infestations require spraying with an insecticide aimed either against the adult moths when flying or the larvae in the mines. Several insecticides will control the larvae within the mines. For best control, spray in mid-August after egg hatch. Wettable powder sprays will produce adequate control, however, and are much safer to have and handle in the home grounds. Because moth flights may extend over several weeks, adulticide treatments may need repeating.
Timing is important.
Observe for signs of mite buildup and spray accordingly, or include a miticide in the initial treatment. Many species of tiny wasp parasites have been reared from the larvae of these leaf miners. When widespread outbreaks develop, parasites and other natural factors generally destroy so many of the leaf miners that forest trees are not severely injured. Fertilizing will help to overcome the stress produced by arborvitae leaf miners. Edited in January 1997, based on material developed in 1984.