Key Features
- Yellow halos leaves
- Circular leaf blisters
- Orange maggots inside
Symptoms
Heavy infestations of boxwood leafminer can defoliate boxwoods by fall and render them unsightly. In late summer and spring mined leaves appear as yellow halos on upper leaf surfaces. Undersides of leaf mines are bumpy to the touch. When mines are cut open in spring orange maggots will be beneath the surface.
Biology
Leaf miners winter inside leaf mines in leaves. In late May adults gnats emerge from leaves to lay eggs into leaf surfaces. Eggs hatch into orange maggots that cause plants to produce bumps between the upper and lower leaf surfaces. Larvae feed all summer until fall.
Management Recommendations
The best control is achieved with a foliar application of systemic insecticide (Abamectin, Acephate, Dinotefuran, Imidacloprid) when adults are flying and laying eggs on tender leaves. This normally occurs when Weigela shrubs are in bloom. If this timing is missed, larvae can be killed inside leaves through mid-July with an application of Imidacloprid or Dinotefuran. Although soil-applied neonicotinoids (eg dinotefuran, imidacloprid) can kill boxwood leaf miners, they are recommended only for cleaning up heavy infestations because they can cause problems with spider mites. The neonicotinoids are usually not a significant risk to pollinators because they are not a rich source of pollen and nectar. Note that the other insecticides listed will only kill adults during flight, and are less effective than the systemic insecticides. Most common and little leaf boxwoods (Buxus sempervirens, and B. microphylla) are susceptible to this insect. Some varieties of B. sempervirens are resistant to this pest including, 'Pendula,' '‘Suffruticosa,' 'Handworthiensis,' 'Pyramidalis,' 'Argenteo-varigata' and 'Varder Valley'.
Effective Pesticides
Active Ingredients include: Abamectin, Acephate, Bifenthrin, Carbaryl, Cyfluthrin, Dinotefuran, Imidacloprid, Malathion, Permethrin, Spinosad
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