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Boxwood Leaf Miner
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Taken from the B.Y.G.L. (Buckeye Yard and Garden Online) Newsletter
Contributing Authors: Pam Bennett, Joe Boggs, Cindy Meyer, Jim Chatfield, Erik Draper, Dave Dyke, Gary Gao, David Goerig, Tim Malinich, Becky McCann, Bridget Meiring, Amy Stone and Curtis Young |
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Joe Boggs reported observing significant damage to boxwood leaves in southwest Ohio caused by the boxwood leaf miner (Monarthropalpus flavus). Although the damage was highly localized, Joe noted that it could easily be mistaken for winter injury. The leafminer is a non-native midge fly that was accidentally introduced into North America from Europe. BYGLers discussed the distribution of the leafminer in Ohio and agreed that the fly is common in the southern and central parts of the state, but rarely observed in the northern part of the state.
Adult boxwood leafminers superficially resemble miniature mosquitoes; however, they have bright orange abdomens. Adults are on the wing when the accumulated growing degree days reach 440, which is the same time red horse chestnut is in full bloom and just about the time doublefile Viburnum is in full bloom. |
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Once the females are mated, they use their sharp ovipositors to insert eggs between the upper and lower leaf surfaces of boxwood leaves. Several eggs may be laid per leaf. The resulting yellowish-orange larvae (maggots) spend the remainder of the season developing through the 1st and 2nd instar stages as they consume interior leaf tissue to produce blister-like mines and. Winter is spent as 3rd instar larvae inside the blister mines. In the spring, the larvae resume feeding and they develop through a 4th instar stage. During this time, mines expand rapidly, and damage becomes evident. Indeed, as mined leaves turn from yellow to orangish-brown, the leafminer damage mimics winter injury.
Effective control options for this leafminer involve applications of neonicotinoids such as imidacloprid (e.g. Merit and generics); clothianidin (e.g. Arena or Aloft); and thiamethoxam (e.g. Meridian). An application this spring when new leaves are around 1/4" long will prevent damage during the upcoming season by killing 1st instar larvae. An application of imidacloprid made in October will kill the 3rd and 4th instar larvae next spring. The fall application does not prevent damage from 1st and 2nd instar leafminer larvae. However, it will carry the added benefit of controlling BOXWOOD PSYLLID (Psylla buxi) before these aphid relatives produce their characteristic leaf-cupping damage. |
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