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Leafminers (LM)

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Phyllonorycter crataegella, P. blancardella

Overview

Apple blotch leafminer and spotted tentiform leafminer hosts include apple, pear, cherry, plum and quince, favoring apple leaves.The first 3 larval instars feed on tissue between the two epidermal layers of the leaf causing a translucent, 'sap feeding' mine that is visible only from the underside of leaf surface. The last 2 instars feed more extensively on leaf tissues and their 'tissue feeding' mines are visible from both the top and underside of leaves. 'Tissue feeding' mine on upper leaf surface contains numerous white dots.

Biology

  • LM overwinter as pupae within mines on fallen leaves.
  • Adults emerge in late April to early May and deposit eggs singly on leaf underside. Adults are 3/16 inch long, light brown moths that appear shiny in flight, with white spots that look like transverse bands when wings are folded. ABLM is nearly indistinguishable from STLM, but has forewings that are usually smaller and less heavily marked with white scales than STLM.
  • Eggs hatch in 5-16 days and feed just below the lower leaf epidermis as 'sap feeders'. By late May larvae begin feeding just below the upper leaf epidermis, producing densely spotted mines visible on the upper leaf surface.
  • There are 3 generations per year.

Monitoring

  • Insecticide applications against 2nd generation mines normally not necessary unless mines exceed 1mine per fruit cluster leaf during 1st generation (by early June).
  • Spur and leaf sampling for 2nd generation sap feeding mines allows effective timing of spray applications. Best time for insecticide application is when earliest 2nd generation mines are visible from the upper leaf surface (less than 10% have advanced to tissue feeding stage).
  • Two parasitic wasps commonly attack LM larvae and can be found inside tissue feeding mines. Level of parasitism required for adequate LM biological control LM is unknown. Being aware of parasitoid development and behavior in orchards may aid in LM management.

Management

  • If needed, spray insecticide when 2nd generation mines begin to advance to the tissue feeding stage. Selective insecticides allow parasitoids to substantially reduce larval populations.
  • Second insecticide application may be needed.