Pearslug

Pearslug - a sawfly in adult form, the larvae cause leaf damage, commonly on varieties of cherry, plum, pear, cotoneaster and hawthorn.

       
  Pearslug larvae feeding on leaf surface        Pearslugs feeding on hawthorn tree leaves.
Photo: Colorado State University Extension          Photo: Cheyenne Urban Forestry

The larvae are olive-green to yellow-green in color, less than a half inch long and look like slugs covered with a blackish-green slimy secretion.  The larvae feed on cells on the upper part of leaf.  The adult resembling a small, black, thick-waisted wasp, is actually a sawfly.  When a heavy pear slug infestation is occurring, the leaves look skeletonized, becoming dried, and fall off of the tree prematurely.  Most of the heavy leaf damage occurs in late summer, August and into September.  Leaf damage that is done late in the growing season does not affect the health of the plant as much as if it were done early in the season.  Repeated, yearly damage in late summer can stunt plant growth and cause dieback in limbs.  An affected plant can be dusted with wood ashes which will cause the pearslugs to dry up and die.  Insecticides such as Carbaryl can be used to control the pear slug.  Other insecticides can be commercially applied to help control the insect.

Links:

Colorado State University Cooperative Extension

University of Wyoming - Cooperative Extension Service, publication B-1035 is particularly helpful for tree care. This online publication contains information on: Aphids, Borers, Cottonwood blotch leaf miners, Cytospora canker, Fireblight, Gall makers, Aspen leaf spots, Oystershell scale, Pear slugs, Powdery mildew, and Spider mites.