A small greenish worm is eating the foliage on my cherry tree. What should I do?

FAQ
Question: 

A small greenish worm is eating the foliage on my cherry tree. What should I do?

Answer: 

The greenish worm is probably the pear slug.  The pear slug is not an actual slug.  It’s the larval stage of an insect (sawfly).  The pear slug feeds on pear, cherry, plum, and several other woody plants.  

The slug-like larvae are yellow but usually appear olive green or black because of a covering of secreted slime.  The mature “slug” is about 1/4 to 3/8 inch long.  Larvae feed on the leaves for about 4 weeks.  When full grown the larvae drop to the ground, burrow into the soil, and pupate.  Adult sawflies emerge in May and June (first generation) and late July and August (second generation).  After mating, female sawflies insert eggs into the leaf surfaces of suitable plant hosts.  The eggs hatch in 1 to 2 weeks.  

The larvae feed on the upper surface of leaves, eating the tissue between the leaf veins, but leaving the veins themselves.  (This feeding pattern is known as skeletonization.)  Leaves that are heavily fed upon by the larvae turn brown, as only the veins and a thin layer of tissue remains on the leaves.  Heavily damaged leaves may drop from the tree.  Fortunately, pear slugs seldom cause serious damage to healthy, well-established trees.  If you wish, pear slugs are easily controlled with insecticidal soap, neem oil, bifenthrin, carbaryl, malathion, permethrin, spinosad or other general landscape insecticide sprays. 

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