Lauri Jean Crowe defines pear slugs, or caliroa cerasi, a troublesome cherry tree pest as well as an attacker of many other stone fruit trees.
What Is It?
Cherry tree pear slugs are known as caliroa cerasi. Caliroa cerasi closely resemble your run of the mill slug, but are actually the larvae of the black-and-yellow sawfly. These pesky insect pests are troublesome not only to cherry trees, but also to other stone fruit trees such as the pear, plum and also a range of ornamental trees. At the most extreme case of pear slug damage the entire cherry tree may become defoliated and have a low yield of stone fruits which are of an extremely poor quality.
What Does It Look Like?
Cherry tree pear slugs of the caliroa cerasi species are orange worms. They are sluglike and range in size up to ½ inch in length. Occasionally the cherry tree pear slug will be a dark, almost forest green color which can make it difficult to spot in areas of dense foliage, however the majority are an orangish brown shade. Pear slugs are extremely wet worms which gives them a shiny appearance. Damage from cherry tree pear slugs occurs most often in the upper leaves of the trees and migrates downward. The upper surfaces of the cherry tree leaves may have a chewed appeareance, as if they are being eaten between the leaf veins, which they are. This feeding pattern can leave a lacy layer of tissue which begins as translucent and quickly turns light tan to brownish in appearance. As the leave turn brown they often drop off the tree entirely. Cherry tree pear slug damage may also result in a low fruit yield with poor quality of stone fruits. A heavy infestation can quickly weaken a newly planted cherry tree and cause it to die off.
How Does It Manifest?
Cherry tree pear slugs are the larvae of the black-and-yellow sawflies which are predators of stone fruit trees and some ornamentals. Adult sawflies appear in the late spring at which time the females lay their clusters of eggs on the leaves of the cherry tree. Within a matter of weeks the larvae hatch from the eggs on the cherry tree leaves and begin to feed on the foliage. The cherry tree pear slugs emit a slimy, olive green substance which gives them the appearance of shiny, slugs. It is this material that the larvae exude which makes some of them appear dark green rather than the more common orange. The amount exuded can affect coloring because of its adherance to the larval body. Cherry tree pear slugs feed on the leave foliage for approximately one month's time at which point the pear slugs drop to the ground and burrow into the soil. The cherry tree pear slugs then pupate in the soil and later emerge as adult black-and-yellow sawflies to begin the reproducing and feeding cycle again.
What Can I Do About It?
There are many insecticides available specifically for use on sawflies and their pear slug larvae. You can find them labeled for use on sawflies, black-and-yellow sawflies, or pear slugs. All are effective on these pesky insects, but are simply marketed differently in regions which may call them pear slugs vs sawflies, etc. You will find these preparations in a spray formula and should apply them as soon as you notice pear slug damage on your cherry tree. These insects are tenacious, so you may have to respray more than once to get the populations under control. Follow the label instructions for your region.
