What is plum sawfly?
Plum sawfly is a pest, Caliroa cerasi, that causes damage to plums, in particular Czar and Victoria. But it is not specific for plums: its possible host plants include apple, pear, cherry, apricot, hawthorn and mountain ash. The adult plum sawfly – it looks like a glossy black fly – pupates and emerges from the ground in May-June, and lays eggs on the leaves of the fruit tree. The larvae, which are olive green or blackish, feed on the leaves for about three weeks, causing them to turn brown, curl and lose a significant part of their area, eventually becoming skeletons consisting of just the leaf veins. The larvae then fall to the ground and pupate under the soil.
The second generation of the sawfly appears in August and repeats the process. The second generation of larvae drop to the ground, burrow under the soil and spin cocoons about 5-10 cm under the surface.
How to deal with plum sawfly
If you have just a few fairly small plum trees and infestation is light, you can remove the plum sawfly larvae by hand. In case of heavy infestation, it may be necessary to treat the tree with a dilute soap solution – a few drops of washing-up liquid in water, sprayed on every 2-3 days for a couple of weeks – or horticultural fatty acid or oil, that can be purchased at the garden centre.