What is plum moth?
Plum moth, also known as plum fruit moth, is Grapholita (Cydia) funebrana, and it affects plums, damsons and greengages. The moths emerge in late May and June, mate and lay eggs on the plum tree’s leaves and young shoots. The caterpillars hatch, tunnel into the fruits and feed on the flesh around the stone until about September. These fruits ripen before the others on the tree, and they can often be recognized from resinous material that accumulates on the outside of the fruit. Then the caterpillars emerge, find a hiding place behind a piece of loose bark on the tree, spin a cocoon and spend the winter there.
How to treat plum moth
Plum moth can be controlled by hanging a pheromone trap in the tree in early May, which attracts and catches the male moths. The lure will need to be replaced by early July to make sure the plums stay grub-free. The pheromone traps can be removed from the tree at the end of August. Birds may try to enter the trap: this can be prevented by adding netting over the two ends.
The trap will show you how serious the problem is: if there are just one or two moths inside it by the end of July, the problem is not too bad. If you trap many more moths, it may be necessary to use other techniques of control. Identify and remove infested fruits, and dispose of them definitively (do not compost or recycle). A winter wash can be useful to remove the overwintering larvae.