Plum Fruit Moths [Grapholita funebrana] are a dull grey colour. They are active from late May through until September. Their eggs are normally laid as indiviual eggs on developing fruits. These hatch into larvae/ caterpillars entering the fruit of Plums and Damsons and feed inside the fruit. They are often known as the red plum maggot, as they are pinkish-white in colour. Black frass is left inside and the fruit turns into a gooey mess. Infested fruits also tend to ripen prematurely. The caterpillars eventually emerge and move into bark crevices of the tree in September, some also move into plant debris and soil at the base of the tree . Sometimes a second generation can occur in August-September. They tend to pupate the following spring.
How to control
The first step is to monitor for Plum Fruit Moth activity.They will often host and feed in Blackthorn, their larvae feeding on Sloe fruit. The moths will fly to Plums in late May and be active for most of the summer. To detect their presence put out Plum Fruit Moth Pheromone traps by late May. The pheromone lures in the traps will attract and catch some of the male plum fruit moths. This will give a warning of future damage from their caterpillars and help reduce male moth numbers , which in turn lessens mating.
There is also now a biological control for the Plum fruit larvae/caterpillars when they are not in the fruit. Plum Fruit Killer nematodes can be sprayed on the bark of the Plum Fruit trees and to the base of the trees in September and April. This is when the larvae are present on the tree but not in the fruit. Application of nematodes at these times combined with Plum Fruit Pheromone traps will reduce Plum Fruit Moth infestations.