What is apple sawfly?
Apple sawfly is a flying insect, scientific name Hoplocampa testudinea, that lays its eggs on apple blossom. The insect is about 5 mm long and brown in colour. The larvae hatch soon after petal fall, burrrow into the fruitlets, and begin to consume it from inside, making large holes and often moving on to another fruit. The fruit may fall from the tree in June. Fruitlets only marginally attacked may stay on the tree and develop to maturity, though they often have a long scar that reveals the path of the larvae, initially just under the skin of the fruitlet. In late June or early July, the larvae descend to the ground, enter the soil and create a cocoon underground. They overwinter in the cocoon, pupate and emerge next spring. Some varieties, notably Charles Ross, Discovery, Ellison’s Orange, James Grieve and Worcester Pearmain, are particularly susceptible to apple sawfly. Usually, when fruit set is heavy, a light presence of apple sawfly is not a problem. In years with only a light fruit set, things are worse.
How to treat apple sawfly
In late May and early June, remove and safely dispose of fruitlets that have been damaged – you will see the holes with the blackish-brown waste material produced by the larva.