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Red sphere hung from a tree branch

A red ball "sticky trap" useful for monitoring apple maggot, a pest of plum.

Insect Pests

Plum curculio, a snout weevil, attacks young fruitlets as they begin to grow to size of one-half inch in diameter.  The plum curculio adult lays eggs directly into the fruit during a period of 5 to 7 weeks after bloom.  In the process of egg laying, the curculio creates a ¼-inch crescent shaped scar on the fruit surface. Infestation leads to fruit drop in most cases, so orchards that are not protected by insecticide can lose a considerable number of fruit to this pest.  Protectant sprays begin at or after petal fall and continue into July.

Apple maggot occurs in abundance in the northeast.  Adult flies lay eggs in fruit in summer, so damage occurs because of fruit larvae feeding within ripening fruit.  Traps, red spheres coated with a layer of sticky gel called Tangletrap™, can be used to monitor populations and to measure when thresholds are reached.  Because populations vary from orchard to orchard, traps can be used to determine when insecticides are most effective or not needed.  Populations are most abundant near unsprayed apple trees. 

Spotted wing drosophila, a fruit fly, can attack ripe fruit. Avoid leaving fully ripe fruit on the tree or in the orchard to minimize damage.  Insecticides applied for apple maggot may also protect fruit from spotted wing drosophila. 

Other pests are likely to be present in the orchard, and are generally managed by insecticide sprays applied to control plum curculio and apple maggot.