Spraying for worms in peach trees helps protect the peaches and the tree from larval insects that damage and weaken the tree in addition to spreading disease. Applying the spray at the right time makes the pesticide more effective.
Preventive sprays applied in early spring kill off any eggs and insects that will be laying eggs, so early spring applications reduce the population of worms and larval insects before they can do damage. Spraying while the tree is still dormant protects new growth from damage by the pesticide.
Spraying when the tree is in bloom, before the petals have begun falling from the tree, protects the peach tree from various insects, fungi and worm-like larvae. Pesticides applied during this time target a different problem than an earlier application.
Spraying after the fruit have formed a husk and before the harvest helps to control a variety of insects and worm-like larvae, including Japanese beetles. Using pesticides during this time protects the fully formed fruit from damage and keeps the harvest healthy.