The plum curculio is one of the most difficult fruit tree pests to control, especially in peaches. It is a small insect, about 1/4 inch long. The females make small crescent-shaped slits in the peach skin and lay their eggs under the skin. The larvae, which are small grayish-yellow grubs, migrate to the area near the pit, where they destroy the peach fruit from the inside. Synthetic insecticides have been the weapons of choice among commercial peach growers for economic reasons, but some of these have been made illegal and safer options are being adopted. There are several things that can be done to control the plum curculio organically, and they give excellent results in organic orchards and for home fruit trees.
Clean up and burn all cut prunings, damaged wood, dropped fruit and other debris from around peach trees. Good orchard sanitation is the best way to prevent plum curculio infestations, because they shelter and overwinter in debris and tree bark. Prevention is always more effective than treatment.
Mix carbaryl or malathion in your sprayer, following the instructions and mix ratios exactly. These are synthetic chemical poisons which are used in commercial applications, and they are not an organic remedy. The chemicals are not a one-time solution; they must be part of a regular, ongoing spray regimen. Either of these chemicals requires a 7- to 10-day waiting period between spray and harvest.
Use an organic spray instead of a synthetic chemical treatment. Mix an organic spray pesticide, such as Green Light Fruit Tree Spray, according to the the manufacturer's instructions. The active ingredients in this spray are neem oil and pyrethrins, and it is labeled for use against plum curculios. Apply the spray as directed, covering the entire tree.
Organic garden supply centers also sell neem oil and pyrethrins individually for use on other crops. If you have neem oil and pyrethrins for other garden purposes, you can follow instructions on the individual packages to make your own fruit tree spray.