How can I control Oriental fruit moth in peaches?
Answer: The Oriental fruit moth (Grapholitha molesta) is related to the codling moth, a pest of apples, and causes the same type of fruit damage. Larvae burrow in the new shoots in the spring, then move through the stem into the developing fruit. They feed near the pit, so there may be no visible damage to the fruit on the surface, but the fruits become much more susceptible to brown rot, and they break down rapidly after harvest.
There are up to seven generations of worms each year, with the earliest one feeding on young leafy shoots in the same way the peach twig borer does, and later generations feeding on the fruit, like the codling moth in apples. The overwintering stage is a full-grown larva from the last generation of the previous season. The larva spins a cocoon in the litter around the trees or on the bark itself. Pupation and adult emergence occur in the spring, and the moths lay their first eggs just after the peaches bloom. Trees that are allowed to grow dense, succulent foliage are especially attractive to the moths.
Pheromone-based mating disruption systems for Oriental fruit moth are proven, effective, and easy to use. One product, the Isomate-M™ pheromone dispenser, has proven as effective as chemical control in California tests. There are some restrictions to pheromone use in organic production, concerning inert ingredients, so organic growers should check the regulations before purchasing a particular system.
Degree-day models or charts can help growers in timing pesticide application or placing mating disruption lures to coincide with the emergence of the pest. Many state Extension offices or universities provide timing tools developed specifically for their regions.
In addition to pheromonal mating disruption, control measures could include planting the right peach varieties. Early-maturing types discourage damage because the peaches are picked before the insects attack the fruit. This reduction in the moths’ food supply helps control their population. Remove infested fruit and stem tips to further reduce populations. Good orchard sanitation —removing leaf litter and dropped or culled fruit where larvae overwinter — will further reduce attacks. Dormant larvae can be destroyed by cultivating to a depth of two to four inches, one to three weeks before the peaches bloom. Another part of cultural control is annual pruning to control overly vigorous growth on the trees, making them less attractive to the moths. Parasitic braconid wasps can be used as part of an IPM strategy against the Oriental fruit moth. Growers have had success with five releases of adult wasps four days apart, beginning in May and using about 500 adults per acre. To control the moth effectively, some growers supplement a parasitic insect program with a single spray of an appropriate insecticide shortly before harvest.
One of these braconid wasps, Macrocentrus ancylivorus, is being researched by the University of California’s Walter Bentley (Kearney Agriculture Center). He observed that while the wasp was effective, it could not successfully overwinter on the fruit moth. Bentley planted about ¼ acre of sunflowers in three consecutive plantings (May, June, July) adjacent to his 3-acre research plot of peaches. The sunflower is a host for the sunflower moth (Homeosoma electellum), which itself is a good overwintering host for the wasp. This strategy led to a high rate of parasitism of the Oriental fruit moth and allowed the wasp to overwinter successfully on the sunflower moth. The result is that orchard managers might not in the future have to buy and release these parasitoids repeatedly.
You’ll benefit from reading the ATTRA publication Peaches: Organic and Low-Spray Production. It describes the major diseases and insect pests of peaches and discusses organic or least-toxic control options for each. It emphasizes the considerable climatic differences between the arid West, which is relatively amenable to organic peach production, and the humid East, where it is more difficult to grow peaches without synthetic fungicides and insecticides. While you’re on our website, also check out ATTRA Identification Sheet: Peach Insect Pests, which serves as a handy guide to help identify pests and learn about solutions.