Oriental fruit moth (OFM)

Grapholita molesta

Written by: 

Jaime Pinero

Overview

Native to China, OFM is now found throughout much of the world. The adult OFM is approximately 1/4 inch (6.5mm) long and has a faint gray-brown salt-and-pepper pattern on its wings. Pupae are reddish brown. Fully developed larvae are about 1/2 inch (12.5mm) long, pink to white in color. Eggs are about 1/32 inch (0.7mm) in diameter, yellow-white, and laid singly on leaves or twigs.

Biology

OFM overwinters as a fully-grown larva (caterpillar), on limbs or trunk. First generation moths appear in May, and females lay their eggs on upper leaf surfaces, frequently on the terminal leaf of a young shoot. When the caterpillar hatches, it bores into the shoot, causing the terminal to wilt or “flag”. Later generations attack the fruit of both stone fruit and apples. In the northeastern United States, the OFM may have 3-5 generations (flights) per year, depending on weather conditions. As fruit develop the larvae will often enter near or through the stem end of stone fruit or calyx end of apple and bore directly into the interior of the fruit. OFM larvae do not feed on the seed; in contrast, codling moth larvae do feed on apple seeds.

Monitoring

Pheromone traps are available to monitor OFM activity and effectively time sprays. Traps are placed in the inside of the tree at eye level or higher just before bloom. Follow manufacturers’ guidelines for proper trap and lure maintenance and replacement. One trap per ten acres is recommended for commercial orchards, with a minimum of two traps.

Place sex pheromone traps in early April and check at least three times a week until biofix (i.e., first sustained capture of two or more moths per trap) is established. Then, calculate and record degree days to determine the percent egg hatch for each generation and timing of insecticide sprays (see ‘management’ below). Continue to monitor traps weekly throughout the season. Pheromone-baited OFM traps will also catch lesser apple worm, so it will be important to know how to distinguish between the two.

Trap threshold: In peaches, if there are >15 moths per trap per week for the first flight, there could be potential fruit infestation problems if control steps are not taken. The suggested trap threshold for OFM in peaches for 2nd - 4th  flight is 10 moths per trap per week. High trap counts do not trigger an immediate insecticide application; there is a lag period for egg hatch after the moths fly.

Management

Several management options are available for OMF including insecticide sprays and mating disruption. Regardless of the type of OFM management method chosen, careful monitoring is critical to the success of IPM tools.

Chemical control of the OFM can be improved by using a degree-day model to establish optimum timing of insecticide sprays targeting newly hatched larvae, since most insecticides are not effective at controlling adults. The most important spray against OFM on peaches is for the first generation. Keep in mind that there is a lag period for egg hatch after the moths fly. The first insecticide spray for OFM in peaches is recommended at 175 DD (base 45°F) after biofix. However, this often coincides with petal fall, so sprays targeting plum curculio should also control the 1st generation of OFM. Control measures for the second-generation egg hatch ought to occur at around 1,100 growing degree-days (base 45°F) after biofix.

With mating disruption, pheromone (sex attractant) dispensers are placed throughout the orchard. As the pheromone is released from the dispensers, male moths that normally use the pheromones to locate females become confused and fail to locate females. This interferes with the mating process. The densities of pheromone dispensers per acre depends on the formulation. Pheromone traps are used to evaluate the effectiveness of the mating disruption. If mating disruption is working, the pheromone traps should catch no moths. Mating disruption is only recommended for an orchard of 5 acres or larger in size.

If codling moth is also a problem in the same block, select a mating disruption material that releases pheromones of both species.