Oriental Fruit Moth

Adult oriental fruit moths are small, grayish moths about 0.4 inch long. These moths normally fly in the evenings just after sunset, or occasionally between daybreak and sunrise. Eggs are laid usually on the top of leaves and are disk-shaped, white to creamy in color when first laid, and about 0.03 inch in diameter. Just before hatching, the black head of the developing larva becomes visible. Larvae are white with a black head when first hatched. As they mature, they gradually turn pink with a brown head. Mature larvae are about 0.5 inch long. Use a hand lens to detect the presence of an anal comb under the last abdominal sclerite, which helps distinguish oriental fruit moth from other white or pink worms, such as codling moth, that may be found in stone fruits.

There are usually five generations per year in California, although a sixth generation has been observed in years with warm weather in early spring and late fall. Oriental fruit moths overwinter as mature, diapausing larvae inside tightly woven cocoons in protected places on the tree or in the trash near the base of the tree. In early spring, pupation takes place inside the cocoon and adults begin emerging in February or early March. Eggs are deposited on newly emerged shoots and the larva feed in terminals where they complete their development. Second-generation larvae feed in shoots, but fruit of some of the earlier-maturing nectarine cultivars may also be attacked. Subsequent generations may attack shoot terminals and green fruit, but as fruit matures it becomes the preferred site of attack by this pest.

Generally oriental fruit moth larvae bore deeper into the shoot than peach twig borer larvae do, and push granular frass out of the tunnel where it can often be seen. If the larvae are still present, cut strikes open and look for larvae to determine if the infestation is oriental fruit moth or peach twig borer.

Larvae damage developing shoots and fruit. Feeding on shoots kills the tip of the shoot, causing typical shoot strikes or flagging. However, the most severe damage occurs where larvae feed on fruit, causing it to be rated offgrade. Small larvae generally enter the fruit at the stem end, although entry can be made anywhere on the fruit, particularly where two fruits touch. Larvae immediately bore to the center of the fruit and feed around the pit. After reaching maturity, they exit from the fruit and pupate.

Use of mating disruptants is the preferred management strategy for oriental fruit moth. Alternatively, insecticide sprays timed according to degree-day accumulations can be used. There are many newly registered, less disruptive, and very effective insecticides that can be well integrated into an IPM Program. Careful monitoring is critical to the success of management tools.

The parasite Macrocentrus ancylivorus is a common parasite of oriental fruit moth larvae and peach twig borer larvae. In orchards when broad-spectrum insecticides are not used, parasitism can reach levels of 80 to 90% by August and September and help to provide long-term control of this pest.

Preliminary studies indicate that growing a small (0.3-0.5 acre) plot of sunflowers can provide Macrocentrus with an overwintering host, the sunflower moth Homoeosoma electellum, which allow its populations to build more rapidly in the orchard the following season. Planting sunflowers in a staggered planting in April and again in late May has proven to be a useful strategy.

Mating disruptant dispensers and sprays of the Entrust formulation of spinosad are organically acceptable; sprayable pheromones and puffers may not be accepted by certifiers.

Mating disruption orchards

Mating disruption is very effective for the first two generations and into the third generation. (Later generations are controlled, but not as consistently.) In most cases mating disruption can eliminate the need for insecticide sprays. To control oriental fruit moth by disrupting mating, put pheromone traps in the orchard by February 15 to detect the first moth emergence (see PHEROMONE TRAPS). As soon as moths have emerged, put out the mating disruption pheromone dispensers.

(In orchards where mating disruption was used the previous year, be sure to place new dispensers in the orchard no later than March 5. In some cases pheromone traps may fail to catch the first moth if dispensers from the previous year are still emitting pheromones.)

Depending on the duration of effectiveness for the dispensers, a second application of pheromone is needed in late July to early August for later-maturing varieties. (Sprayable pheromones may either be used for the first flight or substituted for the second application of pheromones dispensers.) In orchards with high populations of the parasite, Macrocentrus ancylivorus, a second application of pheromone dispensers may not even be necessary. This parasite, however, will not be abundant in orchards where a broad-spectrum insecticide has been used.

Pheromone-treated orchards must be carefully monitored for peach twig borer, oriental fruit moth, and other pests that can move in from neighboring stone fruit and almond orchards. Use pheromone traps as a backup to detect how well mating disruption is working. When no moths are caught in pheromone traps, it is a good indication that mating is being disrupted. However, also monitor shoot strikes to ensure the effectiveness of mating disruption.

Monitor shoot strikes (see SHOOT STRIKE MONITORING) in late April, mid-June, and mid-July, and sample fruit every week (with an emphasis on the final 4 weeks before harvest) see PREHARVEST FRUIT SAMPLES. If an orchard has more than an average of three shoot strikes per tree or if you find any larvae in the fruit, plan to treat the succeeding generation with an insecticide.

Conventional orchards

If you choose to manage oriental fruit moth with insecticides, use pheromone traps to monitor emergence of the second flight (late April to early May) to get a biofix. (Generally no insecticide treatment is applied to the first generation, except where populations are excessive, because of the erratic emergence and oviposition caused by variable weather conditions.) Use SHOOT STRIKE MONITORING and FRUIT MONITORING to determine need for treatment.

Put pheromone traps in the orchard by February 15 to detect when moth emerge for the first flight (see PHEROMONE TRAPS). Once the first moth is trapped, accumulate degree-days (DD) to estimate when the onset of the second flight will occur. Use a lower threshold of 45°F and an upper threshold of 90°F. The second flight should begin about 920 to 1,010 DD from the beginning of the initial flight; in some areas, however, the second flight may be seen as early as 800 DD.

Once the second flight has started, usually in May, accumulate degree-days. If a spray of methoxyfenozide (Intrepid) or chlorantraniliprole (Altacor) is planned, treat at 400 DD from the first trapped moth, otherwise, apply treatments from 500 to 600 DD. Treat at 400 to 500 DD for the third or fourth flight as fruit ripens.

Calculate degree-days for oriental fruit moth in nectarine for your location using the oriental fruit moth model or degree-day table. To learn more about using degree-days to time insecticide applications, watch the degree-days video.

Monitor moths until the crop is harvested in order to detect late-season peaks or migrations of moths from adjacent orchards. In orchards with heavy infestations, additional sprays will be needed to prevent fruit damage at harvest. Sprays must be carefully timed to kill newly hatched larvae before they bore into shoots or fruit. If treatments are needed for the third and fourth flights, spray at 400 to 500 DD after the start of the flight.

Also, monitor fruit for the presence of worms. Generally fruit is most heavily attacked in the tops of the trees, so fruit samples should be picked and examined from that area. Although green fruit can be attacked, fruit is most susceptible to attack by oriental fruit moth after color break. Treat if larvae are found in fruit.

All orchards

Examine fruit on trees every week after color break (see PREHARVEST FRUIT SAMPLES), to detect any developing problems in the orchard, and take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program, see FRUIT EVALUATION AT HARVEST. Record results (PDF) for harvest sample.

• Degree-day calculator
• Degree-day table
• Fruit sampling for pest damage in harvest (PDF)
• Using degree-days to time insecticide applications