Managing Apple Maggot

As the summer quickly speeds by us, it is already time for monitoring for apple maggot in orchards in Ontario. Apple maggot adults begin emerging from pupae in the soil from June through until September, with peak flight occurring in August. Generally the male flies emerge earlier than the females. All newly emerged flies are sexually immature and must spend time feeding on honeydew excreted by other insects to acquire the protein needed to mature. Female flies lay their eggs individually, under the skin of the developing fruit. The larvae hatch within 3 to 7 days and begin burrowing into the fruit. After maturing, the larvae will leave the fruit and tunnel into the soil to pupate. These pupae can remain in the soil for up to 5 years if environmental conditions are not favourable for emergence. There is only one generation of apple maggot in Ontario each year.

Apple maggot larvae cause extensive damage to apples. The adult female lays her eggs in the fruit with her ovipositor, creating small stings or pin prick discolourations on the fruit which appear sunken or dimpled. The eggs hatch and the larvae begin tunneling within the fruit. These tunnels eventually begin to discolour, and are subsequently invaded by disease fungi such as Alternaria spp. and Pseudomonas spp. Heavily damaged apples are often aborted, however apples with only one or two stings will often remain on the tree until harvested.

Figure 1. Apple maggot stings on fruit

Figure 2. Larvae tunneling within fruit causes discolouration

Monitoring apple maggot populations is critical for timing spray applications to ensure effective control of this pest. In Ontario, we use five yellow sticky traps with lures (Figure 3) per site to monitor apple maggot. These traps should be placed in trees along the edge of the orchard. Place the boards on trees that are closest to an abandoned orchard or a stand of woods. If no abandoned trees or woodlands are nearby, use the southern edge of the block. Lures should be attached to the bottom of each of the sticky boards using a paperclip. Place the traps at least 30 feet from each other on the outside edge of the canopy at eye level. Make sure the traps are surrounded by leaves and fruit, but do not come in contact with them. Traps should be checked twice a week for apple maggot flies, which can be distinguished from other flies in the same species by the F banding on its wings.

Figure 3. Monitoring boards for apple maggots

Apple maggot is considered to be a quarantine pest and as a result there is zero tolerance for fruit infestation from this pest in Ontario. Insecticide sprays should be applied 7 to 10 days after the first female apple maggot fly is caught on a yellow board. Female apple maggots (Figure 4) can be distinguished from males since they are slightly larger and have a tapered abdomen, while males possess a rounded abdomen (Figure 5). Subsequent sprays should be applied every 14-21 days or as continued trap catches warrant. In orchards where trap catches are continuous and high, spray intervals should be shortened to 14 days. The timing of apple maggot sprays usually coincides with codling moth control applications, and as a result a single insecticide spray can often be used to manage both of these pests. It is important to remember that while some of the newer chemistries (Confirm, Assail) provide effective management of codling moth, they do not provide subsequent control of apple maggot. Currently organophophates are considered to be the most effective products registered for managing apple maggot. Research conducted by OMAFRA in Ontario (Hannah Fraser, 2002) has shown that Surround® WP Crop Protectant (kaolin clay) is an effective tool for managing apple maggot (along with many other orchard pests). Currently this product is only registered for sunburn control for apples in Canada, however, we are optimistic that this product will receive registration for managing apple maggot in the near future.

Figure 4. Female apple maggot fly - note tapered abdomen

Figure 5. Male apple maggot fly - note rounded abdomen