In 2019, the last year the Rio Grande Valley produced a significant apple harvest, a severe case of apple maggot damage was found in two Corrales apple orchards. So what are apple maggots, and how are they different from codling moths? Codling moths lay eggs on the fruit and leaves of the tree. When the larvae hatches, they burrow into the core of the apple, leaving an entry point that is visible to the naked eye. Since most of the codling moth damage occurs at the apple core, minor codling moth damage may be removed so the rest of the fruit is edible.
Apple maggot flies are a tiny quarter-inch fly that lays its eggs by piercing the skin of the apple. Each female apple maggot fly can lay hundreds of eggs. Each point where the apple is pierced leaves a small dent with a tiny dot in the middle where an egg was laid. When the eggs hatch, the larvae wind their way through the fruit leaving a trail of frass. Because of the number of times the fruit is pierced, the fruit becomes inedible. Both codling moth larvae and apple maggot larvae overwinter in the soil in a pupa state.
Steve Lucero, of the Sandoval County Cooperative Extension Service suggests these treatment options. Codling moths appear in late May. The moths are approximately half-inch long with grey and brown bands and they appear at dawn and dusk. Upon appearance, begin applying a pesticide such as an organically approved spinosad or kaolin clay. Spray the trees every two weeks from mid-June until the end of August.
Unlike the codling moth, only one generation of apple maggot flies is produced each year. Apple maggots appear starting in June and continue through most of the summer. Adult flies often leave and feed outside the orchard, in wooded or brushy areas. There is no cure for apple maggots once they are inside the apples. Controls must prevent damage by stopping the flies before they lay their eggs. To monitor for apple maggots, hang sticky traps from the tree at eye level in early summer and replace them every three to four weeks. Treatment options are in links below.
The insecticides recommended in this article are effective but they do have negative impacts on pollinators. NMSU recommends weeding/mowing flowering plants in the orchard that might be contaminated with drift and not to spray when it is windy to reduce drift. See https://extension.umn.edu/yard-and-garden-insects/apple-maggot; and https://extension.usu.edu/pests/ipm/notes_ag/fruit-apple-maggot