How can I control cherry fruit fly?
Answer: The most serious insect pests of cherry are the cherry fruit fly and western cherry fruit fly (also known as black cherry fruit fly), Rhagoletis cingulata and R. fausta, respectively. For practical purposes, the two species can be considered together because life cycles and controls are essentially identical, though the western cherry fruit fly emerges from the soil 10 to 14 days earlier than the cherry fruit fly. In places like Michigan and New York, where both species overlap, there is a correspondingly longer period necessary to monitor and control.
Failure to adequately control these pests can cause severe crop loss due to the presence of fruit fly larvae (maggots) in the cherries at harvest. Both federal (USDA) regulations and consumers demand a zero tolerance for maggots in fruit at harvest, and this has forced growers into intensive spray-control programs to achieve perfect control. Commercial growers begin spraying when first fly emergence is detected on infested sentinel trees, or when temperature-driven phenology models indicate emergence has commenced in a given region.
This zero-tolerance policy also precludes many alternative methods of control for commercial growers. For instance, beneficial nematodes applied to the soil under cherry trees provided 80 to 88% control of fruit fly pupae in European trials), but the surviving pupae would become adults that could each lay 50 to 200 eggs. Though inadequate for commercial production, beneficial nematodes might provide sufficient control for the home grower.
Cherry fruit flies spend roughly 10 months of the year as pupae in the soil under the cherry trees, emerging as adults beginning in late May and continuing into July, depending on species and soil temperatures. Adults feed and mate but do not begin laying eggs for about 10 days; this period provides a window of opportunity for control. To monitor the emergence of the flies into the orchard, some sources suggest hanging yellow, sticky traps in the trees, but at least one source claims such traps can indicate emergence too late and that only temperature-driven phenology models can be trusted. Fortunately, in states with significant commercial cherry production, Cooperative Extension Service specialists offer such phenological data and provide pest-management alerts to growers. Contact your county Cooperative Extension Service to link to the cherry or cherry-pest-management specialists in your state.
After the 10-day feeding and mating period, flies begin to lay their eggs just under the skin of the fruit. Eggs hatch in five to seven days, and the maggots (larvae) feed on the pulp of the cherry. When fully grown, the larvae exit the fruit, drop to the ground, and begin their 10-month pupation in the soil.
Spinosad, derived from a naturally occurring bacteria, is quite effective at controlling the fruit fly, and it is approved for use as an organic pesticide in cherry production. It has been used in combination with bait, as well as applied as a foliar insecticide. The bait-plus-spinosad product (GF- 120NF) is an attractant that is lethal to flies that feed on it while “grazing” on the tree. This bait is “squirted” and spattered on the trees weekly at 20 fluid ounces per acre diluted in about 1.5 to two gallons of water per acre (it should NOT be applied with an air-blast sprayer). Entrust is a spinosad-based product that kills flies both by contact and residue, and, unlike GF-120NF, it can be applied with air-blast sprayer. Sprays of Entrust every seven to 10 days, beginning with fruit fly emergence (determined by trap catch), have provided excellent fruit fly control.
You can learn much more in the ATTRA publication Cherries: Organic Production. This publication focuses on organic pest and disease control and other topics relevant to organic production of both tart and sweet cherries. It introduces the Canadian bush cherry and discusses climatic considerations for cherry production. Information on marketing is included, as are further resources and sources of trees and pest-control materials.
Note: The mention of specific brand-name products is for educational purposes only and does not constitute endorsement by NCAT, ATTRA, or USDA.