Cherry fruit fly ecology and management
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Although there are three potential picture-winged flies that attack cherries in Michigan, the cherry fruit fly is the main culprit in most areas of the state. This species has been found in cultivated tart and sweet cherries as well as in the wild host – wild black cherry. Black cherry fruit flies also show up as pests in managed blocks of tart and sweet cherry, especially in southwest Michigan. In the wild, they are found predominantly in pin cherry. From a control standpoint, these two species of fruit fly are often considered one pest and managed identically. Cherry fruit flies are a key pest of cherry orchards, as they cause damage to the fruit by adult and larval feeding as well as by adult oviposition. However, the biggest concern for growers is the larvae that develop within the fruit. The cherry industry has a “zero tolerance” policy for larvae in the fruit at harvest. Therefore, successful cherry fruit fly control is vital.
Cherry fruit fly adults emerge from overwintering puparia over a period of 6 to 8 weeks beginning in early June. In recent years, monitoring of cherry fruit fly populations by IPM practitioners has indicated that the highest fly captures in some managed orchards occur after harvest. In response to these reports, in 2005 we initiated a study seeking to establish the phenology of cherry fruit fly, using traps to capture adult flies and fruit sampling to determine larval infestation. We found three major flight periods in the sites we monitored: an early flight peaking prior to harvest in unmanaged orchards, an extended midseason flight peaking after harvest in managed orchards, and a late flight in natural habitats (black cherry trees).
There was general agreement with respect to the timing of cherry fruit fly activity between fly captures on traps and larval infestation of fruit. Infestation was already high in late June in the unmanaged orchards and increased until mid-July, immediately before fruit began deteriorating and dropping from the trees. In contrast, infestation in managed orchards was relatively low in late June and early July, before harvest. At these sites, infestation increased after harvest, in late July or early August. In the natural site, infestation started in early August and increased through the month. Regarding the major concern of cherry growers, which is the presence of flies in managed orchards in the period immediately before harvest, our data indicated the presence of resident cherry fruit fly populations in the managed orchards we monitored. At these sites, flies captured before harvest represent the early part of a flight curve peaking immediately post harvest, rather than populations outside of the orchard as has been generally assumed.
Once flies emerge, they spend 10 days feeding on plant juices, dew or from the surface of the leaves or fruit. This post-emergence feeding is called the pre-oviposition period where adults feed and mate. This period of time offers growers an advantage for a control strategy – they can apply insecticide to kill adult flies before they lay eggs. Traditionally cherry fruit fly control has been based on the “first fly caught.” After this first emergence, there is a 7 to 10 day time frame in which growers apply insecticide.
Monitoring protocols for adult cherry fruit fly activity have improved in recent years. Traps can be a valuable management tools as they provide a relative estimate of pest pressure and an indication as to when control measures should begin. Adult emergence and seasonal activity is best monitored using attractant-baited yellow sticky traps. Good protocols include placing traps in perimeter rows, baiting with an ammonia source and checking the traps at least weekly and more frequently at the start of emergence. Placement of the traps within the canopy is also important: traps should be placed as high in the canopy as possible. Indeed, studies conducted in Michigan have revealed that very few flies are captured when traps are placed low in the canopy. The highest captures, by far, were recorded in the upper part of the canopy. We are currently investigating the benefits of monitoring cherry fruit fly in the upper canopy by placing traps on a PVC or bamboo pole, and will update the industry on our findings this winter.
Control options include insecticides in the organophosphate (OP) class, synthetic pyrethroids, and more recently the neonicotinoids, Fruit Fly Baited insecticides and Particle Film. The OP’s, like Guthion and Imidan, have been the standard for control because of their contact activity on cherry fruit fly and long stable residues. The synthetic pyrethroids, like Asana and Warrior, also have contact poisons activity on cherry fruit fly adults but generally provide only moderate control because of short residual activity. Two new control options on the market are the neonicotinoids Provado and Actara, which have performed well in field efficacy trials. Provado has a 7-day pre-harvest interval, while the PHI for Actara is 14 days. Thus, Provado provides a good option for cherry fruit fly control at that critical window of a week or so before harvest. Additionally, it is registered for use in both sweets and tarts. Since Actara is also active on plum curculio, economical options for using this material would be a single application at 4.5 to 5.5 ounces/acre at second cover or a few weeks before harvest when control of both pests is often needed. Organic cherry growers may want to consider use of GF120 Fruit Fly Bait, Entrust (organic formulation of SpinTor) or Surround WP (kaolin). GF120 Fruit Fly Bait has been shown to provide effective control on various fruit fly species, but requires precise timing (cherry fruit fly pre-oviposition period) and specialized application equipment. Entrust has shown to be active on fruit fly species but starting sprays during the pre-oviposition period on a 7 day interval is important for good performance. Field trials with Surround WP have shown good fruit protection from cherry fruit fly when used on large blocks when coverage is maintained.
As a final management note, having fly populations infesting fruit that remain on the tree after harvest may be problematic because resident populations represent a source of infestation the following year. Growers with known high fly captures or fruit infestation post-harvest should consider applying an insecticide at this time to combat the resident populations and maintain them at such a low level that the threat of infestation prior to harvest is negligible. Our initial work on post-harvest cherry fruit fly treatments has indicated that the critical time to apply an insecticide is within the first week after harvest.
Dr. Gut’s work is funded in part by MSU‘s AgBioResearch.