Apple Maggot Control: Effective Strategies to Protect Apple Trees and Healthy Fruit

I have learned that the apple maggot, Rhagoletis pomonella, is a pest that will inflict some damage on apples if I'm using them commercially, so I ought to get a handle on it before the damage actually shows up. The adult fly deposits the eggs under the apple fruit and the resulting larvae bore through the fruit causing internal rot as well as feeding externally creating brown lines in the apple. Monitoring apple fly is the key to successful apple maggot control (after the larvae develop inside the fruit), and dealing with adults at the right time. 

In commercial orchards I would control this pest using integrated pest management (IPM), in addition to orchard sanitation practices I would incorporate traps into the plan and regular scouting and treatments as needed and timing to prevent and delay applications on a fixed schedule.

How can you tell if there is apple maggot damage?

Fruit inspection is the first step I take and I check for apple maggot damage. The eggs are laid singly by adult females, under the skin of the apple. Larvae develop inside the flesh after hatching leaving tunnels in the flesh that are brown or discolored. The fruit will react to this injury and microorganisms that accompany the maggots may be responsible for discoloration and rot within the fruit itself. 

Damage may not be apparent initially. However, the flesh colour discolours and softens as feeding goes on and heavily infested apples may be distorted and unsuitable for fresh market sales. Heavily infested fruit may develop misshapen and become inedible, says Minnesota Extension. 

This is why I don't wait for fruit damage that I can see before beginning to execute my program of action. When I slice the apple open and see many tunnels, it's because the pest has completed the most susceptible stage, at least here in the U.S. Apples first become infested only in late July or August.Here in the U.S., apples are first infested only in late July or August and by the time I slice an apple apart to find many tunnels, it has selected the most susceptible time.

Researchers need to understand how the apple maggot fly develops

The apple maggot fly life cycle knowledge enables me to be aware of the time when this pest is vulnerable. The early life stages of the insect are hidden within or near fruit and soil; however, the adult fly is the significant exposed stage to be monitored in the orchard and treated.

The mature larvae emerge from infested apples after they have fallen on the ground, and pupate in the ground. The adults fly out the next summer. One generation is produced annually in Pennsylvania with a small percentage in soil for two or more years. 

Emergence of adults varies according to region and weather. The emergence can take place between late June and early July into summer, with activity maximum during the latter portion of July and early August as reported by Minnesota Extension. 

Adults emerge and will feed and mature before females will lay eggs. Normally, females will produce hundreds of eggs in their about-30-day adult life, casting them singly under the skin of the apple.

A grower perspective opens up an important management window whereby adult flies are monitored and controlled before their eggs lay and larvae develop within the fruit.

What will increase apple maggot pressure?

How to prevent apple maggots? I do not only pay attention to what is going around my orchard but also what is outside of the commercial block. Unmanaged host plants and abandoned apple trees can continue to maintain apples containing apple maggot concentrations similar to productive apple trees. The management of abandoned apple trees and alternate hosts in or close to orchards may hinder orchard sanitation; thus, Penn State suggests that these should be removed where possible. 

The falling apples are another problem. Once an apple affected with infestation has fallen to the ground, mature larvae may detach and go to the ground to pupate. Therefore, the frequency of the fruit being picked up will have a beneficial effect on reducing re-entry of larvae into the soil, but will not be sufficient control if neighboring unmanaged hosts are present. 

Risk may also be affected by the characteristics of the cultivar. Apple varieties with early maturity dates and peel too thin are more vulnerable to infestation, Penn State notes. This means that I need to be extra careful on susceptible blocks and not just outright using the same treatment on all of the blocks.

What are the acceptable ways for farmers to check when to spray apple maggot?

One of those most useful aspects of an apple maggot control program for me, is that if the adults are trapped it means that they exist. Rather than following the calendar to spray, I can consider trap catch data to decide whether or not to spray.

The red sticky spheres are specifically valuable as the coloration of the sphere looks very similar to fruit and are effective with a volatile attractant that is related to the apple. Penn State advises installing trapping red sticky spheres in orchard blocks and monitoring them frequently. Its PA guidance is based on an average of five flies per trap. 

Adult emergence can be detected by using yellow sticky traps, and the red sphere traps can be effective in monitoring flies responding to the visual and odour of apples.

The typical monitoring plan is as follows:

There are no universally agreed upon trap thresholds. So, for me I'd take the threshold suggested by my local extension service and act on the pesticide instructions displayed on the label that would apply in my orchard.

When to Spray for Apple Maggots?

When to spray apple maggots depends closely on adult emergence and captures in traps. Control of the "less exposed adult fly" before the female lays eggs, not preventing damage from larvae once eggs have been set.

Penn State advises applying insecticide if the insect trap thresholds are surpassed and cautions special focus on adult insects before they lay eggs. The number of flies per red sticky sphere used to determine when to treat is 5, on average, in Pennsylvania. Other monitoring systems, thresholds or treatment schedules can be used elsewhere. This is why I would not follow any single national spray schedule. The treatment window can be affected by temperature, adult emergence, orchard history, and the number of adults collected in the trap and pest management recommendations.

The timing of commercial Apple Maggot treatment is dependent on the timing of the flight period.

Recommending the best insecticide to control apple maggot

No single organism in a commercial apple orchard will excel in control of apple maggot. Resistance-management needs and application considerations differ among regions, as do product registrations and local regulations.

The second, more important concept is that where and when the product acts. The back end-feeding behavior of the larvae doesn't scout; I want my treatment to be before the egg deposit. As did IPM, an emphasis was placed on targeting the emerging adult flies and that not all orchards need to be treated. 

Apple maggot programs may apply baited treatments and insecticides like spinosad and pyrethroids or registered alternatives depending on geographical registration. Penn State, for example, offers multiple groups of insecticides to control apple maggot, with emphasis on timing to take advantage of traps for commercial use. 

I would also consider rotating products with different modes of action when repeated applications are needed as well as other methods of resistance management when relying on the same chemistry. Apple maggot treatment should include protection of pollinators, spray interval, pre harvest interval, all other label restrictions etc. In the upcoming sections, we shall discuss the best insecticide for apple maggot.

So, what can be used by farmers for apple maggot organic control?

Prevention and monitoring continue to play a major role with apple maggot organic control. Better organic production does not imply the loss of the need to consider timing of treatments. Indeed, good scouting and sanitation can be even more valuable when the number of allowable products is reduced.

Mass trapping may be beneficial. Dark-colored sticky spheres have been shown to minimize damage by apple maggots by organic growers in the eastern United States, according to UC IPM. Some fermented baited sprays, (such as GF-120), are also included as organically acceptable practices if approved. 

An organic program for a commercial grower can thus result in the combination of:

• Regular trap monitoring
• Fruit that drops from the tree needs to be removed.
• Abandoned host trees should be a major part of the management approach.
• Using mass trapping as appropriate
• Approved baited sprays
• Proper orchard sanitation
• Pest pressure and adult emergence reported and recorded with care.

The product such as organic pesticide for apple maggot and method should always be checked for compliance against organic current requirements and current product registration for intended crop and pest.

Is Beauveria bassiana feasible for biological control of apple maggot?

Beauveria bassiana is an entomopathogenic fungus that can be employed in biological insect management. Its spores adhere to the insect's cuticle, germinate and invade the exterior of the insect. The fungus then grows inside the insect, and it may cause its death. Novobac 's insecticidal products have this labeled mode of action for apple maggot organic control. 

But one note is important when talking about B. bassiana specifically for the apple maggot. The larvae of the pest are protected within the apple during feeding and have made that the favorable period for them. For this reason, biological control agents are not highly effective against apple maggot, notes UC IPM. 

I don't consider B. bassiana to be a "silver bullet" for established apple maggot treatment. If a locally-registered product specifically allows for use to reduce the pest level, a microbial insecticide may be considered as a part of a larger IPM plan, targeting the available pest stage.

What role can Beveria WP play in an Apple Maggot IPM Program?

Beveria WP, for apple maggot organic control, is a bio-insecticide which contains the active ingredient Beauveria bassiana. According to Novobac's product Information it is a Wettable-Powder formulation of B. bassiana and targets the following insects: whitefly, thrips, aphids, psyllids, mealybugs, beetles, plant bugs and weevils. The documented mode of action is contact: fungal spore adhering to susceptible insect, germinating and penetrating the insect cuticle and then developing inside the host insect.

But an essential point for me is different for apple maggot control. Beveria WP was not registered for field use against apple maggot by Novobac. It should no longer be recommended on the grounds that it is an effective treatment for apple maggots or approved for that purpose unless the product label and local registration specifically allows.

This is relevant when it comes to commercial agriculture. A biological product may have value as part of an IPM program, but it shouldn't be added because the active ingredient is known to be insecticidal but not necessarily effective against the specific registered target pest and allowable crop use.

A season long orchard program for apple maggot control

How to prevent apple maggots? The decision to spray or not to spray apple maggots for prevention is one that is made for the entire season.

Prior to the growing season I would pull for visits around commercial blocks to find abandoned apple trees and unmanaged host sources. I would set up monitoring traps in early summer prior to expected adult emergence. Begin trapping as soon as flies are seen in the orchard and record the number of flies captured on a per orchard block basis.

In such a case, were I to collect the recommended level of captures, I would aim at the adult flies with a treatment registered locally with an appropriate dose. Post treatment monitoring is necessary as the adults may emerge over a number of weeks.

If possible, removing drop and damaged fruit at harvest will minimize the amount of mature larvae in the soil. Once harvested, I would sight check the traps, see what apple maggot damage had occurred and check the treatment dates to look for high pressure blocks to be used in the next season's IPM program. 

The main concept is the simple one of interrupting the apple maggot fly life cycle before the larvae enter the apple.

So What do Commercial Farmers Need to Remember on Apple Maggot Control?

How to prevent apple maggots? The first step in effective control of the apple maggot is to catch the adult fly in the early stages. The maggot visible inside an apple is proof that the pest has gone through the most available stage of development.

Monitoring, sanitation, trapping and the timely applications of adult control should therefore be properly integrated in a commercial program. Apple maggot organic control of unmanaged host sources mechanically reduces pressure and traps can be used to determine when adult pressure has begun. These treatments should then be chosen and timed following local recommendations, product registrations and orchard conditions.

Organic/biological tools can be part of an IPM program as well, but should not be considered interchangeable. Protected feeding by apple maggot larvae does not make biological control of larvae in fruit very useful, and Beauveria bassiana has biological insecticidal activity. 

Because there is no documentation to support the potential apple maggot effectivity on a commercial scale, the safest strategy with products like Beveria WP is to list the target pests on the label and follow the label as written. 

The commercial grower's approach may simply be based on keeping an eye on the adult fly, avoiding the egg-laying period and controlling the orchard sources before infestation is discovered in damaged apples.

References:

1. Świergiel, Weronika, et al. “Soil application of Beauveria bassiana GHA against apple sawfly, Hoplocampa testudinea (Hymenoptera: Tenthredinidae): Field mortality and fungal persistence.” Insect Science 23.6 (2016): 854-868.
2. Cossentine, J. E., et al. “Susceptibility of apple clearwing moth larvae, Synanthedon myopaeformis (Lepidoptera: Sesiidae) to Beauveria bassiana and Metarhizium brunneum.” Biocontrol Science and Technology 20.7 (2010): 703-707.