We wanted to test the effectiveness of combining a visual trap/odor bait with a commercially available, organically approved GF-120 insecticide/bait for controlling apple maggot fly in New England apple orchards. We positioned traps that were dipped in the GF-120 at 5 meter intervals around the perimeter of the orchard, and compared that with another block with “sticky” traps (covered with Tangletrap) around the perimeter plus GF-120 applied to the foliage throughout the block, and a third block with the GF-120 applied to foliage with no border traps. Non-baited monitoring traps were placed in the center of each block, and the traps were checked weekly, as well as weekly visual inspection of fruit for signs of apple maggot fly egglaying or larval tunneling. The project began in late June and was completed in late September 2017. There was no apple maggot injury in any of the three test blocks, and the monitoring traps in the center of the orchard had very few captures. This result was encouraging, but we regard it with caution because of a relatively low population of apple maggot flies moving into the orchard this season from wild trees, compared to other years. In addition, we believe that the need for repeated applications of the GF-120 after rainfall would make this method unacceptably expensive in money and time. We would like to explore possibilities for extending the longevity of the material in the field, perhaps by placing a clear plastic dome above the trap. Outreach is ongoing, with presentations at grower meetings (upcoming) and research meetings, several mentions in Polaris Orchard Management’s “Weekly Worrier” newsletter, and consultations with interested Polaris Orchard Management clients.
Apple maggot fly is an important pest in Northeast apple orchards annually from mid-summer through early fall. Growers are confronted with a challenge in attempting to control this pest: on the one hand, consumer, retailer, and exporter tolerance for apple maggot fly injury is virtually zero, not only because of aesthetics, but because larval tunneling in fruit can rapidly degrade fruit quality. On the other hand, only a few available pesticides provide adequate control of this insect, most of which are under scrutiny by regulators or (mainly) retail buyers. Organic growers have even fewer effective control options. A long-standing goal of growers and researchers in this region has been the use of odor-baited red sphere traps to intercept flies immigrating into orchards, which has been shown to be a highly effective tactic, but the logistical barriers to using the sticky-coated traps are almost insurmountable. Replacing the sticky with a pesticide and bait impregnated cap is a method which has been in development for many years but is still unavailable commercially. Meanwhile, West Coast growers use a toxicant bait formula (which is also approved for organic use) for controlling a related species, cherry fruit fly; East Coast trials have shown some effectiveness of this material on apple maggot. We propose replacing the current insecticide-bait cap with a coating of this toxicant bait (GF-120) on red sphere traps as a potential method of controlling apple maggot fly with virtually no pesticide in the environment.
Replacing broad-spectrum insecticides with behaviorally based methods for apple maggot control
has a long-standing goal of IPM researchers, growers, and consultants in the northeast U.S. for
several decades. Combining two tactics that have separately been found to be successful – using
odor-baited sphere traps to intercept immigrating flies, and using the toxicant bait developed on the
west coast for cherry fruit fly control – could bring us a step closer to realizing this goal. Both
organic and IPM growers would potentially benefit from controlling a key pest with minimal, highly
targeted, insecticide use.
Objective 1: Test the effectiveness of GF-120 applied directly to baited red sphere traps as a
replacement for sticky coating or pesticide-bait impregnated trap caps.
Objective 2: Compare the effectiveness of border trapping with GF-120 with the application of the
material to fruit and foliage, with and without baited sticky traps in border trees.
Objective 3: Communicate the results of this work to growers and others in the northeast via
newsletters, orchard tours, and publications.
Red sphere traps baited with synthetic apple odor and coated with GF-120 insecticide bait were be set out on the perimeter of the block at about 5 meter intervals. Sticky-coated baited red spheres were be set out similarly on the border of an adjacent block and also receive GF-120 applied to the foliage with a backpack sprayer, and a third block received the backpack application of GF-120 with no border sphere traps. The traps were set out in late June and monitored weekly through mid-September. GF-120 was refreshed as needed on traps and/or foliage according to rainfall (> 2″) or time (> 10 days). Red sphere traps with no apple odor or bait were set out in the center of the block to determine if flies are moving into the block in spite of the treatment. Fruit were also monitored for the appearance of apple maggot fly egg-laying and larval tunneling throughout this time.
There was no apple maggot egg-laying or larval tunneling injury in any test block from 30 June, when the traps were set out, through harvest in late September. The unbaited traps in block interiors never reached threshold in any test block; the peak capture was 2 flies on 4 traps on 1 July, with zero captures on all traps in most weeks. However, population pressure from apple maggot fly was relatively low this year (perhaps owing to lack of fruit in 2016?), and examining the border sticky traps confirmed that numbers were low, averaging less than one per trap per week over the course of the season. Thus it is not clear that this technique would work for higher populations.
Because of the incessant rains through the summer and into early fall, keeping up with re-application of GF-120 was a constant challenge, both the direct application to the traps (which needed to be done weekly), and the backpack pump sprayer application to the foliage (which needed to be done every ten days). Twenty-eight traps ringing a 1.5 acre block required about 6-8 ounces of GF-120 each week, taking about 20 minutes, and the backpack sprayer required a similar input of time and material. The material cost of GF-120 works out to about $70 per acre over the course of the season.
We hoped to provide acceptable control of apple maggot fly using the baited traps, and we are cautiously optimistic about the effectiveness of the method, which seems to have performed well at least under modest apple maggot fly pressure. However, the lack of retention of the material, noted by others who have tried using GF-120 in the Northeast, was even worse than anticipated, requiring weekly re-application to achieve an effective amount of material on the trap. Using some sort of ‘umbrella’ similar to the plastic domes used in Utah for cherry maggot fly might help, although it is important not to interfere with the fly’s visual perception of the trap. A colleague suggested that an inverted clear plastic dish could be suspended a few inches over the trap to help keep most of the rain off, and we think this would definitely be worth a try! It would be more difficult to improve the longevity of the foliar application, unless some sort of ‘sticker’ adjuvant could be used to keep in on the leaf for longer, without interfering with the effectiveness or attractiveness of the material to the flies.
Education & Outreach Activities and Participation Summary
The results of the project were described several times in Polaris Orchard Management’s “Weekly Worrier” newsletter, which reaches 30+ growers in the region, as well as 10+ Extension workers, other consultants, and industry representatives. A presentation (.pdf above) was given at the annual New York, New England, Canadian Fruit Pest Management Workshop in Burlington, VT. In February, a poster presentation will be offered at the Vermont NOFA Winter Meeting in Burlington VT, and information will be provided to consultant colleagues in March at the Northeast Crop Consultants’ Conference in Cananaigua, NY. We will also make an effort to coordinate with UMass Extension to have a grower meeting at Clark Brothers Orchard in early summer so that we can describe the project and ongoing work.
Using new techniques for controlling apple maggot fly
We were very pleased to have good control of apple maggot, regardless of the reason! This insect has been a challenge for Clark Brothers with the EcoApple label — high populations plus mediocre material efficacy have caused damage in the past. At this farm particularly, with the high level of hail injury that was already impacting the crop, it was great not to have to worry about another source of damage at harvest, and to be able to keep well within the guidelines for ecological practices.
It was the best of years, and the worst of years — the low population of apple maggot flies on the one hand, and the absolutely ridiculous amount of rainfall on the other! As already mentioned, we’d like to look into ways to retain the material on the trap so that it can go on working. Also, we launched into field trials before having information on the behavioral response of the flies to the GF-120 traps, which it would be good to go back and learn more about. Another potential improvement would be reducing the number of traps needed — Dr. Ronald Prokopy at one point had developed a formula for determining how widely spaced the traps can be depending on habitat, variety, tree size and pruning regimen. For this trial, we used the most conservative spacing, but in future work, it may be possible to reduce the number of traps by as much as half.
Eco-label and organic growers could potentially benefit the most from this work, but many commercial growers might also find it helpful. Insecticides that are used in the summer for lepidopteran pests like obliquebanded leafroller tend to have good but not excellent effectiveness on apple maggot fly, so a boost in control offered by the traps could be very beneficial… IF we can reduce the time and material needed!
Several Extension researchers we have spoken to seem interested in these results, so we are hopeful that some good collaborations could result from this work.