Mating Disruption for Management of Oriental Fruit Moth in Stone and Pome Fruit
Table of Contents
Oriental fruit moth, Grapholita molesta (Busck), is a serious pest of stone fruit (peach, plum, apricot and occasionally cherry) and pome fruit (apples and pears) in most areas of Ontario. The oriental fruit moth (OFM) is a small (about 6-7 mm), greyish-brown moth with slightly silvery scales on its wings. A wavy pattern of light and dark scales is noticeable on newly emerged adult OFM. Moths are generally inconspicuous when their wings are folded (at rest).
Larvae feed on shoots or fruit depending on the crop and time of year. Newly hatched larvae are 1.5 mm long with a black head and white body; mature larvae are 9-13 mm in length with a brown head and pink body. There are 3 generations per year and sometimes a partial fourth generation. Other larvae similar in appearance that can infest stone and pome fruit are codling moth, plum curculio and European corn borer. It is therefore important to have larvae identified by a qualified entomologist/crop consultant.
Management of OFM is different in stone fruit and pome fruit orchards because of different harvest dates, variable development of the insect between crops, crop-specific pest complexes and established monitoring methods. However, the background information and basic procedures for mating disruption programs are similar for stone fruit and pome fruit. Hiring a qualified integrated pest management (IPM) consultant to help design and monitor a mating disruption program or any IPM program tailored to your specific situation is a wise investment.
Many species of insects, including OFM, communicate by using a variety of chemicals. Chemical signals that elicit a response from other members of the same species are called "pheromones". "Sex pheromones" attract one sex to the other so that mating can take place and are relatively common in the insect order Lepidoptera (moths and butterflies). Sex pheromones are a complex mixture of chemicals and each species has its own specific blend. In most species, it is the female moth that emits the sex pheromone and the male that follows the pheromone trail (or plume) to find the female.
Mating disruption (MD) technology uses synthetically produced pheromones to confuse males and limit their ability to locate "calling" females. If female moths do not mate, they cannot lay fertile eggs, and if their mating is delayed, they will lay fewer fertilized eggs in their lifetime. Consequently, the subsequent population is reduced, resulting in less crop damage.
When planning a MD program:
In peaches (and nectarines), OFM larvae feed on succulent shoots in the first generation, infest shoots and fruit during the second generation, and mainly attack fruit during subsequent generations. Thus, OFM is both an indirect and direct pest of peaches. Shoot damage is called "flagging" and is characterised by a drooping or "shepherd's crook" appearance of shoots (Figure 1). Frass (insect excrement) and entrance or exit holes are also usually obvious on infested shoots. In peaches, this damage can easily be seen from the ground, with no special training or equipment. OFM larvae readily move between peach shoots and a single larva damages 2-5 shoots during its development. Only one other pest (peach twig borer, Anarsia lineatella Zeller) causes similar damage but it is currently uncommon in Ontario. Peach canker and brown rot may infrequently cause somewhat similar shoot tip death, but it is easy to distinguish these problems on close examination, as no insect frass will be present. Monitoring for shoot damage early in the year is a good way to determine if control methods for OFM have been effective and to estimate the severity of the pest problem in an orchard from year to year.
Figure 1. "Flagging" or shoot damage on peach. Note entrance hole and frass (insect excrement) on underside of shoot.
Expanded acreage MD trials (18-48 ha blocks; 45-120 ac blocks) conducted in Ontario peach orchards showed that the technology is as effective as the use of insecticides in minimizing damage by OFM. Methods of applying pheromones for MD of OFM fall into 2 broad categories: hand-applied pheromone dispensers and sprayable pheromone formulations. A thorough discussion on both types of pheromone application technologies is contained in the OMAFRA Factsheet Mating Disruption for Management of Insect Pests, Order No. 03-079; review before choosing a MD product. A basic premise in using MD is that a minimum level of pheromone must be maintained in the orchard to prevent mating. Always follow the product label and do not reduce the recommended rate of pheromone dispensers or amount of sprayable pheromone used.
The 2 main forms of hand-applied dispensers are "twist-ties" (sometimes called "tube-type") and "clips" (or "ampoules"). There may be partial season dispensers (requiring more than 1 application per season or other strategy as outlined below) and season-long lasting dispensers of either type.
Apply twist-tie dispensers by twisting loosely around themselves (Figure 2) or coiling around a branch (Figure 3). Either way is acceptable as long as they stay on the tree and are not installed in such a way as to girdle branches. Clips are installed by simply snapping them onto branches of an appropriate size. For MD of OFM, apply dispensers at about 2 m from the ground or slightly higher. Do not put dispensers in exposed positions such as on dead limbs. From experience with MD products in Niagara peaches, it is clear that it is not absolutely critical to have dispensers in the top third of the trees for effective MD of OFM. However, some product labels indicate that dispensers do need to be in the top third of the trees. That recommendation should be followed for orchards or growers using MD for the first time and along orchard edges where possible.
Figure 2. "Twist-tie" type hand-applied pheromone dispenser twisted around itself.
Figure 3. "Twist-tie" dispenser coiled around branch.
Application time for hand-applied dispensers varies widely depending on the application rate of the particular dispenser (consult the product labels for appropriate rates). However, the largest factor determining speed of installation appears to be worker supervision. For twist-ties, workers should be able to cover 0.4-0.8 ha/hour (1-2 ac/hour) depending on application rate. Clip dispensers can be applied faster but do require the same care in branch choice. Dispensers should be put on sturdy branches (at least 1 cm in diameter) that are least likely to be pruned later. Worker education is also important to prevent dispensers from being cut out of peaches during normal spring pruning operations. If the same workers do both operations, prune-out is kept to a minimum.
Mating disruption programs usually rely on the application of pheromones before first flight of the target pest in the spring. First spring activity of any insect is highly dependent on weather conditions. Regional crop and pest reports are extremely helpful in determining the correct timing for any pest management decisions including the use of MD products.
Effective strategies verified in Ontario have been to:
Current OMAFRA recommendations include the use of insecticides directed at first generation larvae, whether or not MD is used, to ensure low pest pressure within the orchard. This is a conservative approach, and in areas where population pressure is low, where season-long area-wide mating disruption programs are being adopted, and where few alternative hosts are present, it may be possible to eventually discontinue insecticide applications for first generation OFM.
For season-long dispensers, timing of application in peaches is fairly straightforward. Season-long dispensers require only 1 application per year and provide approximately 120 days of effective activity. These products must be applied before OFM flight begins, ideally a few days to a week before expected first flight in the spring. In Niagara (in an average year), place season-long lasting dispensers in peach orchards around mid to late April.
For hand-applied pheromone MD products that do not last all season, there are 2 established options for a MD or partial MD program:
Sprayable pheromone products are available in Ontario for MD of several pests including OFM. The pheromone blends are encapsulated in microscopic polymer capsules and released slowly over time. Sprayable pheromones can be applied to orchards with standard spray equipment. Always check product labels for incompatibility notices. Extensive data has not been collected on compatibility of sprayable pheromones with other spray products, however field experience suggests that they are compatible with most commonly applied insecticides, miticides, and fungicides. It is preferable to apply sprayable pheromone formulations with a nozzle pressure at or below 150 psi, although higher pressures up to 250 psi have been tested and shown to have no detrimental effect on the formulation.
Sprayable pheromone formulations can be applied for any or all adult flights and should be applied to orchards as soon as the first moth is caught in pheromone traps in the spring or before first flight as indicated by regional monitoring and pest reports. Sprayable pheromone formulations have a shorter life span than hand-applied dispensers, although the registered sprayable OFM pheromone formulation (3M) will generally last for an entire adult flight period (5-6 weeks). Timing for re-application of sprayable pheromone products is important, since the product should be on the crop before first flight in the targeted generation. Where generations have prolonged emergence, multiple applications may be required.
Monitoring for OFM is conducted using pheromone-baited sticky traps. In a MD treated orchard, male moths should not be able to find pheromone-baited traps just as they are not able to locate female moths. However, a series of "sentinel" traps is recommended for MD treated orchards to ensure that the MD program is effective. Follow these points for using sentinel traps in MD orchards:
If no OFM are found in the traps, this is an indication that the MD program is working. A few OFM will usually be caught in border traps. This is not cause for alarm as the concentration of pheromones at MD block borders is sometimes lower than required for completely effective disruption. If more than 5 moths are found in a border trap from 1 monitoring date to the next, pay close attention to that border: look for flagging and fruit damage, and try to determine the source of infestation.
Consider a properly timed border application of insecticide only if the border trap catches are persistent or if monitoring indicates damage is occurring (see Shoot Damage Monitoring below). Base timing of such a supplemental spray, if necessary, on regional population monitoring. Discuss any border pesticide applications with a qualified crop consultant or provincial specialist.
In a Niagara demonstration project of MD of OFM in peaches (2000-2002, 25 orchards grouped into 5 blocks), very few orchards had border trap catches above 5 moths/monitoring day. Repeated sentinel trap catches above 5 moths were usually, but not always, correlated with slightly increased flagging and fruit damage in a very restricted area at the border. Since the damage was restricted to a small area, and was minor in nature, it was fairly clear in these cases that the cause of the problem was nearby sources of OFM, not an overall failure of MD in the orchards.
If you have been monitoring OFM populations using pheromone-baited sticky traps as part of your regular IPM program, you can no longer do so once you begin to use MD. In addition, trap catches are suppressed where hand-applied MD dispensers were used in the previous year, although the level of pheromone in this case is insufficient to prevent mating.
Sentinel traps indicate that MD is working. Identification of OFM damage to shoots is a direct measure of success. Shoot damage assessments are also recommended for insecticide-based management programs. Follow these steps for shoot damage assessments:
Peach shoot damage assessments are an important measure of MD efficacy. Monitoring as described above should take 2-3 hours for a 4 ha (10 ac) site assuming minimal shoot flagging. Make additional checks by walking around and through the MD block, looking for "hot spots" of flagging. However, do not substitute the rigorous assessments above with casual "walk-throughs" for damage assessments until you are very experienced with MD and monitoring, and only if the orchard has a verified, consistent history of low OFM damage. (Note: Remember that the damage thresholds used in MD blocks, as well as the monitoring techniques described herein, are also valid for conventional programs.)
Intervention with pesticides to minimize OFM damage is impossible once fruit damage has taken place. Once in the fruit, the larvae are protected against any sprays. However, it is helpful to record fruit damage by any pests and to have this information retained for future reference.
Record fruit damage monitoring separately for each peach variety if possible. Check 100-200 ripe fruit on the tree, not on the packing line. If any fruit have insect entrance or exit holes, cut the fruit open and identify any larvae. Alternatively, store the larvae in 70% alcohol and have a qualified IPM consultant identify them for you or send them to the Pest Diagnostic Clinic for identification.
OMAFRA Factsheet Mating Disruption for Management of Insect Pests, Order No. 03-079 contains a thorough review of the potential limitations of MD. Note that these limitations can be minimized or eliminated when MD is practiced over large areas; the larger the area, the more successful the MD program. In brief, those limitations include:
One additional limitation of MD, specifically for OFM in peaches, occurs when there are late season peaches or nectarines in areas where most fruit have been harvested. In these cases, the few late season fruit are the only targets left on which female moths can lay eggs. Pheromone products generally do not affect female moths and no MD product can prevent gravid (mated) females from flying into orchards from elsewhere. With large sites (co-operating neighbours) this is rarely a problem, but it does become an issue where a small MD site has late season fruit and all nearby conventional blocks have been harvested. In that situation, growers should apply a standard pre-pick spray to later varieties.
First generation OFM larvae will attack both apple shoots and developing fruitlets, causing both direct and indirect damage. Feeding activity of larvae in apple shoots does not result in the obvious flagging as observed in peach, and is easily overlooked without close examination of terminals. Oriental fruit moth "strikes" to apple shoots cause the terminals to appear somewhat desiccated, with limited drooping, and to eventually turn brown as the tissues die. Examination of affected shoots will often reveal a small entry hole, with frass (insect excrement) present (Figure 4). Larvae may enter through the side of the shoot, through the leaf petiole, or along the leaf mid-vein. Damage to shoots is primarily limited to that caused by first and second-generation larvae, while shoots are still relatively succulent. Some varieties (e.g. Mutsu) appear to be preferred over others and may be good early indicators of OFM activity in the orchard. Research indicates that OFM larvae typically infest a single apple shoot in completing their development.
Figure 4. Terminal shoot damage in apple. Note frass and ooze near entrance hole.
Figure 5. Early season OFM damage. Note entry through calyx.
Figure 6. OFM damage on apple. Note entry into fruit near calyx.
Fruit is attacked by all generations of OFM, with larvae entering through both the calyx and stem ends; in apple, larvae will often exit via the same hole through which they entered. Frass produced by the developing larvae is often evident on the fruit surface and infested fruit develop colour prematurely. However, late season damage can be difficult to detect, and infested apples may get through packing lines undetected.
Oriental fruit moth larvae are very similar in appearance to those of codling moth (CM). Both insects are white or cream coloured at egg hatch, developing a pink hue as the larvae mature. Of the two, CM is the larger insect; however, small larvae must be distinguished by examination of the last abdominal segment. Oriental fruit moth possess a small, dark, comb-like structure called an "anal comb" which can be seen using a good quality hand lens or, if the larvae are very small, using a microscope. It is critical that the pest is identified correctly, as the biology and management strategies of the two pests are different. Infested fruit should be collected and stored for examination by a qualified consultant or entomologist. Where the larva is no longer present, the fruit may be examined for the type of internal damage. Larval OFM generally tunnel inside the flesh of the fruit (Figure 7) avoiding the seeds, while codling moth larvae move directly into the seed cavity where they begin feeding on seeds (Figure 8).
Figure 7. Fruit infested with OFM. Note tunneling in flesh of apple.
Figure 8. Fruit infested with Codling moth. Note seed feeding.
OFM will also attack pears, usually entering fruit from mid season through to harvest. Pear shoots are rarely attacked. Due to the relatively late harvest dates of some pear varieties (September or early October) apply a MD program as described in the sections for apples.
For information on the types of MD products available, and instructions on how these products should be applied, see the general information, application techniques, and timing of application listed above in the peach sections Hand-applied Dispensers and Sprayable Pheromone Formulations.
There are several effective strategies for incorporating MD into an apple IPM program. Apples generally have a longer growing season than tender fruit. This may affect the choice of product(s) used and the timing of MD applications. Keep in mind that no single product provides true "season-long" management in apples, given the activity of the pest and the length of time the crop remains in the orchard. Take note of label recommendations for re-application.
Growers may choose to manage first generation OFM larvae with a registered insecticide, and apply MD for subsequent generations. Where this strategy is used, apply an insecticide for management of the first generation OFM with timing as directed by regional monitoring services. Alternatively, growers may opt for season-long management of OFM using MD. Where MD is used as part of a season-long management program, note that dispensers or pheromone sprays must be applied before first flight of the overwintering generation and will need re-application during the growing season.
Petal fall insecticide sprays directed at other apple pests may also suppress first generation OFM larvae. Consult the OMAFRA Publication 360, Fruit Production Recommendations for a listing of registered products recommended for managing OFM. Where OFM pressure is high, and/or organophosphate resistance to OFM is confirmed, MD programs should include the use of a supplemental insecticide directed at emerging first generation larvae (i.e. apply an insecticide in addition to the MD product - first generation only). In areas where population pressure is low, where season-long area-wide mating disruption programs are being adopted, and where few alternative hosts are present, it may be possible to eventually discontinue insecticide applications for first generation OFM. Effective strategies verified in Ontario to date have included the use of insecticides, with or without MD, to manage first generation OFM larvae.
A partial fourth generation may develop in some years, with adult activity into October. Even if an insecticide was used to manage the first generation larvae, followed by a longer-lived MD product for summer generations, re-application of a MD product or supplemental insecticide near harvest may be required to maintain protection in some years for late-season cultivars.
The use of pheromone traps for monitoring OFM is the same in apple (or pear) as it is in peaches. See Pheromone-baited Traps in the peach section of this Factsheet.
Sentinel traps (as described in Pheromone-baited traps in the peach section) provide a good indirect indication that MD is working; however, an important early measure of its success is the amount of terminal (shoot) damage in the orchard. Conduct terminal assessments for the 1st and 2nd generation OFM, approximately 2-3 weeks after peak flight. Examine a minimum of 50 terminals from 20 trees per 4 ha (10 ac) MD block, looking for signs of damage. No economic thresholds have been developed to correlate terminal damage in apples with fruit damage at harvest. However, if terminal damage is higher than 1-2%, this indicates your management strategy may not be providing adequate control of this pest. Based on the different number of shoots infested by a single larva in peach and apple, a 1-2% level of terminal strikes in apple represents a higher OFM population pressure than it would in peach.
After the larvae enter the fruit, they are protected from any sprays and intervention with insecticides is pointless. However, recording fruit damage from OFM can help identify weak areas of the MD program. Economic thresholds for OFM have not been developed for Ontario apple orchards; however, zero tolerance for infested fruit exists at the packing line. Unlike in peach orchards, OFM will attack apples early in the season, so conduct fruit damage assessments for each generation - this will provide an early indication of the management program's success. Conduct damage assessments approximately 2-3 weeks after peak flight of each generation. Examine a minimum of 50 fruit from 20 trees per 4 ha (10 ac) MD block, scanning carefully for any damage. Examine infested fruit for the presence of larvae; a qualified crop consultant should identify these. Levels of fruit damage higher than 1-2% indicate that the management strategy may not be providing adequate control of this pest, and a supplemental insecticide may be required for managing the subsequent generation(s). Discuss any required remedial action with a qualified consultant or provincial specialist.
Pheromones for MD are species specific and will not affect non-target species. OFM pheromone products will not affect other pests, such as codling moth or obliquebanded leafroller. Activity of other pests and beneficial insects and mites present in the orchard will also not be affected. Monitoring for other orchard pests should continue as usual.
The limitations of MD in apples are the same as those previously mentioned for peach, with a few additional comments.
The extended growing season, particularly in the production of late season varieties, requires that efficacy of the product be maintained well into October. Dispensers eventually run out pheromone and the output required to "confuse" the males is no longer maintained. If the MD dispensers are depleted before the end of the growing season, growers could see significant levels of late season damage.
Late-season monitoring is critical to managing this pest in apple; it is often a partial fourth generation of OFM from mid-September into October that causes the most significant crop loss in apples. The damage, often restricted to small entry holes at the calyx or stem end, is often not detected by picking crews or on the packing line. Plan ahead for your late season monitoring program and have personnel available to provide coverage until harvest is complete.
Oriental fruit moth is a cross-commodity pest, infesting both stone fruit and pome fruit. Growers with apples and peaches and/or other tree fruit may find adopting MD simplifies the management of this pest over their entire farm. Conventional IPM programs rely on insecticide applications timed to coincide with peak hatch of larvae, before they enter the fruit; MD targets the adults, limiting their ability to mate. As indicated previously, apples have a much longer growing season than peaches, with some late varieties being harvested in October. Leaving the crop in the orchard means that it is potentially vulnerable to attack by third and fourth generation OFM, if left unprotected. While MD may prevent mating in treated blocks, it does not control egg laying by immigrating mated females. Typically, damage is associated with border areas.
Growers choosing to apply MD to their apple blocks and insecticides to their peach blocks must consider the risk of late-season migration between crops. Using supplemental late-season insecticide sprays in apple blocks may provide some solutions, the timing of which would be based on trap counts obtained in adjacent peach blocks or from any available regional counts.
The cross-commodity nature of this pest provides a great case for co-operation between neighbouring growers, and for the adoption of area-wide MD programs in a given localized fruit production area.
Oriental fruit moth, an important pest of stone fruit and pome fruit in Ontario, can be effectively managed by using synthetic pheromones in mating disruption programs. Mating disruption (MD) programs require planning, monitoring and an understanding of this novel approach to pest management. Mating disruption programs require the treatment of an area, not a single variety or a few trees. Growers interested in using MD products should familiarize themselves with the OMAFRA Factsheets and infosheets on this topic including information on the OMAFRA web site.
There are important differences in MD products. Some hand-applied dispensers have season-long activity while others require more than one application per season. Sprayable formulations require accurate timing for re-application. In all cases, a regular monitoring program is a prerequisite for a successful MD program.
There are limitations to MD products, as there are for all pest management strategies. Successful demonstration projects and experimental use of MD in Ontario peach and apple orchards have shown that MD programs can be effective in managing OFM in commercial orchards. The adoption of community-based, area-wide MD programs will help to eliminate problems associated with emigration of mated females from unmanaged areas, and will address the management of the insect as a cross-commodity pest of stone fruit and pome fruit.
This Factsheet was reviewed by Grant Oliver, 3M Canada; Bernie Solymar, EarthTramper Consulting, Inc.; and Greg Stamm, CBC (America) Corp.
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