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Funded Project |
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Funding Program:
Regional IPM Competitive Grants - Northeastern |
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Project Title:
Bio-Based Methods of Reducing Insecticide Use Against Two Key Apple Pests |
Project Directors (PDs):
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Lead State: MA Lead Organization: University of Massachusetts |
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Cooperating State(s):
Maine |
| Research Funding: $100,000 |
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Start Date: Sep-01-1999 End Date: Aug-31-2002 |
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Pests Involved: apple maggots, plum curculios |
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Site/Commodity: apples |
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Area of Emphasis: biological control, biocontrol |
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Summary:
Apples are among the most valuable and widely grown crops in the Northeast, worth about 400 million dollars annually. The apple maggot and the plum curculio, both native to the Northeast, are key pests of apples, each damaging a great majority of fruit on unmanaged trees. In recent surveys, northeast orchardists ranked plum curculio first and apple maggot second in importance among arthropod pests attacking apple trees. Because as yet there is no effective alternative, apple growers annually apply 3 sprays of organophosphate insecticide in July and August to control apple maggot and 3 sprays of organophosphate insecticide in May and June to control plum curculio (no other insecticides are as effective). This represents more than 75% of all insecticide applied annually to apple trees in much of the Northeast.
There is only one alternative approach that has been demonstrated to have potential in providing commercial-orchard control of apple maggot nearly equal to that provided by organophosphate sprays: placement of a single odor-baited sticky red sphere (=a highly attractive odor/visual mimic of an apple) on every perimeter apple tree in an orchard to intercept apple maggot flies immigrating into orchards from infested unmanaged host trees outside of orchards (very few flies originate within orchards). This proposal aims to evaluate various patterns of deployment of odor-baited spheres for apple maggot control. Information obtained will serve as a guide toward optimal patterns of sphere deployment using minimal numbers of spheres to achieve effective apple maggot control in orchard blocks of a given tree size, cultivar composition and fruit load. Specifically, during the first 2 years, we plan to evaluate different amounts of synthetic fruit odor, different numbers of sticky spheres and different arrangements of odor-baited sticky spheres on perimeter apple trees for their ability to intercept color-coded apple maggot flies released onto trees in areas bordering commercial orchards. For the third year, we plan to validate patterns of sphere deployment judged (from information obtained during the first 2 years) to be optimal for controlling apple maggot flies in blocks of small vs. medium-size commercial orchard apple trees consisting of cultivars of low vs. middle vs. high susceptibility to apple maggot. In addition, for the third year we plan to substitute pesticide-treated biodegradable spheres (coated with a very small amount of safe pesticide) for sticky spheres as fly-controlling agents. The end result should be a bio-based system of apple maggot control that is a simple, reliable and affordable alternative to organophosphate sprays, and whose deployment can be tailored to specific characteristics of any orchard block. For plum curculio, there is an urgent need for attractive odor/visual traps that can be used first for the purpose of delineating locales in orchards which do and do not require spray treatment against curculios, and second which can be used to directly control curculios in a way analogous to that of traps used for apple maggot control. Like apple maggot flies, nearly all plum curculios immigrate into orchards from sites outside of orchards, few arising within orchards. During the first 2 years, we plan to evaluate (in commercial orchards) traps comprised of known attractive odor and visual stimuli for the ability of trap captures to reflect damaging vs. non-damaging populations of curculios. Also, during the first 2 years, we plan to develop a multivariate regression model for predicting the optimal timing of sprays against curculios should trap captures indicate populations requiring treatment. For the third year, we plan to validate use of traps in conjunction with the predictive model for determining need and timing of curculio control in blocks of commercial orchard trees. Finally, in both the second and third years, we plan to apply the approach used to date for bio-based apple maggot control and place attractive odor/visual traps for plum curculios on every perimeter tree of small blocks of apples in commercial orchards and evaluate their ability to directly control curculios in the absence of insecticide sprays. This would be an essential first step toward eventual large-scale control of plum curculio using traps. Objectives: Objective 1. Optimization of patterns of deployment of odor-baited spheres for direct control of AM flies in commercial apple orchards. A. Optimization of amounts of attractive synthetic fruit odor per tree (Year 1). B. Optimization of numbers of spheres per tree (Year 1). C. Optimization of patterns of odor-baited sphere deployment in blocks of trees (Year 2). D. Validation of optimal patterns of odor-baited sphere deployment for AM control using pesticide-treated spheres (Year 3). Objective 2. Development of models for predicting optimal timing of sprays against PC; evaluation of traps for monitoring and pinpointing PC abundance and for directly controlling PC. A. Development of multivariate regression models for predicting optimal timing of sprays against PC (Years 1 and 2). B. Evaluation of traps for monitoring PC abundance (Years 1 and 2). C. Evaluation of traps in combination with predictive models for pinpointing location and timing of sprays against PC (Year 3). D. Evaluation of traps for direct control of PC (Years 2 and 3). We anticipate that completion of Objective 1 on AM will provide commercial apple growers throughout the Northeast with sufficient information for direct control of AM by odor-baited pesticide-treated spheres in an effective, reliable and economic manner. We anticipate that completion of Objective 2 on PC will provide apple growers (and possibly also growers of other sorts of tree fruit) throughout the Northeast with sufficient information to permit substantial reduction in insecticide use against PC primarily by offering an effective, reliable and economical means of pinpointing locales and times at which insecticides are and are not needed for control, and secondarily by offering a potential means of direct control of PC using odor-baited visual traps. Problem, Background and Justification Importance of Tree Fruit in the Northeast Tree fruit are among the most widely grown and economically valuable crops in the Northeast. Apples are grown in all Northeast states (CT, DE, MA, ME, NJ, NH, NY, PA, RI and VT) and constitute the most economically valuable tree fruit crop in the region. Latest estimates by the USDA show annual apple production in the Northeast to be about 46 million bushels, with a value exceeding 400 million dollars. The combined value of pears, peaches, nectarines, and plums exceeds 150 million dollars annually in the Northeast. In all, about 6000 growers are involved in tree fruit production in the Northeast. The value of all tree fruit produced in the Southeast (5 states) and Midwest (12 states) is about the same as that of all tree fruit produced in the Northeast: 600 million dollars annually. Importance of Apple Maggot and Plum Curculio as Pests The apple maggot (AM), Rhagoletis pomonella (Walsh), is a key pest of apples throughout the Northeast region as well as in the Midwest. It is less troublesome in the Southeast but has become established and poses a steadily increasing threat to apple production in all West Coast states. It is not known to occur on any other continent. It is native to the Northeast, the native host being hawthorn. About 150 years ago it expanded its host range to include apples and to a much lesser extent pears, both of which were introduced to the USA by Pilgrims in the 17th century (Bush 1966). Egglaying and larval feeding in fruit occur into harvest time in September. If some form of control is not applied against AM, injury resulting from larval feeding in the fruit flesh is usually very extensive. For example, samples of fruit from unmanaged apple trees in Massachusetts taken annually since 1978 have never shown less than 95% of fruit injured by AM (Prokopy 1990 and unpublished data). Similar data were obtained in New York in the 1960s (Glass and Lienk 1971). The plum curculio (PC), Conotrachelus nenuphar (Herbst), is a key pest of all tree fruit in the Northeast, Southeast, and Midwest. It is not known to occur in the Northwest or on any other continent. It is a native of the Northeast, its native host being wild plums. About 200 years ago it expanded its host range to include apples, pears, nectarines, and cultivated plums. On unmanaged fruit trees in the Northeast, PCs annually damage a majority of the developing fruit. To illustrate, samples of fruit at harvest from unmanaged apple trees in Massachusetts taken annually since 1978 reveal no less than 86% injured fruit in any year and an average of 94% injured fruit across all years (Prokopy 1990 and unpublished data). Similar data were obtained in New York in the 1960s (Glass and Lienk 1971). Grower surveys indicate the importance of AM and PC to the viability of commercial tree fruit operations. To illustrate, in 1995 an extensive survey was sent to all commercial tree fruit growers in CT, MA, ME, RI and VT as a component of the USDA National Initiative Phase I IPM Planning Grant Process. Percentages of growers responding to this survey were as follows: CT= 60%, MA= 70%, ME= 41%, RI= 65%, and VT= 52% (growers from the remaining New England state - NH - were not surveyed). Results merged across participating states showed that when growers were asked how important each of 22 insect, disease and weed pests were in their orchards, PC ranked first in importance, apple scab second, AM third and mites fourth (importance here is defined as a combination of very important and somewhat important) (Prokopy et al. 1996a, Coli 1998) (see Appendix for documentation). Across recent annual meetings of the Massachusetts Tree Fruit IPM Advisory Committee (50% of the Committee is comprised of growers), PC, AM, and mites have dominated as the arthropod pests of the greatest concern and of greatest expressed need for development of viable biologically-based alternatives to pesticide as the principal means of control. General Biology and Current Control of Apple Maggot As described by Dean and Chapman (1973), AM overwinter as pupae in soil beneath host trees (principally apple and hawthorn) and emerge as adults in June, July or August. After feeding for a week on bird droppings and insect honeydew, adults become mature and are ready to lay eggs, which average 300 per female. At this point, adults are highly prone to leave the area where they emerged and to emigrate from considerable distances (up to a mile) into apple orchards. There, females search for fruit into which to lay eggs. AM flies rarely originate from fruit within commercial orchards. Very rarely is there more than one generation per year. To control AM, growers threatened by this pest annually apply an average of 3 insecticide sprays (Reissig 1988, Prokopy et al. 1990) to their entire orchard, beginning in early July and ending in late August. If sufficient pesticide residue is not present throughout the immigration and egglaying period of AM, injury to fruit may occur. In New England, New York and Michigan in particular, and to a lesser extent in apple production areas south of these states, AM is frequently the sole fruit-injuring pest active after June against which insecticide is applied to apple orchards. Indeed, in a 1991-1994 study by Prokopy et al. (1996b) in which no insecticide was applied in 10-acre blocks after early June over 4 consecutive years in several Massachusetts apple orchards and in which AM was controlled by traps, no insect, save lesser appleworm, emerged as a significant threat to fruit production and quality. Lesser appleworm can be controlled by Bacillus thuringiensis and spinosad. Codling moth and leafrollers never built to unacceptable levels. Several studies have been conducted on toxicants most effective against apple maggot flies (e.g. Bancroft et al. 1974, Pree et al. 1976, Reissig et al. 1980, Mohammad and Ali Niazee 1990, Duan and Prokopy 1995a, Hu and Prokopy 1999). By far the most toxic materials at lowest doses are the organophosphates azinphosmethyl, phosmet, dimethoate and chlorpyrifos, with the organophosphates diazinon and malathion of somewhat lesser toxicity. Still lesser in toxicity and of relatively poor effectiveness are the carbamates methomyl, oxamyl, and carbaryl; the chlorinated hydrocarbon endosulfan, and the synthetic pyrethroids permethrin and fenvalerate. Except for materials newly registered for application to apples, the above insecticides constitute the current array of insecticides available to apple growers for AM control. If any of the poorly-effective materials were to be used, applications would have to be very frequent, thereby defeating progress toward IPM. Among newly registered insecticides for orchard use (imidacloprid, avermectin, neem, spinosad, fenoxycarb, tebufenozide), certain of these have proven very toxic to AM flies under laboratory conditions but none has proven to be even moderately toxic to AM flies immediately after spraying on trees or toxicity is lost within a day or two after spraying owing to virtually complete absorption of the active ingredient into foliage and fruit. That is why none of these new materials is registered for use against AM. For decades, essentially all growers have been using an organophosphate insecticide to control AM. If one multiplies the number of acres of apples in New England, New York, Michigan and Wisconsin (states where AM is of paramount importance and that have about 150,000 acres under apple production) by the per acre average amount of active ingredient of organophosphates annually applied to control AM (2.1 pounds) (Coli, unpublished data), then the total amount of organophosphate annually used to control apple maggot in these states alone is about 315,000 pounds a.i. General Biology and Current Control of Plum Curculio As described in a review by Racette et al. (1992), damage to tree fruit by PC arises when PC adults feed upon and oviposit in developing fruit. Damage may be initiated as soon as petals fall from apple or pear blossoms or as soon as surrounding shucks fall away from peach, nectarine, and plum blossoms. Feeding injury occurs as a small cavity in the fruit, whereas egglaying injury appears as a crescent-shaped scar on the surface of the fruit. Injured fruit may (1) fall to the ground within 1-2 weeks after initial damage, (2) remain on the tree for 3-5 weeks until larvae become nearly mature and the fruit falls, or (3) remain on the tree until harvest and exhibit depressions accompanied by scars on the fruit surface, causing rejection for sale as fresh fruit. It is the fruit that fall to the ground 3-5 weeks after eggs have been laid that give rise to the next generation of adults, which emerge from pupae formed in the soil nearby infested fallen fruit. In the Northeast, there appears to exist exclusively what has been termed the northern strain of PC (Chapman 1938), which has one generation per year. Studies by Lafleur et al. (1987) and Lafleur and Hill (1987) in Quebec have shown that nearly all PC adults that arise in August from larval-infested fruit move from beneath orchard or unmanaged host trees to surrounding woods in autumn, overwinter there, and return to orchards or unmanaged host trees the following spring. Return movement usually coincides with the availability of developing apple fruit that provide essential food and oviposition sites. Nearly all PCs that attack orchard fruit in spring appear to originate in abandoned host trees outside the orchard. Such adults are capable of moving several hundreds of meters both when leaving and when reentering orchards in spring (Lafleur and Hill 1987; Prokopy, unpublished data). After arriving in orchards in spring, immigrating PCs periodically (sometimes even daily) move back and forth between canopies of the trees and ground beneath trees (Racette et al. 1991; Chouinard et al. 1993). Growers in the Northeast usually apply 3 sprays of insecticide annually to control PC (Prokopy et al. 1996b, Reissig et al. 1998). Either all 3 applications are made to the entire orchard or 2 applications are made to the entire orchard and 1 application to perimeter trees only (Chouinard et al. 1992a; Vincent et al. 1997). Much insecticide used to control PC is wasted when it is applied either to the entire orchard area or to the entire orchard border area, when in fact PCs and injury to fruit by PC are known to be highly aggregated in distribution (Racette et al., 1992). Among insecticides, only the organophosphates azinphosmethyl, phosmet and chlorpyrifos provide a level of PC control acceptable to most fruit growers (Anonymous 1997). Synthetic pyrethroids are less effective, lead to severe outbreaks of mites, and thus create as many problems as are solved by their use. Carbamates and all other known classes of insecticides discussed above under AM do not provide reliable control of PC. If one multiplies the number of acres of apples in New England, New York, Michigan and Wisconsin (states where PC is of paramount importance) by the per acre average amount of active ingredient of organophosphate annually applied to control PC (2.0 pounds) (Coli, unpublished data), then the total amount of organophosphate annually used to control PC in these states alone is about 300,000 pounds a.i. Biologically-Based Alternatives to Apple Maggot Control What are the potential alternatives to pesticides for controlling AM? Prokopy and Mason (1996) reviewed this subject and concluded from the existing literature and their own experience that none of the following approaches represent feasible alternatives. By colonizing apples as a new host, AM has effectively escaped all of its natural enemies, which have been unable to shift from hawthorn to apple. Hence, the prospect for effective biological control is poor, especially given the very low threshold for acceptable level of AM injury (0.5-1.0% of injured fruit). Cultural control through a habitat management approach of removing wild host trees up to 1.5 km from commercial orchards (the distance over which an AM fly can travel) is not feasible because few growers own or otherwise control land at such a distance. Host plant resistance also is an unlikely alternative to pesticides because cultivars that are of high customer appeal are at least moderately, if not highly, susceptible to fly oviposition and larval development. Indeed, there is little likelihood that host fruit tolerance or resistance will play an important role in AM management because selection of apple cultivars for planting is based largely on consumer appeal. Moreover, the apple tree produces fruit (flesh surrounding the seeds) to advertise seeds to potential vertebrate consumers (e.g. deer, birds), which carry the seeds away from the mother plant. To be palatable to a consumer, fruit flesh must be free of bitter or sour chemicals (the type which most often are responsible for insect resistance). The sterile male release approach, effective against Mediterranean fruit flies, has very little chance of succeeding against AM because AM females copulate many times (even daily) throughout life. Creation of fly free zones (as has been effective against Caribbean fruit flies) might be feasible in some parts of West Coast states, where AM is a recent introduction and not yet broadly established. But there is little prospect of this approach being effective in eastern and midwestern states, where flies are so numerous on millions of wild host trees. Behavioral control through application of synthetic egglaying deterring pheromone is a very distant future possibility but awaits pheromone identification and synthesis. What then is a feasible alternative to pesticidal control of AM? For the past 25 years, Prokopy and associates have been working on behavioral control of AM using red spheres as traps to capture or otherwise kill alighting AM flies (progress reviewed in Prokopy and Mason 1996). Red spheres of 8-cm diameter are super-normal visual mimics of ripe hawthorn and apple fruit and are highly visually attractive to apple maggot flies. When coated with sticky (e.g. Tangletrap) and hung on all trees in an apple orchard at the rate of 2-6 per tree (depending on tree size), they can provide 99% control of the flies. The problem with this approach is the very large number of traps required to achieve control. With the identification of attractive apple odors by Reissig, Averill, Roelofs and colleagues at Geneva, New York (Averill et al. 1988), the way was paved for a new approach to using the spheres: placing spheres baited with synthetic apple odor only on perimeter trees in an apple orchard. By so doing, immigrating AM flies could be attracted to the odor-baited trees and to the spheres hung on such trees. This approach was evaluated extensively in 10-acre blocks of 6 Massachusetts commercial apple orchards from 1991-1994 (funded in part by a Northeast Region IPM grant) using butyl hexanoate as the synthetic fruit odor attractant and sticky-coating to kill flies alighting on the spheres (Prokopy et al. 1996b). Odor attractant and spheres were used at the rate of 16 per acre (i.e. they were about 5 meters apart on perimeter orchard trees). The results were highly encouraging: an average of 1.1% injury to fruit across the 4 years using traps compared with an average of 0.7% injury to fruit across the 4 years in nearby blocks treated with 3 organophosphate insecticide sprays. Two principal shortcomings arose, however, from the odor-baited sticky sphere approach. First, sticky spheres proved very messy to deploy and maintain on such a large scale, with few participating growers willing to adopt this method until an alternative to sticky was found as the fly killing agent. Second, to maintain fly-capturing effectiveness, sticky spheres needed to be cleaned of accumulated flies and debris every 2 weeks, a costly and laborious process. Fortunately, red spheres are highly selective and attract very few beneficial insects. What might be an effective and inexpensive alternative to sticky as a killing agent of AM flies alighting on red spheres? Anticipating in 1992 the need to develop such an alternative, we conceived the idea of coating the spheres with a mixture of insecticide, fly feeding stimulant and residue extending agent. We knew from our preliminary studies that most alighting AM flies could in fact be killed by direct contact alone with a coating of insecticide on a sphere, but the dose required to achieve kill of at least 90% of those alighting was 50 times or more greater than the dose required to kill flies which ingested pesticide together with feeding stimulant. Our aim was to use the lowest possible effective dose of insecticide on a sphere. After 6 years of research investigating virtually all labeled orchard insecticides (see Duan and Prokopy 1992, 1993, 1995a, 1995b, Wright et al. 1997, Hu and Prokopy 1998, 1999, for results), we have found that imidacloprid (Provado) at 2% active ingredient (the most effective insecticide found and the lowest dose achieving 90% kill of alighting AM) in a mixture of 20% sucrose (the most effective AM feeding stimulant found) and 70% Glidden Gloss Enamel latex paint (the most effective residue-extending agent for imidacloprid found) applied to the surface of a sphere killed at least 90% of alighting AM even after 3 months of exposure to outdoor weather, provided that sufficient sucrose was present on the sphere surface. That imidacloprid proved to be the most effective insecticide in paint against AM was somewhat surprising to us in that it is essentially ineffective against AM when applied to trees, being absorbed rapidly by foliage (Hu and Prokopy 1998). We have extensively experimented with numerous different approaches (summarized in Hu et al. 1998) to maintaining a continuous supply of sucrose on the sphere surface (rainfall as little as 5 mm washes away all sucrose from the above mixture applied to spheres). By far the most effective approach is that of constructing the entire sphere body from a mixture of fructose and sucrose (40%), corn flour (16%), wheat flour (16%), glycerol (8%), corn starch (5%), cayenne pepper (5% - to deter rodents from consuming spheres), sorbic acid (1% - to deter growth of microorganisms) and water (9%) (Hu et al. 1998, Wright et al. 1998). After shaping, such a sugar/flour sphere is heated in an oven for drying, following which it is sent to the user (scientist or farmer), who would coat it with latex paint containing imidacloprid. Our tests have shown that even after 25 cm of rainfall (well more than the average amount received during AM season in commercial orchards), sufficient sugar is available at the sphere surface (by virtue of seeping through paint) to effectively stimulate fly feeding. Such a sphere is cheap to produce (ingredients cost less than 50 cents) and will maintain its integrity until autumn, when through freezing and thawing, the surface starts to crack. During winter, the sphere completely biodegrades, with only a strand of holding wire remaining on the tree. These sugar/flour spheres were developed by us in conjunction with colleagues (Michael McGuire and Baruch Shasha) at the USDA lab in Peoria, Illinois. We hold a joint patent on their construction. At a recent meeting (November 11, 1998) between us and McGuire, McGuire agreed that his USDA lab would produce up to 2000 such sphere bodies free of charge for evaluation by us (and potentially other interested parties) in field trials in commercial orchards once a formula for sphere body composition has been finalized (by the end of year 2000 at the latest). Furthermore, Keith Dorschner of the IR-4 program (out of Rutgers University) communicated to us that he is working with the manufacturer of imidacloprid (Bayer Corp.) and the EPA to establish a label for use of imidacloprid-treated sugar/flour spheres for controlling AM (label should be in place for the year 2000) (see letter in Appendix). The remaining challenge is to refine approaches to deploying such pesticide treated spheres (PTS) in such a way that effective and reliable control of AM can be achieved under a variety of orchard conditions by use of a minimum number of spheres. Toward this end, for the past 3 years (supported by a USDA NRI grant which expired August of 1998), we have investigated effects of various factors on AM responses to sticky red spheres tested in commercial orchards. These factors have included within-orchard abundance of AM adult food (bird droppings and honeydew), addition of synthetic food-odor attractants (ammonia-type compounds) to spheres, size of tree canopy, and type of tree cultivar. Results (summarized in Reynolds and Prokopy 1997, Rull et al. 1997a,b, Reynolds et al. 1998, and unpublished data) indicate that neither abundance of AM food nor addition of food-odor attractants to spheres have any influence on the probability of capturing AM using spheres baited with synthetic fruit odor (butyl hexanoate), whereas tree size and tree cultivar do have significant effects. For example, among blocks of large, medium and small trees surrounded by odor-baited sticky traps at 1 trap every 5 meters along perimeter rows, more feral AM were found to penetrate into the interior of blocks of large trees (M7 rootstock) than medium trees (M26 rootstock) or small trees (M9 rootstock). Also, among the 13 most widely planted apple cultivars in New England, AM have shown greatest attraction/acceptance responses to certain early-ripening cultivars (e.g. Jersey Mac, Vista Bella), intermediate responses to certain intermediate-ripening cultivars (e.g. Gala, McIntosh) and low responses to certain late-ripening cultivars (e.g. Braeburn), although certain early-ripening cultivars (e.g. Paula Red) and certain mid-ripening cultivars (e.g. Empire) are of rather low attractiveness, and certain late-ripening cultivars (e.g. Fuji, Red Delicious) are of rather high attractiveness. Our aim for AM in this proposal is to conduct tests that will take us beyond the current standard method of applying 1 odor-baited sphere trap every 5 meters along perimeter rows. Specifically, we aim to conduct tests in commercial apple orchards that will guide us toward optimal patterns of trap deployment using minimal numbers of traps needed to achieve effective AM control in orchard blocks of a given tree size, cultivar composition and fruit load. Approaches to Reducing Insecticide Use Against Plum Curculio and Developing Biologically-Based Alternatives to Control To reduce insecticide use against PC from the current norm of 3 (or at the least 2) whole-orchard spray applications to a reduced amount of application that is precise according to both within-orchard location and timing of PC injury requires (1) an effective method of monitoring the abundance of PC adults at different locales within an orchard, and (2) an effective method of timing a needed spray when adults are deemed sufficiently abundant to merit application. With respect to monitoring abundance of PC adults, to date growers have been forced to rely on the appearance of PC egglaying scars as a sign that PCs have become active at a monitored locale and are an imminent threat to the crop (Prokopy and Croft 1994). Tapping PCs from tree branches onto a cloth is unreliable for this purpose (Vincent et al. 1997). As soon as the first scars are seen, growers spray immediately to prevent further injury. Thereafter, they usually spray twice more, 7-14 days apart on a calendar-driven basis, lacking any effective way of determining whether PC injury is present in a given locale or not. There is strong need for developing an effective means of monitoring PC abundance in orchards. To date, effective traps have been developed for monitoring numerous agricultural insect pests. These include several other species of weevils such as cotton boll weevils (Hardee et al. 1996), sweetpotato weevils (Smit et al. 1997), palm weevils (Oehlschlager et al. 1993), Sitona weevils (Neilson and Jensen 1993), pepper weevils (Riley and Schuster 1994), sugar cane borer weevils (Giblin-Davis et al. 1994), and pecan weevils (Tedders and Wood 1994). Several candidate trap types have been examined for monitoring PC adults. These include inverted polyethylene funnels hung beneath tree branches to capture falling adults (LeBlanc et al. 1981), unbaited sticky-coated apples or plastic spheres hung from host tree branches (Yonce et al. 1995), pitfall traps placed beneath host trees (Yonce et al. 1995), unbaited cotton boll weevil traps placed on vertical stakes between woods and commercial orchards (Yonce et al. 1995), cotton boll weevil traps baited with a component of synthetic male sex pheromone of PC (grandisoic acid) and placed on cut ends of vertical host tree branches (Eller and Bartelt 1996), and tall dark-colored unbaited (tree-trunk mimicking) pyramid traps topped with detachable conical boll weevil trap tops and placed between host trees at perimeter rows of orchards (Schmitt and Berkett 1995). Only the latter 2 types of traps have shown promise of capturing even small numbers of PCs. However, when tested at several different positions (next to orchard tree trunks, between canopies of orchard trees, between orchard borders and woods), unbaited black pyramid traps have proven completely ineffective in monitoring PC abundance in 48 blocks of commercial apple orchard trees in Massachusetts (Prokopy and Wright 1998, Prokopy et al. 1999a). In fact, for 3 consecutive years (1996-1998), as the season progressed, PC injury to fruit in locales having such traps successively increased whereas trap captures successively decreased; and total numbers of PCs captured in each locale bore no relation to total damage caused by PCs at those locales. As determined from extensive observations of the behavior of PCs in orchards (Prokopy and Wright 1998, Prokopy et al. 1999b), a principal reason why unbaited black pyramid traps fail as a means of detecting PC abundance is that such traps are effective only at temperatures of less than 20°C (when PCs enter trees by crawling toward and up tree trunks). At 20°C or greater (when most injury to fruit occurs), PCs enter trees overwhelmingly by flying directly into the tree canopy, bypassing tree trunks and trunk-mimicking pyramid traps. In tests to date, cotton boll weevil traps (yellow color) baited with grandisoic acid and placed in canopies of trees have fared no better than unbaited pyramid traps on the ground as an accurate monitor of abundance of injury-causing PC adults in commercial-orchard trees in Massachusetts (Prokopy, unpublished data) or Quebec (Chouinard, unpublished data), although there was some suggestion of effectiveness in tests in Michigan in 1997 (but effectiveness could not be repeated in 1998) (Coombs et al., unpublished data). To date, there has been no reliable source of grandisoic acid, possibly accounting for the above uneven test results obtained using grandisoic acid supplied from varying sources in ad hoc fashion. For use in 1999 and thereafter, IPM International Inc. will furnish high quality grandisoic acid for PC tests (see letter from Kirsch in Appendix). If findings on other weevils can be used as a guide, then the most effective trap for PCs would be an attractive visual trap baited with a combination of attractive synthetic pheromone and attractive synthetic host volatiles. Toward this end, we found in observations in 1998 that PCs in tree canopies are attracted toward vertical twigs and branches having host fruit, which they arrive at solely by crawling. In 1998 trials of twig-mimicking cylinder traps of various color and sizes, we found that black cylinders 40 cm tall x 8 cm diameter were more attractive than other sizes (Leskey and Prokopy, unpublished data). In addition, we conducted extensive laboratory and field assays of PC attraction to each of the 19 compounds found by collaborating chemist P.L. Phelan (Ohio) to be present in the odor profile of host plum fruit at the stage of development most attractive to PCs (2 weeks after bloom). Two of these 19 compounds (ethyl isovalerate and limonene) attracted 6-10 times more PCs than controls in orchard studies, whereas none of the remaining 17 compounds proved attractive (Leskey and Prokopy, unpublished data). The stage is now set for extensive evaluation of the capability of twig-mimicking black cylinders (capped by detachable boll weevil conical trap tops) baited with grandisoic acid, ethyl isovalerate and limonene for monitoring abundance of PCs in apple tree canopies in commercial orchards. In addition, "circle traps" attached to tree limbs and designed to intercept crawling PCs (Mulder et al. 1997) are also worthy of evaluation in combination with attractive odor for monitoring PCs in apple tree canopies. Just in case they might perform better when odor-baited than unbaited, trunk-mimicking pyramid traps also deserve evaluation for monitoring PCs. With respect to timing of needed spray applications against PCs (need based on captures of PCs in monitoring traps), to date the most advanced study linking the temporal distribution of PC injury to fruit (particularly oviposition injury) with the temporal pattern of weather conditions is by Reissig et al. (1998), who developed a degree-day based model for predicting PC injury. They recommended that residual insecticide coverage be maintained for 171 degree-days (base 10° C) after McIntosh petal fall. This model incorporates only temperature as a weather factor, however. Given previous studies showing that PCs are sensitive to moisture (Smith and Flessel 1968; McGiffen and Meyer 1986 |
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