The project evaluated several alternative methods for borer management in apple and peach orchards. Commercial apple and peach orchards with a history of borer problems were selected for establishing research plots. The efficacies of various combinations of mulch/nematodes/water were evaluated under trial conditions and the best combinations were applied in commercial orchards for practical field evaluation against a pesticide standard.
Surveys conducted during winter educational meetings (6 locations, about 400 growers) before the start of the program revealed significant initial grower interest in the results of this project, but at the same time very strong current reliance on pesticidal methods for the control of wood boring insects in fruit orchards. During the second year of the project commercial apple and peach orchards with a history of borer problems were treated with various treatments incorporating entomopathogenic nematodes. The applications of nematodes mixed in mulch to the trunk of trees provided comparable control of wood boring insects to the standard insecticidal borer management practices. However, the limits of commercial availability of viable nematodes and specialized equipment necessary to conduct treatments represent probably the most significant challenges for a wider grower adoption of this tactic. If application can be done by trained applicators, such solution should eliminate this obstacle. Also, a long time window during the growing season available for effective use of nematode application should be helpful for the development of this kind of service.
Over 400 growers participated in educational meetings throughout the program and 20 fruit blocks located at 6 farms participated in the practical application of nematodes. Unfortunately, this fell short of the 30 growers expected in the educational performance target. With a drastic increase in the number of applied broad spectrum insecticides needed immediately to control a new invasive pest, brown marmorated stink bug (BMSB), this softer and environmentally friendly approach to manage wood boring insects unfortunately limited growers attentiveness and acceptance of this new method.
The peachtree borer (PTB), Synanthedon exitosa (Say) is one of the two key wood-boring pests of Northeast peaches while the dogwood borer (DWB), Synanthedon scitula (Harris) is a dominant species affecting apples. Dogwood borer larvae feed inside burr knots, which develop on the exposed portion of clonal rootstocks, and frass on the burr knot surface is a sign of an active infestation. Pupal cases often protrude slightly from the tree and remain visible for up to a year after the adults have emerged. Females lay eggs on or near burr knots and are particularly attracted to trees with infested burr knots.
Feeding is initially confined to the burr knot, but may spread to healthy bark outside it. Larval feeding contributes to a slow decline of the tree resulting in reduced yields or even tree death. PTB has one generation per year in Pennsylvania and usually feeds on the inner bark and cambium tissue, causing reduced growth and yield, or, if the infestation is extensive, tree death. Borers have been reported as increasingly important contributors to the reduced vigor or loss of peach trees in Pennsylvania and New Jersey (Greene et al., 1986). Although PTB is more prevalent in the southeastern US, it has gained in pest status in the Northeast over the past 10 years. The larvae often develop beneath the soil surface, thus increasing the difficulty of controlling them with contact insecticides. In addition, PTB is a native North American species that utilizes several wild species of Prunus that commonly occur in wild surroundings of apple or peach orchards.
Most growers rely on insecticides to control borers. Moth captures in pheromone traps are used to assess moth activity and to predict the time of egg hatch. Trunk sprays are most effective when applied at the start of egg hatch – generally two weeks after the start of adult flight. Handgun application of insecticides is a costly and potentially a health-hazardous operation. In addition, there is currently only one registered insecticide that provides adequate control of the borer complex: an organophosphorous insecticide, chlorpyrifos. Another previously available option, a chlorinated hydrocarbon named endosulfan, was recently removed from the use on stone fruits, and will be also banned from use on apples in 2015.
The technique of broadcasting sex pheromones for direct control through mating disruption has become a major component of fruit IPM programs (Thomson et al., 1998). Pheromone-based mating disruption is also a highly promising management approach for controlling DWB and PTB.
Another borer management tool, entomopathogenic nematodes (epn) have been evaluated as biological control agents since the 1980s and there have been numerous success stories documenting their effectiveness (Adams and Nguyen, 2002). Furthermore, epn have been shown to be completely safe to non-target organisms and are approved for use in IPM and organic farming systems (Akhurst and Smith, 2002). Advances in mass rearing techniques have opened the door to commercial production and epn are readily available through many agricultural supply companies (Grewal, 2002).
Entomopathogenic nematodes are sensitive to UV light, rapid desiccation, and temperature extremes that can quickly kill them. Therefore, application methods that minimize environmental stress to the nematode greatly improves efficacy (Mccoy et.al, 2007). In our previous projects we have developed a novel method for epn application based on a weed management concept called ‘foam mulch’ (Masiunas, et. al. 2003) or ‘hydramulch’ (Warnick et. al. 2006) (JH Personal communication). Foam mulch is essentially a cellulose-based slurry that can be sprayed or drenched onto the soil (or tree base) to a desired thickness. The slurry dries slowly, allowing nematodes to reach borer galleries. The mulch is non-toxic and completely biodegradable.
Many different species of epn have been evaluated for commercial production and efficacy. The nematode Steinernema carpocapsae is one of the most hardy, easiest to mass produce, and efficacious against a wide range of insect pests (Kaya, 1985). S. carpocapsae has been shown to be very effective for borer control (Shapiro and Cottrell, 2006).
The main goal of this project was to develop and evaluate non-chemical borer management program that would reduce grower’s reliance on pesticides and provide effective options for organic/reduced pesticide imput fruit production. Furthermore, this project was intended to fill the gap in the available non-chemical options for controlling pests such as borers. A sustainable IPM programs for borers require the availability and application of multiple control tactics.
During the project we evaluated alternative borer management methods based on the use of entomopathogenic nematodes in commercial apple and peach orchards.
1. After completion of initial laboratory and field trials evaluating the success of survival of nematodes in various media and on various insect larvae we identified most promising treatments for evaluations in the field setting.
2. Grower survey conducted during multiple winter educational meetings before the start of the program revealed significant initial grower interest in the results of this project; however, survey’results also revealed very strong reliance on currently available methods based on pesticide applications for the control of wood boring insects in fruit orchards.
3. Commercial apple and peach orchards with a history of borer problems were identified for participation in the research plots. The number of sites and acreage increased over the course of the project, although due to limits associated with the application methods (specialized hydroseeder equipment) the number of treated acres did not increase as expected through the length of the project. Due to mostly small sizes of orchard blocks participating in the research with nematodes, mating disruption against either dogwood borer or peach tree borer was incorporated only at a limited basis into the project. However, it is expected, when nematodes will be used on a larger whole orchard scale, the mating disruption, as a supplemental tactic, will again be incorporated into borers management programs.
4. The efficacy of each evaluated treatment was evaluated in each treated orchard and adjustments in methods were made to achieve best borer management results.
During the 2012 and 2013 seasons, based on experience from previous two years of the project and direct inputs from involved growers, only mulch plus nematode treatment was identified as the most promising for possible implementation in commercial orchard settings. During the 2012 season the efficacy of nematode/mulch treatment was evaluated in four apple and three peach orchards while during the 2013 season the project was conducted in five apple and four peach orchards. The increase in the number of sites was associated with addition of new participants, previously not involved in the project activities. The main challenges with a broader utilization of this tactics were associated with the use of a single specialized mulch delivery tool (hydro-seeder) and limitations related to application time.
5. Multiple updates on the project progress were presented to growers during winter and in season educational meetings.
Performance target, experimental/research: Document the field effectiveness of mating disruption and entomopathogenic nematodes for the control of wood boring insects as well as develop the best practical methods to incorporate those techniques into pest control practices.
Research Target – The results of the applied treatments will serve as the evidence of program success (short term effect). Tests will provide directions for growers on the best ways of adopting procedures. The decrease in borer populations will be evident in nematode/MD treated blocks (long term effect). During the second year of the project borer control will be sufficient to eliminate the need for additional treatments (i.e., insecticides).
Performance target, educational: As a result of field demonstrations, presentations and publication of educational materials at least 30 new growers will incorporate mating disruption and entomopathogenic nematodes as primary tools for borer control.
With expected constraints related to the survival of nematodes in the orchard settings, preliminary tests were performed to evaluate survival of nematodes under various procedures. The model system used codling moth larvae as a surrogate for dogwood and peach tree borer larvae. Codling moth (CM) was chosen because we have years of experience raising this insect in the laboratory and we could produce large numbers of larvae when needed whereas dogwood and peach tree borers have proven to be more problematic for laboratory culture. The CM larvae seek small, protected spaces to pupate and strips of double-walled cardboard offer an ideal substrate. We have shown that cardboard strips containing these larvae can be stapled to the trunks of trees to mimic the natural galleries caused by dogwood and peach tree borer larvae. Our laboratory testing under controlled conditions has shown the entomopathogenic nematode Steinernema carpocapsae will infect and kill CM larvae as readily as dogwood borer larvae under the same conditions.
Three orchard trials were conducted during the 2010 season. Two experiments utilized surrogate codling moth larvae system to evaluate application methods and nematode survival. The third experiment was done in commercial orchards to evaluate the actual efficacy of S. carpocapsae to kill dogwood and peach tree borer larvae under natural growing conditions.
Experiment 1 and 2 utilized CM larvae: the first experiment started July 16th, 2010 while the second started September 28th. Both trials were located in apple orchard located in Biglerville PA. Each treatment was replicated three times on two trees per replicate for a total of 30 trees during first experiment and a total of 24 trees during the second trial.
The third trial started October 25, 2010 when various treatments were applied in two apple blocks and one peach block. Prior to setting up the experiment, each orchards was evaluated to identify borer infested trees.
The list of treatments applied during each experiment during the 2010 season is listed below:
Treat. 1 (Exp. 1, 2 and 3) – Mulch without nematodes (Mulch only).
Treat. 2 (Exp. 1, 2 and 3) – Nematodes without mulch (Nem only)
Treat. 3 (Exp. 1, 2 and 3) – Nematodes in mulch (Nem+mulch)
Treat. 4 (Exp. 1, 2 and 3) – Nematodes in mulch followed by supplemental water applications 24 and 48 hours post nematode application (Nem+mulch+H2O)
Treat. 5 (Exp. 1 only) – Nematodes in mulch and detergent (Nem+mulch+detergent)
Treat. 6 (Exp. 3 only) – Insecticide control using Assail at 8 oz/100 gal; applied at 1 gal per tree
Treat. 7 (Exp. 3 only) – untreated control
During the Experiments 1 and 2 all treatments were applied to the lower, about 10 inches high part the tree trunk at a rate of approximately 200,000 – 300,000 nematodes per tree. Treatment number 5 included 100 ml of household dish detergent to determine if the mulch could be made to foam to improve coverage. Mulch samples were collected 24 and 48 hours after application from the tree trunk and soil to determine if viable nematodes could be recovered. The July application (Exp.1) of experimental treatments was conducted under very unfavorable weather conditions for nematode survival. The temperatures were in the mid-nineties and under very low humidity. However, one of the reasons for setting the experiment up under these conditions was to determine if the mulch could provide protection for the nematodes when conditions were much less than optimal. During September applications temperatures were in the low sixties. Exp. 3 treatments were applied at a rate of approximately 200,000 nematodes per tree in the apple blocks and 400,000 nematodes per tree in the peach block. Trees treated with various treatments during the fall 2010 were evaluated for the presence of surviving nematodes in the spring of 2011. Bark and mulch were collected from all treatments and evaluated for the presence and the number of nematodes. If present, the samples of frass with or without larvae were also collected and checked for the presence of nematodes.
Mulch for application was prepared by combining two and a half 5-gallon buckets by volume of Easy Mix Mulch (Turbo Technologies, Inc. Beaver Falls, PA) with 180 mL Turbosorb (Turbo Technologies, Inc. Beaver Falls, PA) and 160 mL Witches Brew (Turbo Technologies, Inc. Beaver Falls, PA). The ready mulch mixture was incorporated into 50 gallons water in the tank of a 50 gallon Turbo Turf Hydro Seeder (model HS-50 P). Nematodes, S. carpocapsae, (25M EcoMask Spray, BioLogic Biocontrol Products, Willow Hill, PA) were added to ready mulch mixture as needed per treatment. The hydroseeder was kept continuously agitated to prevent settling of the mulch mixture. Nematodes (25 million per packet) were kept separate in a cooler and were added to the mulch shortly before application allowing enough agitation time for the nematodes to become thoroughly incorporated in the mixture. Nematode only (Nem only) treatments and supplemental water applications were made using a 3-gallon backpack sprayer (3 gal Solo backpack sprayer from Gemplers.com)
During the spring 2011 (May) samples were collected from 3 orchards (two apple and one peach) with various treatments applied during the fall of 2010 and nematode counts in mulch, bark and frass found on treated trees were completed.
A block of commercial apples and block of peaches were added to the trials and treated in May. The nematode data was collected in the fall 2011. Evaluated treatments included: Treat. 1 – Nematodes in mulch (Nem+mulch); and Treat. 2 – Nematodes in mulch plus water at 24 and 48 h after application. Unfortunately, no control (untreated) block was available for evaluation at this location. Treatments were applied using a vertically positioned fan nozzle on the hydroseeder hose aimed at the base of the tree. With practice, the opening and closing of the nozzle could be timed to deliver approximately one-third gallon of mulch around the base of each tree (approximately 167,000 nematodes per tree). On average, a tree with a circumference of 20 inches and mulch applied up to 10 inches on the trunk would receive approximately 800 nematodes per square inch of treated trunk surface.
During the fall of 2011 (last week of August), samples of soil, mulch, bark and/or frass were collected from experimental sites, including sites treated during the fall of 2010. If present, frass was collected from all trees as sign of borer feeding, while in the absence of frass, samples of mulch or bark were collected to assess the presence of nematodes. The bark samples were collected only from treatments on apples without mulch, while the soil samples were collected only from peach trees treated with nematodes, pesticides and control treatment. Samples of isolated nematodes from all treatments were utilized in a model system with codling moth larvae to evaluate the presence of entomopathogenic nematodes (late fall 2011).
Nematode Recovery and Bioassays: Techniques typically used for extracting nematodes from soil were modified to recover nematodes from mulch. Mulch samples were collected from the bark and soil near the base of treated trees. The samples were weighed and teased apart in water. The samples were transferred to Baermann funnels and allowed to soak for 48 hours before the nematodes were recovered. Extracted nematodes were transferred to petri dishes and counted under a dissecting scope at magnification of 40x.
Trials conducted during the 2012 and 2013 seasons.
During the 2012 season the efficacy of nematode/mulch treatments was evaluated in four apple and three peach orchards while during the 2013 season the project was conducted in five apple and four peach orchards. During the spring of both years, tree trunks were treated with nematodes and mulch treatment. The number of trees treated with nematodes varied from 90 to 660 trees per treatment. In each orchard, parts of the blocks or group of trees in adjoining orchard were designated as a control trees (from 80 to 400 trees). The grower standard borer management program (e.g., application of pesticides to tree trunk) was not used for the nematode treated trees. During the summer all treated and control plots were evaluated for a presence/absence of fresh frass produced by feeding borer larvae. In late August and September samples all detected possible borer feeding sites with borer’ frass (if detected) were identified and frass together with pieces of surrounding bark were collected from each affected tree. Collected samples were placed in small plastic cups (1.0 fl oz) and stored in refrigerator for further laboratory nematode counts as previously described.
During each year of the project the relative pressure from PTB and DWB was monitored in each orchard used for trials. Large plastic delta pheromone traps (Trece, Inc.) baited with pheromone lures of either dogwood borer (apples) or peach tree borer (peaches) were deployed in each orchard to monitor borer populations.
The main goal of experiments conducted during the 2010 season was to evaluate and develop the best strategies for orchard applications of entomopathogenic nematodes.
In the trial 1 (July 2010) mulch samples collected from the tree trunk and soil 24 hours after application were still moist to the touch but almost dry after 48 hours. After soaking each sample in water and teased apart we determined that all samples yielded some live nematodes but significantly fewer live nematodes were found after 48 hours than after 24 hours. This evaluation was not quantitative but only to determine if live nematodes were present. The cardboard strips with codling moth larvae placed on treated tree trunks were collected after four days and incubated in sealed plastic boxes for an additional 7-10 days. It was evident that some pupae had completed their development since there were adult moths present in the boxes and empty pupa skins in the cardboard. Results of this experiment documented that adverse environmental conditions at the time of application can severely impact the survival and efficacy of S. carpocapsae even if supplemental water was applied following application.
The results of the trial conducted in September 2010 were more optimistic and indicate that higher levels of larval infection can be achieved by applying nematodes at a slightly greater inoculum rate and under more favorable weather conditions. The outcome of both 2010 experiments strongly suggested the positive impact of mulch on survival of nematodes as CM larvae treated with a nematode / mulch application have a much higher infection rate than larvae from trees treated by nematodes alone.
The evaluation of samples collected from commercial orchards treated in late fall 2010 also strongly support the benefit of applying nematodes in the mulch mixture (Tab. 1) although the range in quantity of recovered nematodes was quite wide and often difficult to explain. While the number of nematodes in mulch treatment was always higher in FR blocks, the highest number of nematodes in CML block was observed in pesticide treated block. As the experimental treatments were applied according to grower suggestions, it is possible the pre-existing conditions and possible indigenous population of nematodes influenced the outcome of treatments.
The results of reapplication of evaluated treatments during the spring of 2011 at the same location as during the fall of 2011 and summer applications at a new site PD in both apple and peach blocks are presented in Tables 2 and 3. During this set of observations the mulch samples were collected from treatments using mulch and bark and/or soil samples from treatments without mulch (Tab. 2). A separate fresh frass only samples were also collected from all treatments and the nematode counts data is presented in Tab. 3.
Nematodes were detected in all evaluated treatments and in all sample types. It appears mulch naturally becomes infested with free-living nematodes that inhabit the environment. Our attempts to confirm the presence of S. carpocapsae among recovered nematodes indicated the mix population of nematodes. Using the CM model system we observed about 50:50 ratio of live and dead CM pupae and larvae. Dead larvae and pupae were dissected and determined to be infected with Steinernema carpocapsae. The presence of fresh frass at the tree trunk is an indication of an active borer infestation. Frass samples collected from tress within the same treatments also had very wide range of nematodes (Tab. 3).
During the 2012 and 2013 seasons based on application experience from previous two years and direct inputs from involved growers, only the treatment of mulch plus nematode was continued as the most promising for possible implementation in commercial orchard settings. During the 2012 season the efficacy of nematode/mulch treatments was evaluated in four apple and three peach orchards while during the 2013 season the project was conducted in five apple and four peach orchards. While the nematode treatments were located in blocks with relatively high borer populations, the control blocks were identified based on close proximity to treated blocks and on captures of moths in pheromone traps. In result, although it was not planned, in most cases the control blocks appeared to have lower borer pressure than block used for nematode tests.
During the 2012 season, the percentage of trees with fresh injuries were at a similar level and even in blocks with multiple applications of entomopathogenic nematodes no significant differences were observed in percentage of trees with fresh frass (Tab. 4). Also, the numbers of recovered nematodes from frass samples during both 2012 and 2013 season remained similar between nematode treated and blocks with insecticide control (Tables 5 and 6).
The PTB and DWB moth populations as monitored by the moth captures in traps baited with the sex pheromone also remained at similar levels between orchards located in clse proximity. The examples of cumulative average moth captures per trap per locations during the 2012 season are presented in Figs. 1a and 1b. The average cumulative moth captures for trap placed in locations utilized during the 2013 season are presented in Table 7.
The evaluated new approach to manage wood boring insects was presented to growers and ag-industry during multiple extension/outreach events. Examples of such activities include:
Mid-Atlantic Fruit and Vegetable Convention. 2010. Biological control of peach borer with nematodes. Slide presentation. Presenter John Halbrendt. Audience 120 people
PSU FREC Open House – 2010. Bio-rational pest management. Presenters: G. Krawczyk and J. Halbrendt. Audience 75 people. (On –site demonstration)
PSU FREC Grower Field Day. 2011. Borer control with entomopathogenic nematodes. J. Halbrendt. Audience – 170 people. (On –site demonstration)
PSU FREC Plant Protection Day. 2012. Controlling dogwood borer and peach tree borer with entomopathogenic nematodes. Audience- 55 people (On –site demonstration)
Mid-Atlantic Fruit and Vegetable Convention. 2013. Use of entomopathogenic nematodes for borer control. Slide presentation. Presenter John Halbrendt. Audience 90 people
Additional Project Outcomes
Impacts of Results/Outcomes
Trials conducted throughout the project provided valuable information for practical implementation of the results. Our approach utilizing mulch as the moisture holder surrounding the borer infestation sites proved to be effective for improving survival of nematodes. Also, the utilization of hydroseeder to deliver mulch and nematodes to the target area without harm to entomopathogenic nematodes proved to be a practical approach.
However, the real-world applications and data collection revealed challenges with the proposed methods and expected efficacy of tested treatments. The evaluation of results is extremely time consuming and provides difficult to evaluate spectrum of results.
The 2012 and 2013 grower trials in commercial orchards provided practical verification of efficacy of proposed application for entomopathogenic nematode S. carpocapsae. The application of nematodes mixed in mulch to the trunk of trees provided comparable control of wood boring insects as the grower standard insecticide based borer control practices. The limited commercial availability of viable nematodes and specialized equipment necessary to conduct treatments represent probably the most significant challenges for a wider grower adoption of this tactic. However, if application can be done by trained applicators, it should possibly eliminate this obstacle. Also, a long time window for effective use of nematode application should be helpful for the development of this kind of service.
Although the overall results of the project validated the comparable efficacy of nematode based control of wood boring insect with the current commercial standard of insecticidal control, the project did not achieve all expected outcomes and milestones. Although all experimental milestones were met or exceed, the final educational milestones defined as the number of early adopters did not reach expected 30 growers. Despite over 400 growers participating in the educational meetings related to the project, during the 2013 season, only 20 fruit blocks located at 6 farms participated in the practical application of nematodes.
The constraints related to the intensity of insecticidal control of a new invasive pest, brown marmorated stink bug (BMSB), interfered directly with growers’ ability and interest in using of softer, more environmentally friendly management of other pests. Until non-chemical options for management of BMSB will become available, growers have no option and have to rely on multiple, frequent applications of broad spectrum insecticides to manage BMSB. And under such scenario, the implementation of non-chemical control of wood boring insects by itself will not be able to improve the overall biological sustainability of the system.
While there is a strong potential for adoption of the nematode program by small scale or organic fruit growers, the direct economic analyze of associated costs is not positive for this technology. Under single orchard operation, the adoption of the new practice will be more expensive than current standard insecticide application. The estimated direct material cost associated with the use of nematodes and mulch significantly exceeds direct cost of insecticide application. Additionally, although the time for actual application is similar for standard and nematode method (similar trunk direct hand-gun application), the time required for preparation of nematode plus mulch mixture also exceeds the labor associated with current practices. The high cost of specialized application equipment (hydroseeder), unless the application is provided as an outside service, also reduce the economic viability of proposed technology.
The potential environmental benefit from the use of non-chemical method and environmentally friendly material can not be calculated due to small sizes of participating orchards.
The project generated wide interest among growers as documented by grower attendance during our outreach activities, although as indicated in the survey conducted at the beginning of the project, this bio-rational approach has to still win over the traditional, insecticide based management program. However, with very limited available options for borer control, especially for small growers for whom mating disruption is not a valid option, or organic fruit growers, the use of entomopathogenic nematodes represents a valuable option. The direct cost of application remains the most significant limiting factor for an embracing of this method. The commonly available farm equipment is currently not ready for the nematode applications, especially in combination with mulch. The purchase of a specialized hydroseeder constitutes a capital expense, at this moment considered not necessary. One of the growers participating in the project during the 2013 season, after initial applications in his orchard, requested the option to borrow the hydroseeder for later use on his farm.
The commercial availability of viable nematodes and specialized equipment necessary to conduct treatments represent probably the most significant challenges for a wider grower adoption of this tactic. However, if application can be done by trained applicators, it should possibly eliminate this obstacle. Also, a long time window for effective use of nematode application should be helpful for the development of this kind of service.
And as few growers stated “until BMSB (invasive pest) can be controlled only by using broad spectrum pesticides, the adult borers will also be controlled by the way”.
Areas needing additional study
The authors of this report believe a larger scale trial, minimum of 5 plus acres per side should provide additional validation of this method. The combination of borer mating disruption program with entomopathogenic nematodes should also provide very effective control of this group of pests. Also, with a good survival of nematodes in mulch, additional means (methods) of delivering these organisms to tree trunk, maybe without the need for the use of specialized not-farm equipment would increase the rate of adoption for this bio-rational approach of controlling wood boring insects.