Final Report for LS11-241
Project Information
Field research in Georgia and Florida peach orchards indicated that entomopathogenic nematodes (aka beneficial nematodes) can control lesser peachtree borer and peachtree borer at the same level as standard chemical insecticides. A sprayable gel formulation enhanced protection of nematodes for aboveground sprays against lesser peachtree borer, and in soil applications for peachtree borer control. Peachtree borer control with nematodes was achieved using various standard agricultural sprayers in both preventative and curative applications. Thus, entomopathogenic nematodes are excellent biological control agents for control of key borer pests; these results may be applicable to other cropping systems as well.
Our overall goal is to develop a sustainable management system for southeastern peaches. In this project we will tackle the two primary remaining research challenges to implementing entomopathogenic nematodes as a biocontrol agent for borer pests in peach; additionally, we will investigate the impact of the novel control tactics on the system. Specifically, our objectives are:
- To determine the optimum method of applying entomopathogenic nematodes for control of peachtree borer (on a commercial scale).
- To determine the optimum entomopathogenic nematode formulation for control of lesser peachtree borer.
- Assess the impact of biocontrol applications on natural enemy systems.
Two species of Sesiidae, the peachtree borer, Synanthedon exitiosa, and the lesser peachtree borer, Synanthedon pictipes are serious pests of peach (Prunus persica) and other Prunus spp. Both species cause severe damage through larval feeding on the cambium; the peachtree borer (PTB) feeds on the roots whereas the lesser peachtree borer (LPTB) feeds aboveground on the tree’s trunk and scaffold limbs.
In the Southeastern US, most PTB moths emerge during late summer and early fall (Johnson et al., 2005). Following oviposition, hatched larvae bore into the trunk near the soil surface and tunnel toward roots. Larvae overwinter in the host plant and (in the eastern US) complete development in about one year (a bivoltine population occurs in extreme southern Georgia and Florida). Trees of all ages are susceptible to PTB damage, but young trees with developing root systems are particularly sensitive (Quaintance et al., 1932). In fact, a single larva can seriously injure or kill trees in a newly-planted orchard.
Previously, LPTB was a minor pest but has recently become a primary peach pest in the Southeastern US. Regulatory-induced removal of certain organophosphates appears responsible for LPTB’s current major pest status. LPTB has multiple generations in the Southeast. Adult moths lay eggs on the trunk and scaffold limbs usually on any damaged bark surface (Cottrell et al. 2008). Larvae bore into, and feed in, the inner bark and cambium. In the primary southeastern production areas, LPTB injury routinely reduces vigor and causes substantial premature orchard decline with loss of yield, and dramatically-accelerated mortality of scaffold limbs and trees (Horton et al., 2008).
Current control recommendations for PTB and LPTB depend solely on intensive use of chemical insecticides (Horton et al., 2010), i.e., for PTB, a single post-harvest application (primarily the organophosphate insecticide chlorpyrifos) and for LPTB, multiple preventative applications that specifically target S. pictipes (e.g., chlorpyrifos application and pyrethroids). Due to continual regulatory and environmental concerns (National Research Council, 1989; Cohen, 2000), alternative pest control tactics must be developed. Entomopathogenic nematodes have potential as biocontrol alternatives for suppression of sesiid pests such as PTB and LPTB (Shapiro-Ilan et al., 2009; 2010). Indeed, these concerns have recently come into focus with a proposed ban on chlorpyrifos: http://www.usnews.com/news/politics/articles/2015/10/30/epa-may-ban-common-pesticide-used-on-fruits-and-vegetables
Entomopathogenic nematodes (genera Steinernema and Heterorhabditis) are natural biocontrol agents (Kaya and Gaugler, 1993). Infective juvenile nematodes (IJ’s), the only free-living stage, enter insect hosts through natural openings or occasionally through the cuticle (Adams and Nguyen, 2002). After entering the hemocoel, the nematodes release symbiotic bacteria, which are primarily responsible for killing the host (Adams and Nguyen, 2002). The nematodes complete one to three generations within the host after which IJ’s are released to search out new hosts.
Entomopathogenic nematodes control a variety of economically important insect pests such as various root weevils, white grubs, and fungus gnats (Grewal et al., 2005). Additionally, EPNs can cause high levels of mortality in a variety of sesiid borer pests including several Synanthedon spp. (e.g., Miller and Bedding, 1982, Begley 1990, Williams et al., 2002). Entomopathogenic nematodes are amenable to mass production, packaged in various formulations, and can be applied in aqueous suspension using most standard agricultural equipment including sprayers and irrigations systems (Kaya and Gaugler, 1993; Shapiro-Ilan et al., 2006). Consequently, EPNs have been incorporated into IPM programs in various crop systems (Grewal et al., 2005; Lacey and Shapiro-Ilan, 2008).
The research we have conducted prior to the start of the grant project provided strong evidence that EPNs can be successfully implemented as a biocontrol tactic for PTB and LPTB. Our research indicated that biocontrol of PTB and LPTB promises to be efficacious as well as economically feasible (Shapiro-Ilan et al., 2009, 2010). Given that it is critical to match the appropriate EPN species to each particular target pest (Shapiro-Ilan et al., 2002), our first step was to screen a variety of EPNs for virulence to PTB and LPTB in laboratory and small field trials. We determined Steinernema carpocapsae to be the nematode of choice for PTB and LPTB; S. carpocapsae caused the highest mortality in PTB and LPTB compared with ten other EPN species tested (Cottrell and Shapiro-Ilan, 2006, 2011; Shapiro-Ilan and Cottrell, 2006).
In field trials, S. carpocapsae provided high levels of PTB control in a curative or preventative approach. In a curative approach, i.e., a spring application directed toward an established infestation, 88% control of PTB larvae was obtained from a single application of S. carpocapsae (Cottrell and Shapiro-Ilan, 2006). Although curative treatments may contribute to protecting the tree and reducing subsequent populations, substantial damage from larval feeding will have already occurred leading to reduced vigor and/or tree death tree death (Johnson et al., 2005). Indeed, to avoid PTB damage, standard recommendations with chemical insecticides are focused on the PTB egg-laying period (Horton et al., 2010). Thus, to mimic the recommended preventative approach, and protect the trees from damage, we applied S. carpocapsae three times during the fall egg-laying period (Shapiro-Ilan et al., 2009). Results indicated that S. carpocapsae caused suppression of PTB damage at the same level as the chemical insecticide standard, e.g., < 10% damage during three years (Shapiro-Ilan et al., 2009).
Although results of our PTB field trials demonstrated extremely high levels of efficacy, all of the research was conducted on a small scale. Thus, the primary challenge remaining is to adapt the approach to a commercial grower scale. Research conducted thus far utilized relatively small plots (one tree constituted one plot) where conditions for nematodes were optimized (e.g., in terms of irrigation and avoiding sunlight) and the nematodes were applied manually using a watering can. Clearly manual application is not an option for commercial operations, and efficacy on an orchard scale must be determined. Fortunately, based on EPN use in other systems, and given our high levels of efficacy achieved in small-plots, expansion to orchard scale is highly feasible. EPNs are currently applied to other crops on a large scale using various sprayers (e.g., pressurized, hydraulic, air blast, electrostatic, boom, and mist-blowers) and irrigation systems (e.g., drip, microjet, sprinkler, furrow), and these application methods are used on commercial scale farms in diverse systems including orchard crops (Grewal et al., 2005; Lacey and Kaya, 2007).
Certainly, methodology used in other cropping systems can be adapted to the peach system; our goal is to develop the optimal approach for PTB control. The method of EPN application can affect efficacy (Shapiro-Ilan et al. 2006), and therefore the specific application parameters should be adapted to each system. We proposed testing three different promising methods: microjet irrigation, targeted trunk-sprayer, and boom sprayer (in the end microjet was not tested as this is not a common mechanism for the growers). Based on our research thus far, control of PTB using S. carpocapsae has been made an official recommendation for home orchard management (Horton et al., 2010). We anticipate that the crucial research we are proposing herein will expand that level of usage to commercial-scale growers across the Southeastern US.
Control of LPTB with EPNs presents a greater challenge than control of PTB. The challenge stems from EPN’s susceptibility to UV light and desiccation (Shapiro-Ilan, 2002; 2006). Given that LPTB attacks the tree above ground, applications for LPTB control can leave the nematodes vulnerable to harmful environmental conditions. Indeed, when EPNs were applied in aqueous suspension without any protective formulation, the nematodes failed to suppress LPTB (Shapiro-Ilan et al., 2010; unpublished data). To overcome the problem, we developed a unique improved formulation to protect the EPNs (Shapiro-Ilan et al., 2010). We screened a variety of candidate formulations, and discovered that a sprayable gel provided the best results. The sprayable gel was the only formulation that enabled S. carpocapsae to significantly suppress LPTB in consecutive field trials (insect survival was reduced to 0-30%) (Shapiro-Ilan et al., 2010). The gel, called Barricade®, is commonly used to protect houses or other structures from wildfire damage and promises to be economically feasible for implementation. Although we have established that the gel+EPN treatments hold excellent promise for LPTB control, a number of important questions remain such as 1) what is the optimum method of application 2) Are there other formulations that may provide even better results? Thus, in this project we tackled the remaining barriers preventing use of EPNs for LPTB control; we will determine the best protective formulation and optimum method of application.
This project promises to produce substantial environmental, economic and social benefits. Environmental benefits will result from reduced chemical inputs. Reduction of chemical pesticides is beneficial to the environment because chemical pesticides can be harmful to nontargets including humans and wildlife (DeBach, 1974). The proposed project will improve quality of life by helping farmers to control arthropod pests without risk of poisoning, and by providing a safer food supply for the public. Economic opportunities will be created by enhancing the biological control industry and peach production. Additional details regarding this project’s benefits and impact on sustainable agriculture are provided in the section “Sustainable Agriculture Relevance”.
The proposed research will contributes to sustainable agriculture by promoting ecologically and economically sound farming practices and facilitating diversity and stability in the targeted cropping system. The project fits into the specific goals of the SARE program by promoting good stewardship of the nation's natural resources through the development of profitable, sustainable farming methods. Furthermore, the project will improve farmer health and quality of life through the development of safe pest control tactics, and by providing replacement technology for chemical insecticides that have been or may be removed in the future due to regulatory considerations. Specifically, sustainability will be bolstered by enhancing beneficial natural enemy systems and increasing reliance on biological control.
Within a sustainable framework, reduction of chemical inputs is desirable (National Research Council 1989; Edwards et al., 1990). Chemical insecticides may cause secondary pest outbreaks, result in development of insecticide resistance, destroy natural enemies, and create hazards for humans and the environment (Debach, 1974). There are, worldwide, approximately one million human poisonings and twenty thousand deaths annually due to pesticides (Pimentel et al., 2008). As a result, US regulatory agencies have imposed restrictions on chemical pesticide usage. The passage of the Food Quality and Protection Act, in 1996, has led to accelerated restrictions and removal of chemical insecticides (Cohen 2000); thus, the need for alternative pest control measures has increased. Biological control using predators, parasitoids, or pathogens, can be an effective alternative for management of arthropod pests (Debach, 1974; Tanada and Kaya 1993). In contrast to chemical insecticides, biological control agents are generally not harmful to humans or the environment, and have minimal or negligible potential to cause resistance or harm non-target organisms (Coppel and Mertins 1977). In fact, entomopathogenic nematodes have an added benefit as biocontrol agents in that their application is exempt from EPA registration as a pesticide, adding testament to their safety.
The need to develop alternative management systems is particularly important for the southeastern peach industry. Among US agricultural commodities, peaches have consistently ranked among the highest in percentage of crop with detectable pesticide residues (Punzi et al., 2005). Consequently, pest management in peach systems is under intense scrutiny and, due to regulatory measures, the use of certain chemical insecticides, e.g., some organophosphates, has been prohibited. Nonetheless, commercial pest management in Southeastern US peaches continues to rely solely on chemical insecticides (Horton et al., 2010). Furthermore, it appears that insecticide regulatory changes for peach has caused a number of previously minor or secondary pests to increase dramatically in economic importance, e.g., LPTB, San Jose scale, Quadraspidiotus perniciosus, and white peach scale, Pseudaulacaspis pentagona (Horton et al. 2000). Thus, as environmental contamination, public health concerns, and regulatory restrictions persist, there is an increased need for holistic sustainable management solutions. The introduction of a biocontrol tactic into the historically chemical-intense peach management system of the southeastern US, presents a rare opportunity to foster sustainable agriculture.
In summary, our project was intended to provide long-term and short-term benefits that contribute substantially to sustainable agriculture. Additionally, our results will lead to major advances on a regional level (e.g., to southeastern peaches and other stone fruits grown in Southeastern US), but will also have broad implications for sustainable agriculture on a national level. Specifically, in the short-term, our research will lead to commercial implementation of biological control for two key pests, and enhancement of natural enemies in the southeastern peach system. In the long-term, fundamental knowledge regarding the impact of biocontrol implementation on endemic natural enemies will be useful to a broad array of scientists studying biocontrol, IPM, or basic ecology. Furthermore, the novel biocontrol formulation and application methodology we develop in this project will be applicable to other systems, e.g., for control of borers or other pests in various crops such as grapes, berries, apples, etc.
Cooperators
Research
Objective 1: Determine the optimum method of applying entomopathogenic nematodes (EPNs) for control of peachtree borer (on a commercial scale).
This objective was extensively addressed in three major experiments. In our first experiment, we compared application of nematodes to soil with and without irrigation, and with the sprayable gel, Barricade. In a second experiment, to address the issue of application method, we compared common equipment that commercial growers could use for nematode application including a boom sprayer, trunk sprayer and handgun. These application approaches have been used by growers to apply chemical insecticides for S. exitiosa control, and therefore we reasoned they could be easily adapted for nematode application. Both of these experiments were directed at applying EPNs as a preventative treatment in the fall (during peachtree borer egg-laying season), which is the same timing that growers use when applying chemical insecticides. The third experiment also tested the various application equipment, but was directed at a curative treatment applied in the spring to “clean up” any peachtree borer infestation that remained.
Experiment 1: The effects of irrigation and a sprayable gel
The experiment was conducted in peach orchards with treatment applications being made in 2012 and 2013 (two separate trials). In the first year of the experiment, applications were made in a commercial peach orchard in Fort Valley, Georgia. Peaches (Cresthaven variety) were two years old in 2012 and spaced approximately 5.49 m x 4.57 m. The soil was a loamy sand with the percentage sand:silt:clay = 70:20:10, pH = 5.7, and organic matter = 1.5% by weight. In the second year of the experiment, we were informed that the orchard had recently been sprayed with a chemical insecticide for control of S. exitiosa, and therefore a new location was used for the 2013 applications. The location was a peach orchard at the USDA, ARS, Southeastern Fruit and Tree Nut Laboratory in Byron Georgia; trees (June Prince variety) were seven years old and spaced 6.1 x 6.1 meters apart. The soil was a loamy sand with the percentage sand:silt:clay = 76:16:8, pH = 5.6, and organic matter = 1.0% by weight. Nematodes, S. carpocapsae (All strain) for all applications were cultured in vivo according to Shapiro-Ilan et al. (2002, 2014) and used within two weeks of emergence. Viability of nematodes upon application was > 95%.
In the first trial, treatments were applied on September 20, 2012. The treatments included nematodes applied with or without irrigation, or with Barricade (Barricade International, Inc. Hobe Sound FL) in lieu of irrigation. Chlorpyrifos (Lorsban®, Dow Agrosciences, Indianapolis, IN) was applied as a positive control in a manner commonly used by growers, i.e., a handgun application to the trunk base until runoff using a recommended rate of 29.57 ml of product per 3,785 ml water (Horton et al., 2014). Given that the experiment was conducted in a commercial orchard the grower cooperator requested that an untreated control not be included; thus, comparisons were made among treatments and the positive control. The experiment was arranged in a randomized complete block design with 4 blocks. Each treatment was applied to four consecutive trees within a row (4 blocks x 4 trees per plot = 16 trees per treatment) and one buffer tree was left between treatments (within a block). Blocks were separated by a minimum of 30 m.
Nematode treatments were applied by pouring 1,500,000 IJs in 100 ml of tap water to the base of a tree, which was immediately followed with 165 ml to water the nematodes in. In the treatment receiving Barricade, the gel was sprayed after nematode application to about 1.5 cm thickness in a 60 cm radius around the base of the tree; the application was made using the manufacturer’s spray device at the recommended rate (approximately 4% gel). For the nematode+irrigation treatment, approximately 165-800 ml of water was applied by handgun to runoff targeting a 12.7 cm radius around the trunk; irrigation was applied the day after application and then three times per week for two weeks thereafter (thus 7 additional irrigation events; the other treatments did not receive any additional irrigation). The amount of irrigation varied based on soil moisture (thus impacting the quantity required for run-off), and was within the recommended range of irrigation per unit area (Goldhamer, et al., 2001; Taylor and Rieger, 2005).
In the second trial, treatments were applied on September 25, 2013. The treatments and all other application parameters were identical to the first trial. Irrigation, however, was reduced due to a US Government shutdown and during this time federal employees were barred from entering federal facilities. Therefore, rather than seven additional irrigation events, trees in the nematode+irrigation treatment only received three additional waterings (on September 27, 2013 October 3, 2013 and October 5, 2013).
For both trials, treatment effects were assessed in the spring of the year following application, i.e., on April 15, 2013 for the first trial and on April 14, 2014 for the second trial. For each tree, the presence or absence of an S. exitiosa infestation was determined as described in Shapiro-Ilan et al. (2009). Briefly, soil was excavated to approximately 12 cm depth around the base of the tree and examined for signs of current infestation, e.g., larvae, active galleries and fresh frass exudates.
Experiment 2: The effects of application method (fall applications)
This experiment was conducted in a peach orchard at the USDA, ARS, Southeastern Fruit and Tree Nut Laboratory in Byron Georgia; containing trees (June Prince variety) that were 6 yr old (at the beginning of the experiment) and spaced 6.1 x 6.1 m apart. The soil was a loamy sand with the percentage sand:silt:clay = 76:16:8, pH = 5.6, and organic matter = 1.0% by weight (the plots were adjacent to the other experiment conducted in Byron, GA and hence soil analyses were the same). S. carpocapsae (All strain), which was used in all applications, was obtained from BASF (formerly Becker Underwood, Ames, IA), E-Nema (Schwentinental, Germany) or produced in vivo as indicated in the treatment descriptions below. Nematodes were used within 3 wk of receipt and viability upon application was > 90% for all treatments.
Methods of nematode application included the following equipment: boom sprayer (part # 45030051 with 140” 7 nozzle, Moose Utility, Janesville, WI), automated trunk sprayer (Anonymous, 2005), handgun (part # 45030048, Moose Utility, Janesville, WI), and watering can (2 gallon, ACE Hardware, Oak Brook, IL). The boom, trunk sprayer and handgun methods were intended for direct comparison to determine relative suitability for commercial grower use; thus all three sprayers utilized nematodes from the same source, i.e., BASF. However, to control for potential differences in commercial nematode products, an additional trunk sprayer treatment was made with nematodes obtained from E-Nema. The watering can treatment used nematodes that were produced in vivo in the Shapiro-Ilan laboratory (Shapiro-Ilan et al., 2002; 2014); this treatment was considered a positive control given that we had already demonstrated S. carpocapsae (All) produced in this manner and applied manually would suppress S. exitiosa damage (Cottrell and Shapiro-Ilan, 2006; Shapiro-Ilan et al., 2009). Application of chlorpyrifos (at the standard rate as indicated above) was also included as a positive control, and a non-treated (negative) control was also included. The experiment was arranged in a randomized complete block design with three replicate blocks. Each plot was situated in a separated row and contained seven trees (thus there were three blocks x 7 trees = 21 trees per treatment); the blocks were separated by a minimum of 18 m.
Treatment applications were made in two consecutive years (two trials): September 25, 2012 and September 26, 2013. The rate of application was the same as in the irrigation experiment, i.e., 1,500,000 IJs per tree. The amount of water used per tree for each application varied based on the nature of equipment (to achieve coverage without runoff) and was 800 ml for boom sprayer, 1600 ml for handgun, 800 ml for trunk sprayer, and 250 ml for watering can. Chlorpyrifos was applied via handgun as described in Experiment 1. After treatments were applied, all nematode plots were watered in the same manner and schedule as described in Experiment 1 (including the reduced level of irrigation in the second year of the experiment). The 2012 and 2013 treatments were assessed as described above on April 16, 2013 and April 16, 2014, respectively.
Experiment 3: The effects of application method (spring-curative applications)
This experiment was run essentially in an identical manner as experiment #2 except that treatments were applied in the spring in a curative approach. Damaged trees were identified and treatments were applied only to these trees. Subsequently the ability of treatments to kill the borers was assessed. Commercial nematodes were applied to existing PTB infestations via boom sprayer, handgun, or trunk sprayer; Also, non-commercial (lab grown) nematodes were applied via watering can was included. Chlorpyrifos and a non-treated control were also included. We assessed the % trees infested with PTB (if any live larvae were found it was considered infested) and also average number of live larvae per tree. The experiment was conducted at Lane’s commercial orchards in 2014and repeated at USDA, Byron station in 2015.
Statistical analyses
In Experiment 1 & 3, treatment effects within each year were determined separately using ANOVA (Proc GLM, SAS, 2002). Given that the second experiment (application method) was consecutively conducted at the same location, and the interaction between year and treatment was not significant, data from both years were combined and treatment effects were determined by ANOVA (Proc Mixed, SAS, 2002). In both experiments average percentage of infested trees per plot were arcsine transformed prior to analysis (Southwood 1978; Steel and Torrie 1980); non-transformed means are presented in the figures. If a significant model and treatment effect was detected in the ANOVA, then the treatment differences were further elucidated through Tukey’s test (SAS, 2002). The alpha level for all statistical tests was 0.05. For all experiments (and both years), average daily maximum and minimum ambient temperatures, and precipitation were recorded from the date of application until two weeks following the application.
Objective 2: Determine the optimum entomopathogenic nematode formulation for control of lesser peachtree borer.
This objective was extensively addressed through a series of experiments. The first 3 experiments (toxicity of adjuvants, use of lower Barricade gel concentrations, addition of sunscreens) were directed at developing an improved formulation to protect beneficial nematodes from harmful UV and desiccation. The 4th experiment was conducted as a practical application to test an improved formulation for efficacy in suppressing the lesser peachtree borer.
Experiment 1: Toxicity tests
The toxicity of several adjuvants to S. carpocapsae IJs was tested in the laboratory. Petri dishes (100 mm) lined with filter paper were used as experimental arenas. Approximately 5,000 S. carpocapsae IJs were applied to each arena in a 5% solution of each of the following ingredients: Barricade®, Yucca®, Waterlock Polymer®, Soyscreen oil, Soyscreen+Fantesk (oil:starch, 1:1), titanium dioxide (TD), or octyl methoxycinnamate (OMC). A treatment of Nemaprotect® was applied at 1% concentration. A control consisted of EPNs applied in 1ml tap water only. Dishes were stored at approximately 22-25ºC in the laboratory. After 30, 60, or 120 minutes exposure to solutions, IJ survival rate was assessed. Counts of 50 individual nematodes from each dish were made and percent survival was assessed by movement response when prodded with a dissecting probe (Kaya and Stock, 1997). The experiment was done as a completely randomized design. There were four replicates of each treatment and the control and the entire experiment was conducted twice in time.
Experiment 2: Direct sun exposure to EPNs in 1% and 2% Barricade®
The efficacy of EPNs in Barricade® solution was evaluated after sunlight exposure. Applications were made in direct sun and subsequently assessed in the laboratory. Tests were conducted at the Southeastern Fruit and Nut Research Station (Byron, GA). Approximately 1,000 IJs in 1ml a solution of 1% or 2% of Barricade® gel were applied via handheld spray bottle to 100 mm Petri dishes. An aqueous treatment containing EPNs and no gel was included as a control. A non-treated control of water-only (no EPNs) was also included. Replicates were exposed to direct sunlight for durations of 0, 15, 30, 60, and 120 minutes. Sunlight exposure assays were performed between May and August of 2014. Assays were performed at approximately 09:00h; ambient temperature for all tests was between 27-33° C. After exposure, dishes were brought into the lab and 10 G. mellonella last instars were placed into each dish for 30 minutes. Larvae were then moved to a new dish and incubated at 25° C. Host mortality was recorded at 24 and 48 hours. The experiment was done as a completely randomized design. There were three replicates of each treatment and the entire experiment was conducted twice in time.
Experiment 3: Direct sun exposure to EPNs in Barricade® plus UV protecting ingredients
Based on the results of the toxicity assays, two UV protectants, titanium dioxide (TD) and octyl methoxycinnamate (OMC), were used for continuing experiments. The UV-protection provided by TD and OMC when added to 1% Barricade® solution was tested in the laboratory and an outdoor environment. Approximately 1,000 IJs in a 5mL solution of 1% Barricade®, 1% Barricade® plus 1% TD, and 1% Barricade plus 0.1% OMC, and a control treatment of IJs in tap water alone were applied via handheld spray bottle to 100 mm Petri dishes. A non-treated control of water-only (no EPNs) was also included. Treatments were replicated as described in the previous assay, and outdoor exposures were done at the same time intervals. Sunlight exposure assays were performed at the Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA between May and August of 2014. Assays were performed at approximately 09:00h; ambient temperature for all tests was between 27-33° C. Each treatment dish was brought into the lab after exposure and 10 G. mellonella larvae were introduced into each dish in the same way as described above. Larval mortality was recorded at 24 and 48 hours. The experiment was done as a completely randomized design. There were three replicates of each treatment and the entire experiment was conducted twice in time.
Experiment 4: Field tests against lesser peachtree borer
The focus of this experiment was to determine if a lower concentration of Barricade®, when combined with EPNs, could be applied as a single application using standard spray equipment, and the combination would still be effective for control of S. pictipes (lesser peachtree borer). The advantage in applying a single spray with Barricade gel instead of the previously tested dual application (first nematodes then Barricade on top) is that the single spray greatly increases ease-of-use and costs for the grower. Additionally, in prior research we did not compare nematode applications to chemical insecticide treatments. Therefore, the second objective of this study was to compare the efficacy of nematode applications with chlorpyrifos.
The experiments were conducted in Quincy, Florida, at the University of Florida, North Florida Research and Education Center. Peaches (16-year-old University of Florida test variety M2-6 trees) were planted with a 4.5 x 6 m spacing in a fine sandy loam soil. The experiment was conducted in 2013 and repeated in 2014. Commercially produced nematodes, S. carpocapsae (All strain) were used in experiments. In 2013, nematodes were obtained from Becker Underwood (Ames, IA) and in 2014 from E-Nema (Schwentinental, Germany). Infective juvenile nematodes (IJs) were stored at 13 °C for < 2 weeks before use. Nematode viability was ≥ 95% in all experiments.
Four treatments and a non-treated control were included in the experiments. Three nematodes treatments, which were applied in aqueous suspension, included nematodes with a full rate of Barricade® (approximately 4%), nematodes with 2% Barricade®, and nematodes without Barricade®. The chemical standard, Chlorpyrifos was also applied as Nufos® 4E (44.9% a.i. Cheminova, Inc., Research Triangle Park, NC) in 2013, and Lorsban® Advanced Insecticide (40.2% a.i., Dow Agrosciences, Indianapolis, IN) in 2014. A non-treated control was included.
Treatments were applied to wounds infested with S. pictipes. Infested wounds were identified and marked prior to treatment application (Johnson et al., 2005). Approximately 20 ml of suspension was applied to each wound. For nematode applications, 1 million IJs were applied to each wound (in a suspension of 50,000 IJs per ml). Chlorpyrifos was applied at a recommended field rate (approximately 7015 ml per hectare). All treatments were applied as a single spray using a 7.6 l handheld pump sprayer (Ortho/Scotts company, Marysville, OH), except the Barricade® full rate was applied separately from the nematode suspension (applied immediately after as a cover spray) using a 94.6 l electric sprayer (“Dependable 12-Volt Standard 25 gal Sprayer,” Fimco Industries, Dakota Dunes, SD).
Treatments were applied on November 5, 2013 and October 14, 2014. Experiments were arranged in randomized complete block designs. In 2013 there were 4 blocks of 3 wounds per treatment, and in 2014 there were 6 blocks of 6 wounds per treatment. All wounds were either on the same tree or two adjacent trees, and there was a minimum of a two-tree buffer between each treatment. Treatment effects were determined by assessing the number of surviving S. pictipes in wounds (Shapiro-Ilan et al., 2010) 8 or 14 d post-application in 2013 and 2014, respectively; the bark over each wound was peeled back, the wound was searched, and the number of live or dead larvae was recorded.
Weather data was recorded for the period of nematode application until assessment of S. pictipes survival. Specifically, average daily mean, minimum, and maximum temperatures were recorded as well as relative humidity and precipitation. The weather station (from which data were obtained) is located on the University of Florida, North Florida Research and Education Center less than 0.6 km from the peach orchard used in the experiments.
Statistical analyses
In the first 3 experiments, data from repeated experiments were pooled. Data for IJ survival (from toxicity tests) or the G. mellonella mortality in the direct sunlight assays were subjected to ANOVA and significant differences among then treatments were further elucidated using the SNK test. All percentage data are arcsine transformed prior to analysis (Steel and Torrie, 1980). For the 4th experiment (field trials), treatment effects were analyzed with ANOVA based on average number of surviving S. pictipes per wound; if the F-test was significant (P ≤ 0.05) then differences were elucidated through the Student–Newman–Keuls’ test (SAS, 2002). The average number of live S. pictipes was square-root transformed prior to analysis (Southwood, 1978; SAS, 2002). Non-transformed means (± SE) are presented. Additionally, Abbott’s formula (Abbott, 1925) was used to estimate the percentage suppression of treatments relative to the non-treated control.
Objective 3: Assess the impact of biocontrol applications on natural enemy systems.
The prevalence of entomopathogens (entomopathogenic fungi and endemic or introduced beneficial nematodes) was monitored at application sites at the USDA-ARS orchards in Byron, GA and at Lane’s commercial orchards in Fort Valley, GA.
Training: SARE Students
This project was not a training grant. Nonetheless, some student training/mentoring in sustainable agriculture research was conducted via the SARE Young Scholar Enhancement Grant program. Young Scholar Enhancement Grants were received for this project in 2013 and 2014. A student from Fort Valley State University was selected for the scholar program each year: Rickola Smith was the 2013 Scholar and Rashaad Culver was the 2014 Scholar. The students were trained in research and methods in sustainable agriculture and conducted projects related to Objective 2 of the parent project.
Objective 1: Determine the optimum method of applying entomopathogenic nematodes (EPNs) for control of peachtree borer (on a commercial scale).
Experiment 1: The effects of irrigation and a sprayable gel
In Experiment 1, the 2012 application resulted in different levels of S. exitiosa infestation among treatments (F = 17.89; df = 3, 9; P = 0.0004) (Fig. 1). When nematodes were applied without irrigation, the treatment did not prevent high levels of S. exitiosa infestation (75% of trees were infested) (Fig. 1). The levels of infestation observed in the nematode+Barricade treatment and chlorpyrifos treatment were not significantly different from each other and were less than the level observed when nematodes were applied without irrigation. The nematode treatment with irrigation also caused lower infestation levels than nematodes without irrigation, but allowed a higher infestation level compared with the chlorpyrifos treatment (Fig. 1). Results from the 2013 application were similar to the 2012 application, and also indicated a high level of S. exitiosa infestation in the no-irrigation treatment, significantly lower infestation in the chlorpyrifos and Barricade treatments (which were not different from each other), and an intermediate level of infestation in the nematodes+irrigation treatment (F = 5.03; df = 3, 9; P = 0.0175) (Fig. 2). Average daily maximum and minimum temperatures from the time of application through two weeks post-application were 27.9 °C and 16.1 °C for 2012, and 26.3 °C and 14.5 °C for 2013. Total precipitation during the same period was 52.6 mm in 2012 and 7.4 mm in 2013; thus the amount of precipitation in the first year was more than 7X the amount in the second.
Experiment 2: The effects of application method (fall applications)
Treatment effects were detected in Experiment 2 (comparing nematode application methods) (F = 4.08; df = 6, 24; P = 0.0059) (Fig. 3). The interaction between year and treatment was not significant (F = 1.66; df = 6, 24; P = 0.1755). In the combined analysis (across years), lower S. exitiosa infestation was observed in all nematode treatments compared with the non-treated control except the handgun treatment (Fig. 3). No differences among application methods were observed, and all nematode treatments (including the handgun treatment) exhibited the same level of infestation as chlorpyrifos (Fig. 3). Average daily maximum and minimum temperatures from the time of application through two weeks post-application were 27.0 °C and 15.4 °C for 2012, and 26.7 °C and 14.1 °C for 2013. Total precipitation during this period was 53.3 mm in 2012 and 5.5 mm in 2013; thus the amount of precipitation in the first was more than 9X the amount in the second.
Experiment 3: The effects of application method (spring-curative applications)
In 2014, all treatments reduced the number of peachtree borer per tree relative to the non-treated control (P < 0.05; Fig. 4). All nematode treatments were superior to chlorpyrifos in suppressing the insect in 2014 (Fig. 4). In 2015, all treatments reduced the number of peachtree borer per tree (P < 0.05; Fig. 4), and the water can application caused greater suppression than chlorpyrifos (Fig. 4). In both years of the experiment, all methods of application were effective.
Objective 2: Determine the optimum entomopathogenic nematode formulation for control of lesser peachtree borer.
Experiment 1: Toxicity tests
In the laboratory percentages of living S. carpocapsae IJs after 30, 60, and 120 minutes of exposure were compared among treatments. Survival of IJs in Barricade®, TD, and OMC, were not significantly different from the water control at any of the exposures. Nemaprotect had lower survival (81-71%) than the control (95-93%) at both 30 and 120 minutes. The Soyscreen+Fantesk (oil:starch, 1:1) treatment had lower survival (76%) than the control (94%) at 60 minutes. After 120 minutes, the Soyscreen+Fantesk (oil:starch, 1:1) formulation had significantly lower IJ survival (71%) than other treatments (F=3.28; df=8,62; P=0.0035)
Experiment 2: Direct sun exposure to EPNs in 1% and 2% Barricade®
Both 1% and 2% Barricade® solutions were tested for their ability to protect S. carpocapsae IJ during sun exposure. The ability of the IJs to infect and kill a host after exposure to sunlight was compared among treatments. Host mortality after 24 hours of incubation was significantly higher for both 1% and 2% Barricade® solution (50-80%) than either aqueous nematode treatment or the water-only control (0-13%) after UV exposures of up to 30 minutes (F=6.15; df=3,19; P=0.0042) (Fig. 5; note other time periods not shown). In the secondary test, in which hosts were incubated for 48 hours, both 1% and 2% Barricade® resulted in higher host mortality (100%) than the controls (2-67%) (F=35.07; df=3,19; P=<0.0001) after exposure up to 15 minutes (Fig. 5; note other time periods not shown). All EPN treatments caused higher host mortality than the non-treated (water only, no EPNs) control. At 30 minutes, all EPN treatments caused higher mortality than the non-treated control (F=17.59; df=3,19; P=<0.0001) and the 2% Barricade® treatment caused the highest mortality (100%). At 60 minutes exposure to sunlight, the 1% Barricade® was the only treatment that resulted in higher host mortality (60%) than the non-treated control (F=4.43; df=3,19; P=0.016).
Experiment 3: Direct sun exposure to EPNs in Barricade® plus UV protecting ingredients
The ability of the IJs to infect and kill a host after exposure to sunlight was compared among treatments. For up to 30 minutes of exposure of IJs to direct sunlight and 24 hours of G. mellonella exposure to EPN treatments, neither TD nor OMC added to Barricade® provided a statistically significant benefit expressed as higher host mortality when compared with the aqueous EPN suspension or Barricade® only (no additional adjuvants) (F=0.81; df=4,24; P=0.5333) (Fig. 6). After 60 minutes of exposure, Barricade® with TD was the only treatment that resulted in higher host mortality (43%) than the non-treated and nematode only controls (2-3%); OMC plus nematodes was not different than the TD treatment (F=6.22; df=4,24; P=0.0014) (Fig. 6).
Experiment 4: Field tests against lesser peachtree borer
Treatment effects were observed in 2013 (F=4.06; df = 4, 52; P = 0.0061) (Fig. 7). Compared with the non-treated control, lower S. pictipes survival was observed in wounds receiving nematodes with Barricade® (2% or full rate) or chlorpyrifos treatments (Fig. 7). In contrast, S. pictipes survival in wounds receiving nematodes without Barricade® was not different from the control. No difference between the nematode + Barricade® treatments and chlorpyrifos treatments were detected (Fig. 7) and all three caused lower S. pictipes survival compared with the nematode treatment applied without Barricade®. Abbott’s formula indicated 55% control in the nematodes plus Barricade® full rate treatment, to 68% control in the nematodes plus 2% Barricade® treatment.
In 2014, treatment effects were also observed, but the S. carpocapsae application with 2% Barricade® was the only treatment that resulted in lower S. pictipes survival compared with the non-treated control (F=3.37; df = 4, 90; P = 0.013) (Fig. 7). The numbers of surviving S. pictipes in the other treatments (S. carpocapsae with a full rate of Barricade® or without Barricade® and chlorpyrifos) were intermediate between the number in the nematode treatment with 2% Barricade® and the control (Fig. 7). The nematode plus 2% Barricade® treatment cause 76% control according to Abbott’s formula.
Objective 3: Assess the impact of biocontrol applications on natural enemy systems.
Based on soil bating, the entomopathogens (fungi and nematodes) found in test plots indicated persistence through the application periods and some nematode recycling was detected through 35 days post-application. No substantial differences were detected among treatment plots except overall, nematodes applied via trunk sprayer showed higher persistence than the boom sprayer applications (F = 7.66; df = 6, 150; P > 0.0001).
Educational & Outreach Activities
Participation Summary:
Talks to growers or professional societies:
Shapiro-Ilan et al. February 2013: “Novel Management of Plum Curculio and Peach Borers”. South Georgia/North Florida Peach Meeting. Quitman, GA.
Shapiro-Ilan et al. February 2014: “Enhancing the Efficacy of Entomopathogenic Nematodes for Control of Peachtree Borer and Lesser Peachtree Borer” presented at the Peach County Peach Update, Byron, GA. February 4, 2014.
Shapiro-Ilan et al. November 2014 Suppression of Peachtree Borer and Lesser Peachtree Borer with Entomopathogenic Nematodes: Effects of Application Method and Formulation. ESA: Portland, OR Nov 15-19 2014 (Shapiro-Ilan, Cottrell, Horton & Mizell)
Shapiro-Ilan et al. January 2015: “Control of Peachtree Borer and Lesser Peachtree Borer with Entomopathogenic Nematodes: Effects of Application Method and Formulation”, Peach County- Peach Update, January 22, 2015, Byron, GA.
Shapiro-Ilan et al. March 2015: “Improving Microbial Control Efficacy of Entomopathogenic Nematodes in Orchard Systems” presented at the International IPM Symposium March 23-26, 2015, Salt Lake City Utah
Shapiro-Ilan et al. UPCOMING January 2016: Beneficial Nematodes Are Effective Control Agents for Peachtree Borers. (David Shapiro-Ilan, Ted Cottrell, Russ Mizell, Dan Horton, Dario Chavez & Jeff Cook)
Mizell, R. F. et al. (co-PIs). Arthropod pests and IPM of fruit and nut pests. 2013. NFREC Arts in the Park Field Day. Oct. ~100 people.
Mizell, R. F. et al. (co-PIs). Arthropod pests and IPM of fruit and nut pests. 2014. NFREC Arts in the Park Field Day. Oct. ~75 people.
Mizell, R. F. et al. (co-PIs). Arthropod pests and IPM of fruit and nut pests. 2015. NFREC Arts in the Park Field Day. Oct. ~40 people.
Mizell, R. F. et al. (co-PIs). 2013. Managing arthropods and other pests in the nursery and landscape. 37thAnn. Field Day and Workshop in Entomology. FAMU. Tall., FL, 4-XI-10. 2 hr, ~50 people.
Mizell, R. F. et al. (co-PIs). 2014. Managing arthropods and other pests in the nursery and landscape. 38thAnn. Field Day and Workshop in Entomology. FAMU. Tall., FL, 5-XI-10. 2 hr, ~50 people.
Refereed Papers:
Shapiro-Ilan, D.I., Cottrell, T.E., Mizell, R.F. III., Horton, D.L. and Abdo, Z. 2015. Field suppression of the peachtree borer, Synanthedon exitiosa, using Steinernema carpocapsae: Effects of irrigation, a sprayable gel and application method. Biological Control 82, 7–12.
Shapiro-Ilan, D.I., Cottrell, T.E., Mizell, R.F. III., Horton, D.L. Efficacy of Steinernema carpocapsae plus fire gel applied as a single spray for control of the lesser peachtree borer, Synanthedon pictipes Corresponding Author: Dr. David I. Shapiro-Ilan Submitted to Biological Control.
Dito, D., Shapiro-Ilan, D. I., Dunlap, C. A., Behle, R. W. Lewis, E. E. Enhanced biological control potential of the entomopathogenic nematode, Steinernema carpocapsae, applied with a protective gel formulation. Submitted to Pest Management Science.
IN Preparation: Shapiro-Ilan, D.I., Cottrell, T.E., Mizell, R.F. III., Horton, D.L. Curative control of the peachtree borer, Synanthedon exitiosa, using Steinernema carpocapsae.
Non-refereed:
Shapiro-Ilan, D. I. and C. H. Bock. 2013. Organic Methods for Control of Insect Pests and Diseases of Pecan and Peach. Webinar (e-Extension/e-Organic): http://www.extension.org/pages/66504/organic-methods-for-control-of-insect-pests-and-diseases-of-pecan-and-peach-webinar#.VTDwsfnF91Y
Grower Demonstration Trials:
- A grower demonstration trial was implemented for peachtree borer control at the Fort Valley State University peach orchard in Fort Valley, GA. Approximately 1.5 acres were treated with commercially provided nematodes (S. carpocapsae) based on our methods and results, and an equal area was treated with chlorpyrifos. The outcome indicated (as expected) a high level of control in both approaches. This demonstration and the subsequent one described below were undertaken with the assistance of University of Georgia county extension agent, Jeff Cook.
- A grower demonstration trial was implemented for peachtree borer control at Lane’s commercial orchard in Fort Valley, GA. Approximately 3 acres were treated with commercially provided nematodes (S. carpocapsae) based on our methods and results, and an equal area was treated with chlorpyrifos. The outcome indicated poor results in the nematode applications; it was later discovered that the grower applied Movento®, which is known to have nematicidal activity thus explaining the shortcoming.
Project Outcomes
The primary findings and outcomes of the project are as follows:
Peachtree borer:
- In fall-time applications (intended to prevent damage to the tree) the nematode, Steinernema carpocapsae, produced a high level of control against peachtree borer (Synanthedon exitiosa); the level of control was similar to the standard recommended chemical insecticide, chlorpyrifos.
- A sprayable gel, applied after nematodes to the soil, may be used in lieu of irrigation. This was the first report using the sprayable gel, Barricade® in soil applications.
- Efficacy when applying nematodes was achieved using various standard methods of application including a boom sprayer, trunk sprayer, handgun, or watering can.
- In curative, spring-time applications, Steinernema carpocapsae produced higher levels of control compared with chlorpyrifos.
Lesser peachtree borer
- The ability of Steinernema carpocapsae to control Synanthedon pictipes was assessed.
- Aboveground applications of S. carpocapsae were enhanced using Barricade® gel.
- The gel can be applied in a single spray mixed with nematodes or applied separately.
- The nematode+gel combination controlled the pest as well as the standard chemical.
- The gel formulation can be enhanced further by adding sunscreens, titanium dioxide (TD) or octyl methoxycinnamate (OMC)
The Primary Impacts of the Project:
- Established that beneficial nematodes can kill peachtree borers on a commercial scale at the same level of efficacy compared with standard chemical insecticides.
- Developed a new protective formulation for beneficial nematodes (based on a sprayable gel) that may be useful in a wide variety of cropping systems.
- Grower use has been initiated and we expect it will be expanded as the results continue to disseminate.
- As chemical insecticides, such as chlorpyrifos, face increasingly strict regulation, we expect that the need for safe and effective biological alternatives, such as beneficial nematodes, will increase as well.
Economic Analysis
To complement the field experiment evidence on the relative effectiveness of traditional chemical insecticides vs. application of beneficial nematodes for Peachtree borer suppression, an economic cost analysis was conducted. Using cost estimates from existing literature and from the researchers’ experience during the field trials, estimates of the fixed and variable costs involved in the different nematode and chemical application methods were constructed in order to compare and contrast their respective costs with their relative efficacy in the field. Since previous research has not sufficiently quantified the relationship between the degree of Peachtree borer infestation on tree mortality or fruit production, the economic analysis is limited to comparing costs across different suppression approaches without consideration of revenue impacts.
To calculate the costs for nematode vs. chemical suppression techniques for Peachtree borer, four nematode application methods (automated trunk sprayer, boom sprayer, handgun, and a watering can) were considered with and without irrigation in addition to the experimental application of Barricade in lieu of irrigation and traditional application of chlorpyrifos via handgun. Equipment, nematodes, Barricade, and chlorpyrifos costs were acquired from manufacturers. The labor efficiency for the different application methods were assumed to be constant and omitted across the different techniques based upon the experience of the researchers during the field trials.
The cost of equipment for applying nematodes vary substantially with the cheapest being a watering can ($7) followed by a handgun ($220), boom sprayer ($260), and trunk sprayer ($5000). It should be noted that the trunk sprayer is a custom-made piece of equipment that is not available in the marketplace through conventional outlets. Barricade, a gel originally developed for fire suppression, is applied using a garden hose applicator ($80) available from the manufacturer. Chlorpyrifos is applied using a standard handgun ($220). Although there is a significant spread in applicator equipment costs, based upon the field trials little or no difference in the effectiveness of the different equipment was found when applying nematodes. Given that most growers already own either a watering can, handgun, or boom sprayer, no biological support is found to justify growers purchasing an alternative piece of equipment if nematode pest suppression is adopted on their farm.
The costs of the pest suppression materials, entomopathogenic nematodes and chlorpyrifos (Lorsban produced by Dow Agrosciences), are similar per treated acre. Nematodes applied at a rate of 1 million per tree cost $15.00 per treated acre. This is approximately 33% more than the cost of chlorpyrifos, which once diluted to the finished spray concentration used in the field experiments costs $11.24 per treated acre. Barricade is available in concentrated form for $64 per gallon. Diluted to a concentration of 4% gel, the research team used approximately 5 gallons of undiluted gel per treated acre for a cost of $320 per acre to create a gel barrier with a 60cm radius at a depth of 1.5cm.
As can be seen above, relative to the equipment, chlorpyrifos, and nematode costs, the Barricade gel represents in absolute and per acre contexts the greatest expense for Peachtree borer suppression and would not be economically competitive with chlorpyrifos. However, it is important to note that the concentration of the Barricade gel (4%) and area covered could be modified to significantly reduce the cost with potentially little effect on efficacy. By reducing the concentration from 4% to 2% Barricade gel and reducing the treatment area from a 60cm radius to a 10cm radius covering just where the Peachtree borer is active, this would reduce the cost of Barricade from $320 to $4.44 per treated acre.
The final key expense considered is irrigation. As seen in the results from the field trials, the relative efficacy of nematodes in reducing infestation rates is significantly affected by irrigation. While well over half of the peaches grown in Georgia and other Southeastern states are irrigated, for producers without an irrigation system installing a new system represents a significant fixed cost. For farms without irrigation, installing a new drip irrigation (the most common system type in Georgia for orchard crops) can cost between $400 and $2,500 per acre depending upon a wide array of site and system factors. Assuming an intermediary cost of $1,000 per acre, installing an irrigation system, when viewed only through the lens of pest suppression as in this study, represents a significant cost. However, the returns to irrigation in revenue generation through increased and improved fruit production (which is not considered here), are significant. For orchards with an irrigation system already installed, the cost of seven irrigation events over a two week time span is assumed to range between $5 and $15 per acre depending upon location, equipment, water source, and water needs. However, since the water applied is an expense that would occur regardless of whether nematodes were applied, the assumed cost of applying nematodes with and without irrigation is the same, $15 per treated acre.
Combining all of the cost information, the per acre cost (ignoring equipment costs) of treating with chlorpyrifos is $11.24, nematodes without irrigation is $15, nematodes with irrigation is $15, and nematodes with Barricade is between $19.44 and $345. Based upon the cost estimates, chlorpyrifos is the lowest cost option followed by nematodes with or without irrigation. However, due to the low success rate of suppressing the infestation rate of Peachtree borer by nematodes without irrigation, this strategy does not appear to be an attractive alternative to chlorpyrifos. Nematodes applied with Barricade delivered superior reductions in infestation rates to nematodes applied with irrigation in the current trials. However, previous experiments (e.g., Cottrell and Shapiro-Ilan, 2006; Shapiro-Ilan et al. 2009, 2015) found that nematodes with irrigation performed on par with chlorpyrifos. Given the similar low-end cost estimates of these two methods, two results emerge. First, for growers without irrigation systems, Barricade could to be an economically viable option if it maintains its efficacy at lower concentration levels. Second, for growers with irrigation systems, due to the similar efficacy of nematodes in previous experiments compared to chlorpyrifos, nematodes applied with irrigation offers a marginally more expensive alternative to chemical insecticides. Not considering the cost of irrigation, which for irrigated orchards does not represent an additional cost beyond normal watering activities, application of nematodes ($15) is about 33% more expensive per treated acre than chlorpyrifos ($11.24).
Overall, combining the cost data and field trial data, several conclusions emerge. First, for growers who adopt nematodes for peachtree borer suppression, there does not appear to be a justification to purchase an alternative applicator if a watering can, handgun, or boom sprayer is already owned (as is among most growers). Second, on a pure cost-basis, chlorpyrifos is the superior alternative for reducing infestation rates followed by nematodes applied without irrigation. When contrasting the relative efficacy of the different treatments with their per acre costs, chlorpyrifos remains the most effective lowest cost alternative followed by the low-end cost estimates of nematodes with Barricade and nematodes with irrigation (assuming an irrigation system is already installed). While slightly more expensive than chemical insecticides, it is important to note that other advantages of nematodes exist that are not captured in the cost analysis. With growing regulatory pressure and environmental concerns surrounding the use of farm chemicals, the results of this study indicate that nematodes with irrigation or with Barricade on non-irrigated orchards have the potential to be economically viable alternatives. However, for non-irrigated orchards, given that the cost of the Barricade gel represents a significant component of this strategy of deploying nematodes, future research exploring the efficacy of reduced Barricade concentrations and smaller application areas should be explored.
Farmer Adoption
On a small scale the use of entomopathogenic nematodes for use against peachtree borer has been increasing. The largest commercial nematode producer that sells product in the US has changed their recommendations for control of this pest based on our research results. We expect that grower adoption will continue and there is significant potential for larger operations to also consider the approach.
Areas needing additional study
- Additional demonstration trials
- Additional talks at grower meetings (such as the planned talk at the Southeastern Fruit and Vegetable Conference January 2016) will also lead to great dissemination.
- Additional research to refine and improve the biocontrol approach is needed including further optimization of timing and longer-term comparisons of biocontrol applications relative to other tactics.
- Additional research to determine the feasibility of timing and or modifying borer applications to target other important pests, e.g., plum curculio, root weevils, when present, that are also suppressed by nematode treatments in the soil.
This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through the Southern Sustainable Agriculture Research and Education program under subaward number LS11-241. USDA is an equal opportunity employer and service provider.