Enhancing Natural Enemy Systems: Biocontrol Implementation for Peachtree Borers

Enhancing Natural Enemy Systems: Biocontrol Implementation for Peachtree Borers

Summary

Our overall goal is to tackle the primary remaining challenges to implementing entomopathogenic nematodes as a biocontrol tactic for borer pests, and to assess the broader impact of this biocontrol strategy on the system. Since our last report we have made substantial progress by 1) Evaluating a full set of field experiments to determine optimum irrigation level and method of applying entomopathogenic nematodes for control of peachtree borer, and 2) screening formulations for ability to protect nematodes from UV radiation and desiccation, 3) Test new nematode formulation levels in the field for control of lesser peachtree borer. Results indicated that beneficial nematodes (Steinernema carpocapsae) caused high levels of peachtree borer suppression; irrigation is required to achieve efficacy, but when barricade was applied to substitute for irrigation a statistically similar level of suppression was observed compared with standard chemical insecticide treatments, 2) A reduced rate of Barricade firegel can be used in conjunction with beneficial nematodes to control lesser peachtree borer. These field tests will need to be repeated. We are on task to achieve our objectives with the end-product being development of a sustainable system for borer control.

Our overall goal is to tackle the primary remaining challenges to implementing entomopathogenic nematodes as a biocontrol tactic for borer pests, and to assess the broader impact of this biocontrol strategy on the system. Since our last report we have made substantial progress by 1) Evaluating a full set of field experiments to determine optimum irrigation level and method of applying entomopathogenic nematodes for control of peachtree borer, and 2) screening formulations for ability to protect nematodes from UV radiation and desiccation, 3) Test new nematode formulation levels in the field for control of lesser peachtree borer. Results indicated that beneficial nematodes (Steinernema carpocapsae) caused high levels of peachtree borer suppression; irrigation is required to achieve efficacy, but when barricade was applied to substitute for irrigation a statistically similar level of suppression was observed compared with standard chemical insecticide treatments, 2) A reduced rate of Barricade firegel can be used in conjunction with beneficial nematodes to control lesser peachtree borer. These field tests will need to be repeated. We are on task to achieve our objectives with the end-product being development of a sustainable system for borer control.

Objectives/Performance Targets

Objective I) To determine the optimum method of applying entomopathogenic nematodes (EPNs) for control of peachtree borer (PTB) on a commercial scale.

Objective II) Determine the optimum entomopathogenic nematode formulation for control of lesser peachtree borer (LPTB).

Accomplishments/Milestones

Objective I) To determine the optimum method of applying entomopathogenic nematodes (EPNs) for control of peachtree borer (PTB) on a commercial scale.

The primary goal is to determine the optimum method of application for EPN control of peachtree borer (Synanthedon exitiosa) (PTB); levels of irrigation associated with EPN application will also be tested.

Two field experiments to address Objective 1 were initiated.

I. One experiment was initiated on Lane’s Peach Orchard, Fort Valley, GA. The other test was initiated in Byron, GA on the USDA-ARS research station. The experiment at Lane’s orchard addresses irrigation requirements, whereas the experiment in Byron addresses the method of application. The nematode used in all experiments was Steinernema carpocapsae. The application rate was 1.5 million nematodes per tree.

On Lane’s orchard we applied the following treatments: 1) Nematodes without irrigation, 2) Nematodes with 3 irrigation events per wk, 3) Nematodes without irrigation but with gel applied to protect against desiccation, 4) Lorsban (standard chemical insecticide). There were 4 trees per plot, and each treatment was replicated four times.

Results confirmed that S. carpocapsae can cause high levels of peachtree borer mortality but we discovered that irrigation is needed for nematodes to achieve efficacy (Fig. 1). However, when barricade was applied to substitute for irrigation a statistically similar level of suppression was observed compared with standard chemical insecticide treatments

II. At Byron station the following treatments were applied: 1) Nematodes applied by boom sprayer, 2) nematodes applied by handgun, 3) nematodes applied by trunk sprayer, 4) Lorsban, 5) non-treated control, 6) repeated handgun spray but using a different nematode product, 7) in-vivo grown nematodes applied with a watering can (positive control). There were 7 trees per plot and each treatment was replicated three times.

Results indicated that the population was highly variable and unfortunately no statistical difference were detected (even between the standard chemical insecticide and untreated control) (Fig. 2).

Objective II) Determine the optimum entomopathogenic nematode formulation for control of lesser peachtree borer, Synanthedon pictipes (LPTB):

In previous studies we discovered that the firegel, Barricade” can protect nematodes (e.g., S. carpocapsae) from harmful UV radiation and desiccation. One problem with using Barricade could be that the high concentration of gel does not go through a grower’s normal spray equipment and thus the grower would have to do to sprays (one for nematodes followed by a Barricade spray); this could be seen as cumbersome. Therefore, we investigated whether a reduced concentration of Barricade gel could be implemented to go through the sprayer (with the nematodes) but still protect the nematodes from harmful environmental conditions. First, Barricade at 0, 0.5, 0.1 and 2% was tested with nematodes in a Petri dish experiment conducted in full sun. Exposure of treatments to the insect, Galleria mellonella (used as a model host) over time was used to determine the longevity of treatment effects. An untreated control (no nematodes) was also included. This experiment indicated that 2% Barricade or less can provide protection to nematodes (Fig. 3). Note, 2% Barricade can go through spray systems (whereas the full Barricade rate, 4% cannot).

Following up on the above experiment, a field test was implemented to determine the efficacy of 2% Barricade plus nematodes in controlling lesser peachtree borer. Nematodes were applied with full-rate and 2% Barricade or with no Barricade. An untreated control and standard chemical (lorsban) was also included. Results indicated that Nematodes + Barricade at full and 2% rates provided control equal to Nufos (Lorsban); nematodes without a protective formula failed to control the pest (Fig. 4).

Future research will entail repeating the field experiments indicated above and also conducting a system level economic analysis.

• LS11-241 Figures

Impacts and Contributions/Outcomes

Based on our progress we have shown great potential for control of borers using an environmentally friendly approach. The results thus far have been presented at one professional and one grower meeting. We anticipate that our novel findings will facilitate the adoption of a sustainable biocontrol solution for peachtree borer control in peaches. The results will also be applicable to other cropping systems.

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