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 second full set of field experiments to determine optimum irrigation level and method of applying entomopathogenic nematodes for control of peachtree borer, and 2) Completing the second trial for 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. Also, against both pests (peachtree borer and lesser peachtree borer), the beneficial nematode treatments were able to cause equal levels of control compared with the standard chemical insecticides. Next we will explore further curative nematode applications for peachtree borers and assess large grower demonstrations. 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 implemented; both of these experiments were repeats (second field trials) following on trial 1 that was conducted the previous year. Two years of field data are generally always desired for experiments to ensure scientific validity and thus these experiments are now completed.

1. Both experiments were implemented in Byron, GA on the USDA-ARS research station (previous trial for one experiment used commercial orchards but the farmers sprayed prior to our experiment this past year). The first experiment addressed irrigation requirements, whereas the experiment second addressed the method of application. The nematode used in all experiments was Steinernema carpocapsae. The application rate was 1.5 million nematodes per tree.

In the first experiment 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.

Similar to the previous year, 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. Nematodes applied with irrigation also caused similar levels of control compared to the chemical insecticide (Fig. 1).

1. In the second experiment 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.

Data s from the trials conducted in 2013 and 2014 were combined for analysis. Results indicated that all methods of nematode application suppressed infestation below the non-treated control and were similar to chlorpyrifos, except handgun treatment was intermediate (Fig. 2).

Thus, our results indicate that nematodes can be applied to control peachtree borer with similar efficacy compared to chemical insecticides, and irrigation or Barricade gel can be used to apply the nematodes with various standard spray equipment.

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 two 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. Note, 2% Barricade can go through spray systems (whereas the full Barricade rate, about 4% cannot).

Following up on the above experiment, field test were 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. In the past year the second field trial was conducted. Surprisingly, results from the second trial indicated that the Nematodes + Barricade at 2% was the only treatment that suppressed lesser peachtree borer below levels observed in the non-treated control; the treatments (including the chemical standard) were not different from each other (Fig. 3). Thus, nematodes plus Barricade at 2% can be applied effectively in a single spray to control lesser peachtree borer.

Future research will entail repeating a field experiment that tested a curative ability of nematodes to control peachtree borer with a spring application (usually applications are made in the fall); the first year results showed excellent results with nematodes out-performing the chemical standard. Also, we have initiated large grower demonstration trials and these will be assessed later in April and May 2015. Lastly, a system level economic analysis will be conducted.

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Impacts and Contributions/Outcomes

Based on our progress we have shown great potential for control of borers using an environmentally friendly approach. During this past year only (since our last report), results have been presented at two professional meetings and one grower meeting.

1. Shapiro-Ilan, Cottrell, Mizell, & Horton: Suppression of Peachtree Borer and Lesser Peachtree Borer with Entomopathogenic Nematodes: Effects of Application Method and Formulation. Annual Meeting of the Entomolgoical Society of America. Portland, OR Nov 15-19 2014
2. Shapiro-Ilan, Cottrell, Mizell, & Horton: Enhancing the Efficacy of Entomopathogenic Nematodes for Control of Peachtree Borer and Lesser Peachtree Borer. Peach County Peach Update Meeting, Byron, GA. Feb 4, 2014.
3. Shapiro-Ilan, D. Improving Microbial Control Efficacy of Entomopathogenic Nematodes in Orchard Systems, International IPM Symposium, Salt Lake City, Utah, March 23-26, 2015.

We have also published one peer reviewed paper (more will be forthcoming):

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.

Finally, 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.

Collaborators: