Control of the Peachtree Borer Using Beneficial Nematodes

Credit:

David I. Shapiro-Ilan & Ted E. Cottrell, USDA-ARS, Southeastern Fruit and Tree Nut Research Laboratory, Byron, GA
Russell F. Mizell III, Department of Entomology, NFREC, University of Florida, Quincy, FL
Mercy A. Olmstead, Horticultural Sciences Department, UF/IFAS, University of Florida, Gainesville, FL

The peachtree borer, Synanthedon exitiosa, is a major pest of peaches and other stone fruits. Our research indicates that entomopathogenic nematodes, also known as beneficial nematodes, can be used effectively to control the insect. Beneficial nematodes are safe and natural bio-insecticides. They’re produced commercially by several companies, and are used to control a variety of economically important insect pests such as the black vine weevil, diaprepres (diaprepes… not sure which spelling is correct – LB) root weevil, fungus gnats, and various white grubs.

Unlike harmful plant-parasitic nematodes, beneficial nematodes only attack insects. The nematodes enter insects’ bodies through natural openings or sometimes directly through the insect’s cuticle. The insect dies, usually within 24 to 48 hours.  The nematodes reproduce within the body, after which the offspring exit the corpse to find new insects to attack.

Current peachtree borer management across the southeastern US relies solely upon preventative post-harvest chemical control, particularly, chlorpyrifos. Due to environmental and regulatory concerns, research toward developing alternative pest control measures is warranted.

We conducted an experiment to determine beneficial nematode efficacy in controlling peachtree borer in a preventative manner with summer/fall applications. This follows the same approach commonly used by growers to manage peachtree borer; insecticides are sprayed in the later summer or fall to prevent damage to the tree. For nematode application, we compared common equipment that commercial growers could use for nematode application including a boom sprayer, trunk sprayer and handgun. Treatment applications were made in two consecutive years, September 2012 and September 2013. Results were combined for both years. All nematode treatments and chlorpyrifos reduced peachtree borer infestation relative to the non-treated control; there was no difference between chlorpyrifos and the nematode treatments.

We also measure the efficacy of the beneficial nematode as a curative control for existing infestations of peachtree borer, as missed applications, poor application timing or other factors may result in high levels of peachtree borer infestation through the following spring. Prior to our research, curative control did not exist. The effects of treatment on infected trees were assessed 3-6 weeks later by determining the number of surviving peachtree borer larvae per tree. All nematode treatments provided significant curative control; in contrast, chlorpyrifos failed to significantly reduce the number of surviving larvae.

The nematodes can be applied using standard agricultural equipment. It is important to keep the soil moist for at least two weeks after applying nematodes. Alternatively, if irrigation does not exist in the orchard, a gel can be applied to the soil surface to keep the nematodes moist.

Our research concluded that the beneficial nematode, Steinernema carpocapsae, can be applied effectively for control of peachtree borer.  Applications can be made preventatively in the summer/fall or curatively in the spring. Nematode efficacy is similar to chlorpyrifos in preventative applications and superior in fall applications, offering farmers an alternative to traditional pest treatments.

CAPTIONS

Fig 1: Hatched larvae of the peachtree borer, Synanthedon exitiosa, bore into the trunk near the soil surface and tunnel into the roots. Photo by Stacy Byrd, USDA-ARS

fig 2: Beneficial nematodes, genera Steinernema and Heterorhabditis, are safe and natural bio-insecticides. Photo by J. Morales-Ramos, USDA-ARS

fig 3: Chart: percentage peachtree borer infestation following preventative applications of beneficial nematodes (N) via boom sprayer, handgun or trunk sprayer. Chlorpyrifos and a non-treated control were included for comparison.

Fig 4: Chart: Percentage peachtree borer infestation following curative applications of beneficial nematodes (N) via boom sprayer, handgun or trunk sprayer. Chlorpyrifos and a non-treated control were included for comparison.