Efficacy of Steinernema carpocapsae plus fire gel applied as a single spray for control of the lesser peachtree borer, Synanthedon pictipes

Abstract

The efficacy of aboveground applications of entomopathogenic nematodes (Heterorhabditis spp. and Steinernema spp.) can be severely limited by the nematode’s susceptibility to UV radiation and desiccation. The lesser peachtree borer, Synanthedon pictipes, is a major pest of stone fruit; larvae attack trees aboveground by tunneling into the trunk and scaffold limbs. In previous research, Steinernema carpocapsae, caused high levels of S. pictipes mortality when a sprayable fire gel (Barricade®) was applied on top of the nematode application as a protectant. One drawback to the approach is that two applications must be made (first nematodes are applied followed by the fire gel); furthermore, the previous experiments did not compare nematode application to the existing standard chemical insecticide. Therefore, the objectives of this study were to (1) determine if a diluted rate of fire gel can protect nematodes when applied as a single spray, and (2) compare the efficacy of nematode applications with the chemical insecticide, chlorpyrifos. The experiment was conducted in a peach orchard in Quincy, Florida in 2013 and 2014. Treatments included: (1) chlorpyrifos, (2) S. carpocapsae applied in aqueous suspension only or (3) with a full rate (approximately 4% applied separately) or (4) 2% Barricade® (applied with nematodes in a single spray), and (5) a non-treated control. The treatments were applied post-harvest (in the fall) to S. pictipes-infested bark wounds; S. pictipes survival was assessed 8 (2013) or 14 (2014) d post-application. In 2013, chlorpyrifos and nematodes with Barricade® at 2% or the full rate reduced S. pictipes survival relative to the non-treated control and nematodes without Barricade®. In 2014, nematodes applied with 2% Barricade® was the only treatment that reduced S. pictipes survival. We conclude that S. carpocapsae and Barricade® can be applied as a single spray, and in our experiments the treatment was at least as effective as the chemical standard.