Cytospora Canker and the Establishment of Lesser Peachtree Borer (Lepidoptera: Sesiidae) in Peach Trees

Abstract

Susceptibility of peach tree wounds infected with Cytospora canker to invasion by lesser peachtree borer (LPTB), Synanthedon pictipes (Grote & Robinson), was investigated. Treatments were 1) impact wounds on the scaffold limbs, 2) impact wounds treated with 1% naphthalene acetic acid (NAA) to induce gumming, and 3) impact wounds infected with Cytospora canker. Each treatment was made at three different times during spring 1983. Both date wounds were made and wound treatment had a significant effect on number of wounds becoming infested with LPTB. Wounds made in early April were less susceptible to infestation by borers than wounds made in late May; wounds made in late April were intermediate in susceptibility. Wounds infected with Cytospora at the beginning of the experiment were infested with LPTB earlier and to a greater extent than either untreated wounds or wounds treated with NAA. As the experiment progressed. many of the untreated or NAA-treated wounds that did not heal became infected with Cytospora, after which 35–38% of them were invaded by LPTB. In only one instance did a wound become infested with borers before its infection with Cytospora; otherwise, establishment of borers either followed or, in a few cases, coincided with infection of wounds with the disease. Relationship of structure of Cytospora-infected wounds to LPTB egg deposition and larval entry is discussed. On smooth-barked, otherwise healthy peach trees, such as those used in this experiment, infection of wounds by Cytospora is important to the establishment and spread of LPTB infestations in peach orchards.