Assessing the threat of the Polyphagous Shot Hole Borer beetle (PSHB, Euwallacea fornicatus) and its symbiotic fungus (Fusarium euwallaceae) to deciduous fruit trees in the Western Cape Province of South Africa

We assessed the threat of PSHB and its fungal symbiont to deciduous fruit trees. We determined the susceptibility of selected fruit trees to F. euwallaceae and the effects of branch diameter, cultivar and number of inoculation points on the susceptibility of hosts.

Branches of fruit trees in orchards were inoculated with isolates of F. euwallaceae obtained from fruit trees in garden settings. Fungal growth rates (and survival) were determined from inoculated wood after allowing the fungus to grow for at least three months.

Pathogenicity of the fungus was confirmed in apple, plum cv. Angelino, Fortuner and ‘Sungold’, and nectarine. Number of inoculation points and branch size had no influence on fungal growth rates. No differences in cultivar susceptibility was detected. PSHB was able to breed in various Prunus species and apple.

Similar to Almonds in California we confirm the pathogenicity of F. euwallaceae on plum, nectarine, and apple trees and the ability of the beetle to breed in many Prunus species and apple. The risk of successful beetle infestation and production losses is therefore high in these hosts.

PSHB and its pathogenic fungus is a serious potential threat to deciduous fruit production.