Association between chemical properties of vineyard soils and occurrence of entomopathogenic fungi causing different levels of mortality in Planococcus ficus

Abstract

Global demand for environmentally friendly grapevine cultivation and pest control has necessitated an improved understanding of the relationship between soil properties and beneficial, naturally occurring antagonists such as entomopathogenic fungi (EPF). Sixty six soil samples were collected from 22 vineyards in the Western Cape, South Africa. The association between soil nutrient status and EPF prevalence was examined. Fungi were isolated with methods of insect baiting and selective media. In addition, fungal isolates were tested against a key grapevine pest, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae). Pathogenicity of fungal strains against P. ficus was assessed with an immersion bioassay at a concentration of 1 × 108 conidia ml–1. Twenty-three fungal strains were isolated and correspondence analysis of data indicated a positive association between EPF (Metarhizium robertsii (Hypocreales: Clavicipitaceae) and Clonostachys rosea f. catenulata [Hypocreales: Bionectriaceae]) occurrence and optimum to high levels of soil-based macronutrients (C, N and Ca). Logistic regression revealed that K was positively correlated with M. robertsii (estimate = 0.03 ± 0.01; P < 0.05; odds ratio = 1.03). Strains of Beauvaria bassiana (Hypocreales: Cordycipitaceae) caused the highest mortalities (77.0 ± 2.0% to 87.0 ± 3.0%). This study showed that some soil nutrient properties corresponded to greater occurrence of EPF in grapevine soils.