Effects of commercial pesticides on the nematode biological control agent Pochonia chlamydosporia

Abstract

ABSTRACT Tomato Solanum lycopersicum plants are exposed to a wide range of pests and diseases in protected cultivation, including root-knot nematodes (RKN), Meloidogyne spp. As the application of chemical nematicides is progressively being restricted in the EU, biological control agents such as Pochonia chlamydosporia are being considered as sustainable alternatives. Nevertheless, success in the control of RKN depends on the compatibility of the fungus with pesticides used to manage other pests and diseases. We tested the in vitro acute and chronic effects of twelve different commercial pesticides used throughout a tomato cropping cycle on P. chlamydosporia. All pesticides significantly inhibited radial growth of the fungus at 22 days, with exception of methiocarb (Mesurol 200), spiromesifen (Oberon), copper-metalaxyl-M (Ridomil Gold R) and oxamyl (Vydate 10L). All fungicides produced significant acute and chronic negative effects on chlamydospore viability. Insecticides methiocarb, spinosad (Spintor) and indoxacarb (Steward) did not affect chlamydospore germination at the tested concentration of active substance (100 mg·L−1) of pesticide in the acute effects test, but all tested pesticides significantly reduced chlamydospore viability in the chronic 6-week-exposure test. Importantly, chlamydospore germination rates recorded were higher in the 12-week than in the 6-week-exposure chronic test, hinting at P. chlamydosporia acclimation or recovery. In view of differences in compatibility of commercial pesticides with P. chlamydosporia, acting on different fungal life stages in acute and chronic processes, these must be carefully selected and the timing of their application considered in the design of crop protection strategies against RKN to improve the biological control success.