The compatibility of the fungicide azoxystrobin with Pochonia chlamydosporia, a biological control agent for potato cyst nematodes (Globodera spp.)

The biological control potential of Pochonia chlamydosporia against root-knot ( Meloidogyne spp.) and cyst-forming ( Heterodera and Globodera spp.) nematodes is widely appreciated. In spite of this, little has been undertaken to determine the compatibility of this fungus with modern fungicides. A series of experiments were undertaken to investigate the effect of azoxystrobin on P. chlamydosporia . Initial Petri dish experiments found a significant reduction in the growth of P. chlamydosporia . EC₅₀ values were calculated at 7 and 14 mg L⁻¹, respectively, for hyphal growth and chlamydospore germination. A microcosm experiment based on counts of the colony-forming units of the re-isolated fungus showed a reduction in EC₅₀ values for azoxystrobin in soil after 12, 20 and 40 days incubation (1.25, 1.00 and 3.00 mg kg⁻¹ soil, respectively). There was evidence the fungus recovered over time in response to azoxystrobin application. This was also demonstrated in a glasshouse experiment where EC₅₀ values of 1.32 and 4.4 mg kg⁻¹ soil were obtained for 35 and 49 days after planting (DAP), respectively.