Influence of herbicides on the efficacy of biological nematicides Pochonia chlamydosporia and Bacillus firmus for the management of Meloidogyne javanica in a Urochloa brizantha–soybean succession system

Abstract The use of biological nematicides has expanded significantly in recent years, becoming an important component of integrated nematode management. However, their compatibility with herbicides commonly used in agricultural systems remains poorly understood. This study evaluated the potential interference of pre-emergent herbicides on the efficacy of the biological nematicides Pochonia chlamydosporia and Bacillus firmus for the management of Meloidogyne javanica in a Urochloa brizantha– soybean succession system under greenhouse conditions. The experiment was conducted in a completely randomized design with eight replicates, arranged in a factorial scheme (4 × 2 × 3), corresponding to nematicide strategy, brachiaria management method (mechanical or chemical), and herbicide treatment (imazethapyr, S-metolachlor, or no herbicide). Treatments were established in 1.8-L pots containing a soil:sand mixture (1:3) and planted with a single U. brizantha cv. Marandu plant. Nematicide treatments consisted of no application or seed treatment with Rizotec® (200 g per 100 kg of seed) or Votivo Prime® (100 mL per 100 kg of seed). Plants were inoculated with 1000 M . javanica eggs and second-stage juveniles. After 90 days, plants were either manually cut or chemically desiccated with glyphosate (Xeque-Mate®, 2480 g a.i. ha⁻ 1 + Assist®, 0.5% v/v). Pots were maintained fallow for 30 days prior to soybean sowing (three seeds per pot, treated with Rizotec® or Votivo Prime®). Pre-emergent herbicides imazethapyr (Vezir®, 106 g a.i. ha⁻ 1 ) or S-metolachlor (Dual Gold®, 1440 g a.i. ha⁻ 1 ) were applied, along with a non-treated control. The total nematode population was assessed at 75 days after soybean emergence. Data were subjected to analysis of variance, and means were compared using the Scott–Knott test at a 5% significance level. Under mechanical management of U. brizantha , the application of B. firmus only to soybean resulted in higher M. javanica populations compared to chemical management. The application of S-metolachlor reduced nematode populations when P. chlamydosporia was applied to both crops and when B. firmus was applied only to soybean. Overall, imazethapyr and S-metolachlor did not negatively affect the efficacy of P. chlamydosporia and B. firmus for the management of M. javanica under the conditions evaluated.