SUBSTITUIÇÃO DO ACEFATO POR ISOXAZOLINA + PIRETRÓIDE EM UM MANEJO QUÍMICO ROTACIONADO CONTRA Dalbulus maidis, COM CONSEQUÊNCIAS FITOSSANITÁRIAS E PRODUTIVAS, PARA MILHO SAFRINHA

Abstract

The corn leafhopper, Dalbulus maidis (DeLong & Wolcott) (Hemiptera: Cicadellidae), the vector of the corn stunt disease complex, is among the principal constraints to maize production in Brazil, demanding integrated management programs that rotate insecticidal modes of action (MoA). However, experimental comparisons that explicitly connect spray programs to maize phenology while contrasting distinct MoA remain scarce. We evaluated, in the hybrid MG540 grown under rainfed second-season conditions, the agronomic relevance of two sequential foliar spray programs on vector populations, stunt incidence, and grain yield. The trial followed a randomized complete block design with three treatments (T). T1 was an absolute, water-only control. T2 comprised thiamethoxam + lambda-cyhalothrin at VE, three sequential applications of isocycloseram + lambda-cyhalothrin at 5-7 day intervals, one application of profenofos + cypermethrin, and two applications of acetamiprid + lambda-cyhalothrin (at 14-day intervals). T3 followed the same calendar as T2, but replaced isocycloseram + lambda-cyhalothrin with acephate in the three central sprays. Throughout vegetative development, we periodically monitored (per 1 m row) the number of leafhoppers per plant, the percentage of plants with leafhoppers, and the percentage of plants showing stunt symptoms. These metrics were paired with control efficacy (EC%) corrected by the Henderson–Tilton method. At the end of the phenological cycle, grain yield (sacks ha⁻¹; 60-kg sacks) was estimated for each treatment. Both time (spray calendar) and treatment effects were significant for all periodic parameters and their corresponding EC%. T2 sustained more stable suppression during the intermediate window, with a peak around 5-7 days after application of the fourth spray (5-7 DAA4), whereas T3 produced a stronger initial knock-down effect followed by mid-cycle instability. Stunt incidence emerged late, with the hierarchy T1 > T2 > T3, and higher early-outbreak efficacy under T2. For yield, T2 reached 161.19 ± 19.00 sacks ha⁻¹, T3 achieved 138.00 ± 18.00 sacks ha⁻¹, and T1 only 92.00 ± 22.00 sacks ha⁻¹. Overall, the application program embodied by T2 combined consistent vector suppression, mitigation of stunt expression, and high yield. Intensive monitoring from VE to V4, rotation of MoA with substitution toward newer insecticides, and reapplications scheduled between 5-7 days after the third to fifth applications (5-7 DAA3 and 5-7 DAA5) emerge as actionable findings to help growers manage high D. maidis pressure more decisively, protectively, and productively under field conditions.