Efeito residual de inseticidas aplicados via tratamento de sementes no controle de Dalbulus maidis

Abstract

The corn leafhopper, Dalbulus maidis (DeLong & Wolcott, 1923), is one of the most critical phytosanitary challenges in maize production, particularly due to its ability to transmit mollicutes and viruses associated with the maize stunt complex. The increase in its incidence is closely linked to intensified cropping systems, the persistence of volunteer plants, and the continuous availability of suitable hosts. In this context, seed treatment with systemic insecticides represents an important strategy to protect maize during the early growth stages, although the persistence of its protective effect remains poorly understood. This study evaluated the mortality of D. maidis on maize plants originating from seeds treated with thiamethoxam and thiamethoxam + lambda-cyhalothrin across three consecutive exposure periods, totaling twelve days of assessment. The experiment was conducted under greenhouse and laboratory conditions, using individual confinement cages, ten replicates per treatment, and periodic replacement of insects every 96 hours. Mortality was recorded at 24, 48, 72, and 96 hours within each period, and data were analyzed using generalized linear models with a binomial distribution, along with mortality correction. The results showed that both insecticides caused high mortality only during the first period, with reductions exceeding 45% after 72 and 96 hours, whereas no statistical differences from the control were observed in the subsequent periods. The sharp decline in mortality across later periods revealed the rapid reduction of residual activity, associated with plant physiological dynamics and inherent limitations of systemic insecticides. Thus, the limited persistence of these products highlights the need for complementary and well-planned management strategies, particularly in regions with a history of maize stunt diseases and reinforces the importance of understanding this temporal dynamic to support more precise agronomic decision-making and reduce the epidemiological risks associated with the corn leafhopper.