Efeito residual e tempo de exposição à abamectina em Aceria guerreronis Keifer: implicações do uso de adjuvantes em campo

Abstract

Controlling Aceria guerreronis Keifer in coconut crops is a challenge for producers, as the growth of colonies on bracts protects them from contact with acaricides. Therefore, control depends on the contamination of mites during their dispersal by the residual effect of applied products, and the addition of adjuvants can improve this effect, even prolonging it. This study aimed to determine the contamination time of the commercial product VERTIMEC® 18 EC (Abamectin) on A. guerreronis to cause mortality and to evaluate the effect of adding adjuvants on its residual time in the field. For the bioassay for exposure time and mortality in the laboratory, experimental arenas with leaflet fragments (2x4 cm) were immersed in VERTIMEC® 18 EC (300 ml/ha) and control (distilled water) treatments, and left to dry exposed to air for 20 minutes. Then, 30 larger A. guerreronis individuals were transferred and exposed to waste for 15 min, 30 min, 60 min, and 120 minutes. After each time point, the mites were transferred to a new experimental arena with a fragment without product, and mortality was evaluated after 12 hours. For the residual time bioassay in the field, 4 plants were sprayed with the following treatments: Negative control (water only), Positive control (VERTIMEC® 18 EC (300 ml/ha)), VERTIMEC® 18 EC + Silwet 0.25% v/v, and VERTIMEC® 18 EC + Speed ​​Oil 0.25% v/v. Leaflets were collected at 24h, 72h, and 144h after spraying to set up the experimental units. Thirty of the largest A. guerreronis individuals were transferred, and mortality was assessed after 12h. For the contamination time bioassay, the mortality rate differed significantly between treatments (χ² = 82.33; df = 4; p < 0.001), with the 120-minute treatment showing significantly higher mortality than all others. For the field bioassay, the Vertimec and Vertimec + Speed ​​Oil treatments, 144 h after application, showed a significant difference in mortality (χ² = 16.50; df = 2; p < 0.001), where the VERTIMEC® 18 EC treatment showed significantly higher mortality than the control (p = 0.005), while VERTIMEC® 18 EC + Speed ​​Oil did not differ from the control (p = 0.447). For the VERTIMEC® 18 EC + Silwet AG treatment, the mortality rate differed significantly between treatments 24 h after the interval (χ² = 28.34; df = 1; p < 0.001), showing significantly higher mortality compared to the control, a result corroborated by the Wilcoxon rank-sum test (W = 34.5; p < 0.001). However, 72 hours after the date, no statistically significant difference was detected in the mortality rate between the control (χ² = 3.68; df = 1; p = 0.055). Abiotic factors such as rainfall can influence the persistence of products with different bases in ways that are not yet fully understood, especially when they occur less than 24 hours after the explosion, weakening the efficiency of the applications. However, more studies are needed to understand how the interaction between the spray solutions and these factors occurs, so that strategies can be developed to mitigate it .