Fatores ambientais e tempo de degradação foliar de neonicotinóides no controle químico de insetos sugadores em soja

Abstract

The objective was to study the relationships between environmental conditions, the population of bedbugs and chemical control in different soy producing regions, as well as understanding the dynamics of swallowing and the effect of neonicotinoids applied with seed treatment on white fly nymphs. To study the effect of environmental conditions and chemical control in the population of bedbugs four trials were installed in four regions (Uberlândia-MG, Primavera do Leste-MT, Rondonópolis-MT and Santa Maria-RS) in randomized block design, containing 8 treatments: Control; Carbosulfan 400 SC (0,19 L ha-1); Carbosulfan 400 SC (0,23 L ha-1); Imidacloprid 700 WG (0,11 kg ha-1); Thiamethoxam 250 WG (0,17 kg ha-1); Bifentrin + Carbosulfan 200 CE (0,5 L ha-1); Imidacloprid + bifenthrin 250 SC (0,3 L ha-1) and Thiamethoxam + λ-cyhalothrin 247 SC (0,3 L ha-1) and 4 repetitions. We evaluated the number of bedbugs per meter in a soybean line at 0, 3, 7, 10 and 15 days after application (DAA) and collected the climatic data daily. To study the degradation and effect of neonicotinoids on white fly nymphs, a home vegetation trial was conducted to analyze the mortality of nymphs and field trials in Rio Paranaíba-MG and Lagoa Formosa-MG for two crops, where leaves were collected to analyze the concentrations of the products and count of nymphs at 0, 5, 15, 25, 35, 45 and 65 days after the emergence of soybean plants. In tests to understand the factors affecting the population of brown bedbugs, it was observed that insecticides presented different levels of interference in the population of E. heros according to the region, probably due to the effect of environmental conditions such as: relative humidity, temperature variation, maximum temperature and mainly rainfall. Insecticides provided a greater reduction in the population under conditions of population density close to the control level, which highlights the importance of monitoring crops to perform control measures. Under conditions of high population density, the insecticides bifentrin 50 + carbosulfan 150 EC, imidacloprid 250 + bifentrin 50 SC and imidaclorpid 700 WG provided greater population reduction. In trials assessing the degradation and effect of neonicotinoids on white fly nymphs, treatment of seeds with neonicotinoids thiamethoxam, imidacloprid and clothianidin was found, provided high mortality of white-fly nymphs in the greenhouse test, demonstrating the suitability of nymphs to these products. In field trials, thiamethoxam, imidacloprid and clothianidin, applied by seed treatment, showed a reduction in the number of nymphs in relation to the control in early plant development, but the density of nymphs per leaf increased throughout the cycle, due to degradation of the products. Despite the use of insecticides in seed treatment, crop monitoring should be performed frequently, from the beginning of the cycle, complementing the management with foliar applications, if necessary, aiming to keep the pest under control.