No abstract

The objective of this work was to quantify the reduction of soybean grain yield caused by Tetranychus urticae damage, and to propose an economic injury level (EIL) for this pest in the crop. The experimental design was set up in randomized complete blocks, with four replicates and a 4x2 factorial arrangement with four levels of mite infestation, with or without mite control. Chlorotic symptoms were evaluated using a damage scale of 1 to 4. Soybean grain yield, number of pods, number of grains, and 1,000-grain weight were quantified for each segment of plant canopy (lower, middle, and upper) and for the whole plants. The chlorophyll content in the leaves was evaluated using the SPAD index. The population density of one two-spotted spider mite per cm2 of leaf area caused the following reductions: one pod per plant, two grains per plant, 0.7 g of 1,000-grain weight, and 0.35 g of grain yield per plant or 42 kg ha-1. Based on the equation y = 4,369 - 41.99x, the EIL of one two-spotted spider mite per cm2 is determined by considering a control cost of US$ 20.00 ha-1 and a soybean crop value of US$ 350.00 Mg-1. As to chlorotic symptoms, the EIL is set between damage scores 1 (no apparent mite damage) and 2 (yellow mottling beginning to appear).

Stink bugs and whiteflies are major concerns for pest management in Brazilian soybean fields, causing severe economic losses to soybean growers and leading to excessive insecticide applications per crop cycle. Despite biological differences, these two sap-sucking pests often co-occur in soybean fields and can be successfully managed with the same insecticide spray, reducing operational costs to the growers. The aim of this work was to evaluate the efficacy of eleven insecticides in the control of stink bugs and whiteflies. Two insecticide sprays were made with an interval of 14 days between them. The results from ANOVA and Tukey post-hoc test (P≤0.05) revealed significant differences among treatments. Acetamiprid + bifenthrin (75 + 75 g a.i. ha-1) was the most efficient treatment for the control of stink bugs, reaching 97.8% of insect mortality. Cyantraniliprole + bifenthrin (50 + 50 g a.i. ha-1) was the most efficient treatment for the control of whiteflies, reaching 78.8% of insect mortality. This treatment also presented the highest combined control of stink bugs and whiteflies, reaching 83.5% of insect mortality