Normalmente, a aplicação de inseticidas para o controle de Anticarsia gemmatalis na cultura da soja é realizada com bicos hidráulicos. Dentre outras possibilidades se destacam a assistência de ar junto à barra de pulverização e a aplicação de baixo volume oleoso por atomizadores rotativos de discos. Em um experimento realizado na cultura da soja, na safra 2009/10, avaliou-se a eficiência de controle de A. gemmatalis utilizando-se sistemas de aplicação e inseticidas. O delineamento utilizado foi bifatorial com o fator A constituído por sistemas de aplicação, sendo: A1 - pulverização com atomizadores rotativos de discos; A2 - pulverização com bicos hidráulicos; A3 - pulverização com assistência de ar e o fator D, constituído por inseticidas, sendo: D1 - Cipermetrina e D2 - Lufenurom + profenofós. Não houve interação do inseticida com o sistema de aplicação; além disso, a mistura de inseticidas Lufenurom + Profenofós apresentou efeito residual superior a Cipermetrina. O sistema de aplicação baixo volume oleoso com atomizadores rotativos de discos e o sistema de bicos hidráulicos com assistência de ar junto à barra de pulverização são mais eficientes que a pulverização com bicos hidráulicos no controle de Anticarsia gemmatalis na cultura da soja.

The population fluctuations of spider mites on different soybean cultivars were studied in two experiments performed in the municipalities of São Sepé (experiment 1) and Santa Maria (experiment 2) in the state of Rio Grande do Sul, Brazil. The number of cultivars was 20 in São Sepé and 25 in Santa Maria, and at each location leaves were sampled from 15 plants per cultivar every week throughout the entire plant developmental cycle, amounting to 11 and 10 samplings in experiment 1 and 2, respectively. The statistical analysis revealed that mite densities varied significantly with cultivar and time. Besides, the interaction between soybean cultivars and sampling times was significant at both locations. This indicates that the populations did not vary in the same way among cultivars over time, which is attributed to differences among the cultivars with respect to their phenology and response to spider mites. Equations for describing the mite population dynamics were estimated for each cultivar, mostly by fitting cubic equations to the weekly growth rates (per capita changes) in mite densities. We also found that the highest growth rates for mites on soybean cultivars in both locations occurred after the beginning of flowering, when the plants shifted from the vegetative to reproductive stages, about 3 weeks before reaching the peak densities.

To control phytophagous mites on soybean crops in an economically viable way, it is necessary to quantify the occurrence of the mites on the leaflets. Estimating the number of mites cm(-2) on leaflets is more difficult because of their irregular distribution on the leaflet surface. Therefore, the aim of this study was to determine the count-area/leaflet and the number of soybean leaflets to quantify the mites. One hundred infested plants were randomly collected. One leaflet was removed from each plant and divided into 32 sections (1.0 cm(2) per section), arranged in four columns and eight rows, to count the mites (adults, nymphs and eggs). The ideal count-area size per leaflet (Xo) was estimated by the maximum curvature of the coefficient of variation method for each of the 100 leaflets. For a count-area of Xo size, we obtained the number of mites cm(-2) per leaflet and, using the bootstrap resampling method, we estimated the point and interval averages as well as the sample size for a pre-established error. We suggest that the determination of the evaluated area size on each soybean leaflet (20 cm(2) in this case) and the bootstrap resampling estimate of the appropriate number of leaflets (12 in this case) for a bootstrap confidence interval of four mites (adults + nymphs) cm(-2) is sufficient to standardize the sampling-procedures for quantifying mites on soybean leaflets.

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).

ResumoA aplicação de inseticidas é a forma mais utilizada no controle de percevejos na cultura da soja, sendo a escolha da tecnologia de aplicação e do inseticida fundamental para obtenção de um controle eficiente. O experimento foi desenvolvido em lavoura comercial de soja, na safra agrícola 2008/09, em São Sepé, RS, com o objetivo de avaliar a eficiência de três métodos de aplicação e dois inseticidas no controle de percevejos na soja. O delineamento experimental utilizado foi inteiramente casualizado, em esquema fatorial 3x2+1 testemunha, com cinco repetições. As unidades experimentais tiveram dimensões de 40,0 x 40,0 m. O fator A foi representado pelos métodos de aplicação, sendo: A1-Terrestre com pontas hidráulicas, A2-Aérea, com atomizadores rotativos de discos e A3-Aérea, com pontas hidráulicas. O fator B foi representado pelos inseticidas sendo: B1-tiametoxam + lambda-cialotrina e B2-acefato. As aplicações terrestres e aéreas com baixo volume oleoso apresentam maior eficiência no controle de percevejos na cultura da soja, refletindo-se este controle em maior rendimento de grãos. Os inseticidas tiametoxam + lambda-cialotrina e acefato apresentam controle de percevejos e efeito residual semelhante. Palavras-chave: Controle químico, baixo volume oleoso, pentatomidae AbstractInsecticides application is the most widely used form to control stink bugs in soybean, being the application technology and the insecticide used the major factors for an efficient control. The experiment was conducted in a soybean field during the 2008/09 growing season, in São Sepé, RS, in order to evaluate efficiency of three methods of application and two insecticides for controlling stink bugs in soybeans. The experimental design used was completely randomized, in a factorial scheme 3x2 +1 control, with five replicates. The experimental units had dimensions of 40.0 x 40.0 m. The factor A was represented by the methods of application, as follows: A1-Tractorized spray with hydraulic nozzle; A2-Aerial, with rotary disc atomizers and A3-Aerial, with hydraulic nozzles. The factor B was represented by the insecticides, as follows: B1-thiamethoxam + lambda-cyhalothrin and B2-acephate. Ground and aerial applications with low volume oily had greater efficiency for controlling stink bugs in soybean, where led to an increase in soybean grain yield. Insecticides thiamethoxam + lambda-cyhalothrin and acephate were similar in controlling stink bugs and in residual effect.