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To control whiteflies on soybean crops in an effective and economically viable way, it is necessary to quantify the occurrence and density of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) on the leaflets. Estimating the number of B. tabaci cm‐2 on leaflets is difficult, because its distribution pattern on the various parts of the plant canopy and on the leaflet surface is unknown. The aim of this study was to evaluate the distribution of B. tabaci nymphs on soybean plants and leaflets, under greenhouse and field conditions. One hundred soybean plants infested with all nymph stages were randomly selected in a greenhouse, and 25 in a field. Of each plant, a trifoliate leaf of the middle third of the plant's height was selected and its central leaflet was collected (greenhouse experiment), or a trifoliate leaf of each third layer (upper, middle, and lower), of which the left, central, and right leaflets were collected (field experiment). The collected leaflets were divided into 32 sections (1 cm2 per section), arranged in an array of eight rows and four columns to count whitefly nymphs. The Morisita index (Iδ), the negative binomial parameter k, and the dispersion index (I) were calculated for each leaflet, using the number of nymphs as variable. The highest population densities of whitefly nymphs were found in the middle third of the soybean plants. In leaflets from the middle third, the nymphs concentrated in the middle and bottom parts of the leaflets, whereas in the upper and lower thirds of the plant, they were randomly distributed on the leaflets. [ABSTRACT FROM AUTHOR]

Biometric techniques, including the principal component analysis, are commonly applied in soybean genetic divergence studies. However, the sample size used in such studies is often determined empirically, neglecting its potential impact on inference interpretation. Therefore, this study aimed (i) to analyze the response of principal components to the number of plants sampled per experimental unit (plot); (ii) to determine the multivariate representative sample size, and (iii) to construct a methodology to predict sample size for principal components as a function of the precision level defined a priori. Six experiments were performed in two locations in Rio Grande do Sul, Brazil, with three experiments being carried out in each location. All experiments were conducted using a complete randomized block design with three repetitions, and 20 soybean genotypes were utilized, resulting in 360 plots (60 plots per experiment). From each plot, twenty plants were sampled, totaling 7200 plants. A resampling bootstrap procedure was applied to the principal component technique for 10 biometric traits. Posteriorly, the sample size was defined based on predefined precision levels, and power logistic models were parametrized to predict the sample size per experimental unit. The precision of the eigenvalues obtained from the principal component analysis gradually improves with larger sample sizes. Eigenvalues that capture a higher variance tend to require smaller sample sizes for accurate estimation. The fitted models demonstrated satisfactory predictive ability in determining the optimal number of plants per experimental unit, serving as a complementary tool for defining sample size at the desired precision level. Eighteen plants per experimental unit are enough to estimate the eigenvalues of the first two soybean principal components reliably. The developed predictive methodology and sample dimensioning per experimental unit can support future research aimed at identifying divergent genotypes, making them useful tools for soybean plant breeding programs. [Display omitted] • Principal component estimates are improved as sample sizes increases. • Eighteen plants per experimental unit were enough to analyze genetic divergence. • An accurate methodology to predict sample size per experimental unit was developed. [ABSTRACT FROM AUTHOR]

Soybean is the main agricultural crop produced and exported by Brazil, and the whitefly, Bemisia tabaci (Gennadius, 1889) (Hemiptera: Aleyrodidae), is one of the main pests of this crop. Whitefly control is carried out mainly with chemical insecticides, which has led to an increase in number of applications and evolution towards resistant populations. There is a need to study alternatives for the control of this insect pest, and biological control using entomopathogenic fungi can be an effective tool, offering less risk to the environment. This study aimed to design and evaluate four management programs in two soybean cropping seasons, including two integrated management alternatives, a conventional chemical management alternative and a biological (fungal) control alternative. Two sequential sprays set 10 days apart were performed for each program, and the results of ANOVA and Scott-Knott test (P ≤ 0.05) revealed differences among treatments. The integrated management consisting of a sequential spray of chemical insecticide followed by a fungal one stood out as the best control option, presenting 60% of control efficacy for whitefly adults and 34% for whitefly nymphs in the first cropping season; 83% of control efficacy for whitefly adults and 53% for whitefly nymphs in the second cropping season. Therefore, integrating fungi-based products with chemical insecticides may provide an efficient alternative for controlling B. tabaci in soybean. • Integrating entomopathogenic fungi-based products with chemical insecticides enhances B. tabaci control in soybean. • Applying fungi-based products after two sprays of chemical insecticides provides 60–83% of control for whitefly adults. • This strategy is more effective for B. tabaci control than applying fungal products in the first spray or alone. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the herbicidal activity of picloram on the biomass of the remediation plantsEleusine coracanaandPanicum maximumafter cultivation in a soil contaminated with this herbicide. These species were grown in three soils, differentiated based on texture (clayish, middle, and sandy, with 460, 250, and 40 g kg–1of the clay, respectively), previously contaminated with picloram (0, 80, and 160 g ha–1). After 90 days, the plants were harvested and an extract was produced by maceration of leaves and stems of these plants. It was applied to pots containing washed sand, comprising a bioassay in a growth chamber using soybean as a bioindicator for picloram. Soil and plant samples were analyzed by HPLC. The results showed the presence of picloram or metabolites with herbicidal activity in the shoots ofE. coracanaandP. maximumat phytotoxic levels with regard to soybean plants, indicating that they work only as phytoextractors and that the presence of straw on the soil surface can promote recontamination within the area. It is not recommended to cultivate species susceptible to picloram in areas where it was reported remediation byE. indicaandP. maximumand still present residues of these species. [ABSTRACT FROM PUBLISHER]

The whitefly Bemisia tabaci is the second most widespread and economically important arthropod pest in the world, with frequent population outbreaks occurring in Brazil and increasing economic damage on soybean crops. High oviposition rate, short life cycle and uneven distribution along the plants' canopy favour the dissemination of B. tabaci within soybean crops and compromise the efficacy of control measures. The objective of this work was to quantify soybean yield reduction caused by B. tabaci damage and propose an economic injury level (EIL) for this pest in soybean crops. Experimental design was randomized blocks with four replicates. Soybean grain yield and its components (number of pods, number of grains and 1000-grain weight) were quantified in relation to different levels of B. tabaci infestation in two cropping seasons, obtained through insecticide sprays carried out at different growth stages of the soybean plants. The resulting data were submitted to variance analysis, mean separation test and regression analysis. We found that a population density of one whitefly trifoliate−1 reduces from 0.88 to 1.79 grains plant−1, 0.16 ± 0.01 g plant−1 or 31.24 ± 4.21 kg ha−1of grain yield, and varies in response for pods plant−1 and 1000-grains weight. Based on this information, we suggest an economic injury level of 1.465 ± 0.195 B. tabaci trifoliate−1, considering a control cost of US$ 20.00 ha-1 and soybean crop value of US$ 400.00 tonne−1. • The number of B. tabaci soybean trifoliate−1 is decisive for the level of control. • The population peak was reached during soybean reproductive phases. • The economic injury level of B. tabaci in soybean is 1.465 ± 0.195 trifoliate−1. • One B. tabaci trifoliate−1 reduced 0.16 ± 0.01 g plant−1 or 31.24 ± 4.21 kg ha−1. • One B. tabaci trifoliate−1 reduced 0.88 to 1.79 grains plant−1. [ABSTRACT FROM AUTHOR]