Damage assessment and economic injury level of the two-spotted spider mite Tetranychus urticae in soybean

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).

Cover crops affect soybean yield components, but not grain quality

“…The leaf S2. Values are mean ± SD (n = 3) (grey shaded area) area damage and the abundance of two-spotted spider mites were not evaluated in 2017, but Padilha et al (2020) calculated a decrease in soybean yield of one pod plant −1 , 0.7 g TKM, and 0.42 g m −2 by an infestation rate of one spi-der mite leaf area cm −2 . However, the observed grain yield components in the current study showed that soybean had a high potential of adaptation and indicates grain density as a robust parameter over both years.…”

Population fluctuations of Tetranychus urticae Koch and the associated predatory mite, Euseius scutalis (A.-H.) on three soybean cultivars at Gharbia governorate

“…The population dynamics of T. urticae showed that infestation increased gradually from mid-June day reached its maximum at the end of July, and then decreased gradually at the beginning of Aug., reached its minimum number at the beginning of Sept. before the harvest time. Padilha et al (2020) reported the reduction of soybean grain yield caused by T. urticae damage. The population density of one T. urticae per cm 2 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 .…”

Small‐scale dispersal and gene flow of the agricultural pest two‐spotted spider mite in apple orchards: Implication from landscape ecological and population genetic analyses

“…The two‐spotted spider mite, Tetranychus urticae Koch (Acarina, Tetranychidae), is a highly damaging agricultural pest around the world (Bamel & Gulati, 2021; Padilha et al, 2020; Sun et al, 2012; Tehri, 2014) with remarkable dispersal abilities (Smitley & Kennedy, 1985). It has become a global concern due to its rapid development, high fecundity, ability to feed on over 1100 plant species, and rapid evolution of pesticide resistance (Grbić et al, 2011).…”