Assessment of damage caused by the spider mite Mononychellus planki (McGregor) on soybean cultivars in South America

Abstract

The aim of this study was to quantify the reduction in grain productivity caused by tetranychid mites in different soybean genotypes. For this purpose, two experiments were carried out in two different experimental sites, one with 20 and another with 25 soybean cultivars. The sites had distinct soil features and were chosen to verify the influence of local conditions in the manifestation of intrinsic soybean plant resistance to spider mites. The experimental design was of randomized blocks with subdivided plots and four replications. The effects of cultivars were assessed in plots 5 x 25 m and yield reduction was investigated in subplots regarding presence and absence of tetranychid mites. The presence of mites on each cultivar was checked weekly after the emergence of soybean plants, until the detection of its occurrence. To evaluate the mite population, 25 leaflets of the upper stratum and 25 of the lower stratum of plants were randomly collected from a 20 cm2 area to quantify the density of mites. The results showed that predominant species was Mononychellus planki (McGregor) (>90%). The other species such as Tetranychus urticae (Koch), Tetranychus ludeni (Zacher), Tetranychus gigas (Pritchard) and Tetranychus desertorum (Banks) were also observed. The population of mites and grain yield loss differed significantly depending on the soybean cultivar. The average reduction in soybean productivity in both experiments was 483 kg of soybean/hectare, corresponding to an average reduction of 20% of the productive potential of the cultivars evaluated. The spider mites can cause a great damage to soybean cultivar. Therefore, growers must regularly scout for its presence in the field, applying control measures as soon as the level of spider mites significantly increases.