Compatibility of Bifenazate and Phytoseiulus persimilis for Management of Twospotted Spider Mites in North Carolina Staked Tomatoes

The twospotted spider mite (TSSM, Tetranychus urticae Koch) is a key pest of tomatoes (Solanum lycopersicon L. [Solanales: Solanaceae]) in North Carolina, and its management has relied principally on synthetic acaricides. Augmentative biological control of TSSM is a commonplace and effective management strategy in greenhouses worldwide, but in field-grown vegetable crops biocontrol of TSSM is poorly developed. We conducted small-plot field experiments in 2016 and 2019 to test the ability of the predatory mite, Phytoseiulus persimilis Athias-Henriot, to establish, disperse, and reduce TSSM in staked tomatoes, as well as test their compatibility with a commonly used reduced-risk acaricide, bifenazate (Acramite). Across both years, the most effective treatment for reducing TSSM was the combination of P. persimilis + Acramite. Phytoseiulus persimilis successfully established both years, but its population growth and dispersal were greater in 2016 than 2019. Acramite alone significantly reduced TSSM pressure in 2019 and P. persimilis alone did not reduce TSSM pressure below the control in either year. However, results in 2016 were influenced by the eventual dispersal of P. persimilis into all experimental plots, despite efforts to hinder their movement with corn barriers. Results in 2019 were influenced by the late-season invasion of TSSM into the trial, which delayed P. persimilis releases and influenced their establishment and growth. This study is the first to demonstrate the utility and limitations of P. persimilis in staked field tomatoes, which is a promising option for growers to manage TSSM in tomatoes in the southeast United States.

IMPACT OF CUCUMBER GENOTYPE ON THE DAMAGES CAUSED BY TWOSPOTTED SPIDER MITE AND EFFICIENCY OF BIOLOGICAL SPECIMENS

Due to the growing variety of vegetables, the impact of genotypic parameters of plants on pest resistance and efficiency of biological specimens is of high importance when selecting and creating new varieties and hybrids. The researchers found out the significant differences in stability of parental forms, hybrids and cucumber varieties of the Siberian selection in relation to twospotted spider mite. The paper finds out relatively resistant parental forms - ZhL-4 and GP-61/b, and also samples of the paternal form - GF-7 and a maternal line - ZhL-9 damaged by a phytophage in a strong degree have been defined rather steady against a phytophage. High acaricidal effect of Phytoverm was found on all studied varietal samples, however the most effective biospecimen restrained development of the pest on plants of relatively resistant to phytophage of female line ZL-4. Reproduction of the twospotted spider phytoseiulus did not depend on genotypic features of parental forms, varieties and hybrids of cucumbers. The number of acarifages increased by 7.8-8.2 times in two weeks after appearance on the plants inhabited by spider mite in comparison with the initial number, as a result of which the damage rate of plants by the pest of most cultivars decreased, and in male forms practically did not change (GF-19) or slightly increased (GF-7). According to biochemical parameters, cucumber varieties with different degree of resistance to phytophage differed in dry matter content. Non-resistant to twospotted spider mite female forms LL-9, LL-12/1 and Nadezhda variety contained the lowest concentration of dry matter (5.4%), the highest amount of dry matter was observed in female line LL-4, which has the highest pest resistance (6.0%). Since the inherited traits are predominantly transmitted by the maternal component and the paternal form enhances these properties, it is important to assess not only the yield and flavour qualities but also the degree of resistance of parental forms to pests when selecting cucumber varieties and hybrids.