Testing the contact and residual toxicity of selected low-risk pesticides to Tetranychus Urticae Koch and its Predators

Abstract

Occasionally Tetranychus urticae, two-spotted spider mite (TSSM), become a major problem in crops. TSSM is mainly controlled with synthetic acaricides. Some low-risk pesticide options are available and included in IPM. In this study, contact and residual toxicity of selected low-risk pesticides were tested against TSSM adult females and three commonly available predators (Phytoseiulus persimilis Athias-Henriot, Neoseiulus fallacis McGregor and Stethorus punctillum Weise). TSSM adult females and adults of TSSM predators were released on the leaf discs either before spray (contact bioassay) or after the spray (residual bioassay). In contact bioassay, all of the tested pesticides killed more than 95% of the TSSM after 72 hours except diatomaceous earth (DE). Diatomaceous earth killed only 24.6+3.2% TSSM that was significantly lower than all the other pesticides used. When mites were released onto treated leaf discs (spray residues), only garlic/chilli extract gave relatively acceptable levels of mortality 72.0+5.8% while bifenazate caused 95.2+3.7% mortality. TSSM females laid significantly more eggs on the garlic/chilli treated leaf discs in both contact and residual bioassays. When sprayed directly (contact bioassay), all of tested low-risk pesticides mortality of 85.2-100% to P. persimilis except DE. All of tested low-risk pesticides were moderately harmful to N. fallacis and S. punctillum causing 30.5-83.6% and 34.6-78.6% mortality, respectively. All of the tested low-risk pesticides were harmless to slightly harmful in the residual toxicity bioassay causing 6.8% - 39.4% mortality in all predators tested. In conclusion, predators could possibly be released 2-3 days after application of any of the tested low-risk pesticide.