The influence of the two-spotted spider mite (<i>Tetranychus urticae</i>) on yield of apple trees was investigated. The experiment was conducted on rrigated and non-irrigated 5-years-old apple trees of 'Close' and 'Jonagold' cultivars grafted on M.9. The population size of the pest exceeded four and two times the valid (in Poland) economic injury level on trees of 'Close' and 'Jonagold' cultivars respectively. No significant influence of mites on yield and its quality (mean fruit weight and fruit colour) was observed on both apple cultivars. Irrigation had positive effect on yield and quality of 'Jonagold'. On the contrary, trees of ' Close' cultivar were positively influenced by irrigation only regarding fruits colour. Results of the study support opinion that the economic injury level for apple orchards, with respect to two-spotted spider mite, should be higher than it is up to now.