The influence of the two-spotted spider mite (Tetranychus urticae) on yield of apple trees was investigated. The experiment was conducted on irrigated and non-irrigatted 5-years-old apple trees of' Close' and 'Jonagold' cultivars grafted on M. 9. The popula, size of the pest exceeded four and two times the valid (in Poland) economic injury on trees of' Close' and 'Jonagold' cultivars respectively. No significant influence of on yield and its quality (mean fruit weight and fruit colour) was observed on both cultivars. Irrigation had positive effect on yield and quality of 'Jonagoid'. On the 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, with respect to two-spotted spider mite, should be higher than it is up to now.