Abstract
Warabieda W. (2015): Effect of two-spotted spider mite population (Tetranychus urticae Koch) on growth parameters and yield of the summer apple cv. Katja. Hort. Sci. (Prague), 42: 167–175. The effect of two-spotted spider mite populations (Tetranychus urticae Koch) on the yield and growth parameters of the early-season apple cv. Katja was evaluated during a 3-year study. In the case of the colonisation of apple trees exceeding 1,462, 2,760 and 1,548 cumulative mite days (CMDs) in the subsequent years of research, a significant reduction of the cumulative yield (14 kg/tree) and of the cumulative trunk cross sectional area increase (5.7 cm2) was observed. No significant effect of spider mites on the average weight of the fruit was observed, while the pest affected fruit colouration. The calculated values of economic injury level were 60.5, 155.5 and 51.8 CMDs in subsequent years of the study, respectively. These values are much lower than the action threshold recommended in Poland and elaborated for the European red mite – Panonychus ulmi (Koch) on apple trees. The results suggest that the tolerance of early-season apple cultivars to T. urticae may be lower when compared to late-season varieties infested with P. ulmi; therefore, the decision to implement pest management for two-spotted spider mite should be taken at a lower infestation threshold than previously thought.
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