Estimation of economic injury levels and action thresholds for the two-spotted spider mite, Tetranychus urticae Koch, on strawberry plants

Abstract

Strawberry ( Fragaria × ananassa Duch.) is a high-value global crop, yet its productivity is severely constrained by the two-spotted spider mite, Tetranychus urticae Koch. Developing localized economic thresholds is a cornerstone of sustainable Integrated Pest Management (IPM) to mitigate yield losses and reduce acaricide reliance. This two-season field study (2019–2020) investigated the quantitative relationship between T. urticae population density and strawberry yield in Egypt. Using varying infestation levels established via Chitosan (Top9 0.1%) treatments, linear regression and Chi-square (χ 2 ) analyses were employed to determine four critical economic levels: General Equilibrium Position (GEP), Economic Threshold Level (ETL), Economic Injury Level (EIL), and Economic Damage Level (EDL). Results revealed a highly significant negative correlation between mite density and yield ( r = -0.96*** in 2019; r = -0.97*** in 2020), with an average yield reduction of 1.25% per mite. The estimated EIL and ETL were 4.0 mites/leaf in 2019 and 3.4 mites/leaf in 2020. These findings provide a precise decision-making framework for mite management in Mediterranean strawberry production. The low estimated thresholds suggest that proactive, preventive management strategies are more effective than reactive control to maintain strawberry yield.

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