Impact of European red mite on Golden Delicious and Oregon Spur apples in Israel

To develop a damage threshold for the European red mite (ERM), Panonychus ulmi (Koch), the effect of ERM injury on fruit weight and return crop in the apple cultivars (CVs) Golden Delicious and Oregon Spur were studied in the Upper Galilee of Israel for two consecutive seasons. The ERM significantly affected the leaf colour, chlorophyll content, fruit weight and return harvest in both CVs. High population levels of 450 adult female cumulative mite days (ACMDs) reduced the fruit weight on Golden Delicious but not on Oregon Spur. Population levels above approximately 600 and 900 ACMDs in Golden Delicious and Oregon Spur, respectively, caused a substantial reduction in the return harvest. Because no damage was observed at low population levels, an action threshold of 150 ACMDs is recommended.