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Validation of Injury Thresholds for European Red Mite (Acari: Tetranychidae) on 'Yorking' and 'Delicious' Apple

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Injury thresholds for the European red mite, Panonychus ulmi (Koch), were validated for two major apple (Malus x domestica Borkhauser) cultivars, 'Yorking' and 'Delicious,' in Pennsylvania. Four tarl!;etinjury thresholds (0, 250, 750, and 1,250 cumulative mite days [CMDl per leaf) were established on trees for 1 or 2 yr. Most of mite injury occurred during July and August. Effects of injury were determined on mean fruit weight, soluble solids, fruit firmness, fruit color, as well as return bloom, percentage of fruit set, and fruit load the year following injury. Only the target injury threshold level of 1,250 CMDs caused any reduction in yield variables, and this occurred only during the year after mite injury. These reductions occurred for return bloom, percentage of fruit set, and return fruit load and only for the cultivar Yorking.' Mite injury had no effect during current season. Adoption of an injury threshold of 750 CMDs is proposed for apples in Pennsylvania. Hypotheses are presented to help explain differences in results of our study compared with those of previous studies.

Document Type: Research Article

Publication date: October 1, 1990

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  • Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.
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