Influence of European Red Mite (Acari: Tetranychidae) and Crop Density on Fruit Size and Quality and on Crop Value of ‘Delicious’ Apples

Abstract

Yields of ‘Campbell Redchief Delicious’ ( Malus × domestica Borkhauser ) trees treated with factorial combinations of European red mite, Panonychus ulmi (Koch) populations (range, 0-3,000 cumulative mite days per leaf), and crop densities (range, 2 to 12 fruit’ cm-2 trunk cross sectional-area) were correlated positively to crop densities and negatively to cumulative mite days. Fruit weight, fruit surface red color, and fruit soluble solids concentration generally declined with increasing levels of cumulative mite days and crop densities. For most response variables, a significant cumulative mite days by crop densities interaction was observed. Crop value generally increased with increasing crop densities and declined with increasing cumulative mite days, and mite feeding reduced crop value greater at high crop densities. Crop value estimates were used to calculate economic injury levels. Adoption of economic injury levels of 1,000, 500, and 300 cumulative mite days is proposed for spur ‘Delicious’ trees in Virginia with light, moderate, and heavy crop loads, respectively.