072 MITES AND CROP DENSITY INFLUENCE `DELICIOUS' APPLES

Abstract

`Campbell Redchief Delicious' trees were treated with a factorial combination of five European red mite (ERM) populations (range = 0 to 3000 cumulative mite-days per leaf (CMD)), and four crop densities (CD) (range = 2 to 12 fruit · cm-2 trunk cross sectional-area) during two growing seasons. Yield was related positively to CD and negatively to CMD. In general, fruit weight, fruit surface red color, and fruit soluble solids concentration declined with increasing levels of CMD and CD. For most response variables, there was a significant CMD by CD interaction. Fruit were graded into six size categories and crop value was calculated. Crop value generally increased with increasing CD and declined with increasing CMD, mite feeding reduced crop value most at high CD. Crop value estimates were used to calculate economic injury levels. We propose economic injury levels of 1000, 500, and 300 CMD, respectively for spur `Delicious' trees with light, moderate, and heavy crop loads.