Dry Matter Partitioning of Nonbearing Apple Trees Following Injury by European Red Mite (Acari: Tetranychidae)

Abstract

Apple trees ( Malus × domestica Borkhauser) of ‘Bisbee Delicious’ (a spur type), ‘Triple Red Delicious’ (a nonspur type), ‘Golden Delicious’, and ‘Red Stayman 201’ were subjected to various levels of European red mite, Panonychus ulmi (Koch), injury for 3 yr after planting. Mite injury (as measured by the mean seasonal cumulative mite days for the 3 seasons) ranged from 35 to 1,821 for the experimental trees. Dry matter accumulation in tree partitions was measured at the end of the 3rd growing season, and the effect of mite injury was analyzed. All 4 cultivars tested responded to mite injury in a similar manner, although tree size was influenced greatly by intrinsic differences among cultivars. Reductions in dry matter accumulation in the tree as a whole, the aerial portions, and the root systems occurred as a result of mite injury. The percentage of reduction per 1,000 mite days was greatest for the root system (7-12%), whereas reductions in other partitions averaged about 6%. The effect of mite injury during the non bearing phase, although statistically significant, is not a likely critical factor in the establishment and early production of an orchard. The importance of establishing biological mite control with Stethorus punctum (LeConte) early in the life of an orchard outweighs any negative effects on early growth.