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Abstract
‘Delicious’, ‘Golden Delicious’, and ‘Yorking’ apple trees (Malus domestica Borkh.) were assessed in 1979-80 for the influence of foliar damage by the European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae) on preharvest drop with and without a stopdrop chemical 2-(2,4,5-trichlorophenoxy) propionic acid (2,4,5-TP). The cumulative percentage of fruit drop did not differ between uninjured and mite-injured trees at mite damage levels that included severe bronzing, nor was there any apparent reduction in the efficacy of the stopdrop spray due to mite damage. Commercially acceptable drop control was obtained with 2,4,5-TP regardless of mite damage. These data do not support the widely accepted view that the uptake and/or performance of stopdrop sprays is impaired on mite-injured apple trees.
Abstract
Fruit size and return bloom of apple (Malus domestica Brokh.) were examined in 1982-84 under varying levels of crop load and stress caused by the European red mite [Panonychus ulmi (Koch)]. Trees of ‘Rome Beauty’/MM.111 and ‘Yorking’ M.26 were subjected to two and three levels of mite stress, respectively, over a range of leaf : fruit ratios (LFRs). Regression models were used to explore the effect of LFR on fruit size and return bloom at the various mite injury levels. There was a curvilinear relationship between mean fruit weight and LFR for most of the check and mite-injured groups. The relationship between bloom density and LFR was linear over the range studied. Both experiments indicated reduced fruit size and return bloom with moderate to high mite damage, regardless of LFR.