Relationships Between Leaf : Fruit Ratio and Varying Levels of European Red Mite Stress on Fruit Size and Return Bloom of Apple

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.

Management of Panonychus ulmi with Various Miticides and Insecticides and Their Toxicity to Predatory Mites Conserved for Biological Mite Control in Eastern U.S. Apple Orchards

“…All treatments exceeded the 1 predator/10 P. ulmi (0.1) needed for biological control within 2 weeks of the 11 July application which resulted in a crash in both P. ulmi motile and egg populations after this time. Simplistic efficacy spray thresholds by manufacturers on their product labels also do not take into account the variable economic injury thresholds for P. ulmi in eastern apple orchards that change during the season due to many factors such as crop load, water stress, and age and size of the trees [ 13 , 16 , 49 ]. These have resulted in current action thresholds for Pennsylvania apple orchards of 3–5 mpl for P. ulmi populations before early to mid-June, 5–12 mpl for late June to early July and 8–25 mpl for mite populations after mid-July depending on the general stress trees are under due to crop load and water stress [ 12 ].…”