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Abstract
Population levels of spider mites, principally European red mite, Panonychus ulmi (Koch), were regulated on ‘Newtown’ and ‘Golden Delicious’ apple trees for 4 years. Seasonal fruit sizing and firmness, terminal shoot growth, leaf chlorophyll content, and folio wing-year fruit set were evaluated against mite feeding intensity. Only leaf chlorophyll content of both cultivars and fruit firmness of ‘Golden Delicious’ were unfavorably influenced by mite feeding. Vigorous-growing, nonstressed apple trees possess a relatively high tolerance to seasonal average mite densities of ca. 30 mites/leaf without adverse effects.
Abstract
Dilute sprays of 4, 8 and 16% Volck Supreme oil at dormant and repeated at delayed dormant to mask pear trees against psylla, Psylla pyricola (Foerster), oviposition delayed bloom slightly, while 2% applications in the Meld advanced bloom less than 1 day. Dormant pear branches dipped under laboratory conditions in oil at concentrations of 8% and higher caused injury to vegetative buds and slight injury to flowering buds. Single and repeat field applications of oil at 2, 4 and 8% caused no reduction of fruit set or cropping of ‘Anjou’, ‘Bartlett’, ‘Cornice’, ‘Bose’, and ‘Seckel’ pear trees, and in some cases increased fruit set on ‘Anjou’ trees. Hormonal analysis of oil-treated buds indicated a slight increase of gibberellin (GA) and a reduction of abscisic acid (ABA) levels.