Effect of European red mite (Acari: Tetranychidae) injury on vegetative growth and flowering of four cultivars of apples

Effect of European red mites (ERM), Panonychus ulmi (Koch), on nonbearing spur-type and standard 'Delicious', 'Golden Delicious', and 'Stayman' apple trees was compared over a 3-yr period. Mite population levels ranged from ca. 0-2,000 mite-d, with each tree receiving about the same amount of mite-days each year. Shoot length, leaf numbers, and trunk girth were little affected by mite damage, but early defoliation occurred on 'Golden Delicious' and standard 'Delicious'. Flowering was reduced on 'Golden Delicious' and 'Stayman', but not on either of the 'Delicious' types. In general, 'Delicious' appeared to be more tolerant of ERM damage.