INFLUENCE OF EUROPEAN RED-MITE ON LEAF AND WHOLE-CANOPY CARBON-DIOXIDE EXCHANGE, YIELD, FRUIT SIZE, QUALITY, AND RETURN CROPPING IN STARKRIMSON-DELICIOUS APPLE-TREES

The hypothesis was tested that effects of late-season European Red Mit e (ERM) [Panonychus ulmi (Koch)] injury on apple (Malus domestica Bork h.) fruit development are better explained by carbon physiology than b y pest densities, Midseason ERM populations were allowed to develop in mature semi-dwarf 'Starkrimson Delicious'/M26 trees with moderately h eavy crops, then were controlled with miticides at different mite-day (activity of one mite per leaf for 1 day) levels as estimated by weekl y leaf sampling. The range of final mite-days was from 250 to 2100 on individual trees. Seasonal fruit growth patterns were monitored. Diurn al whole-canopy net CO2 exchange rate (NCER) was measured in eight cle ar flexible balloon whole-canopy chambers on several dates before and after mite infestations, Mite injury reduced fruit growth rates, Leaf and whole-canopy NCER were reduced similarly, Late season fruit growth . and final fruit size were correlated with accumulated mite-days, but were better correlated to whole-canopy NCER per fruit, Fruit firmness , color, soluble solids and starch ratings showed no correlation to mi te-days. Number of flower clusters per tree and final fruit per tree t he following year were not related to accumulated mite-days, but final fruit per tree the following year were better correlated to whole-can opy NCER per fruit. These results generally supported the hypothesis.