The mechanism of yield suppression by a triadimefon fungicide programme on the apple cv Cox’s Orange Pippin

Abstract

SummaryBlossom characteristics and fruit-set of the apple cv Cox’s Orange Pippin have been examined following spraying for four years with the fungicide triadimefon/bitertanol an ergosterol biosynthesis inhibitor (EBI). The EBI-treated trees did not give the usual mature tree response of increased flower production to a light crop in the previous season. Relative to a standard binapacryl spray flower bud development was delayed and both initial and final fruit-set were reduced by the EBI treatment. The flowers showed no differences in pollen tube growth but ovule longevity was reduced in the EBI flowers. The latter also tended to have smaller ovaries, indicating a possible limitation to fruit size.