Flower thinning effect of synthetic auxins on `Fuji' apple

摘要

Apple cv. Fuji now accounts for >50% of the total apple production in Japan. Fuji tends to over-set but carbaryl has little effect as a fruit thinner. In this study, conducted from 1991 to 1993, the effects of 6 synthetic auxins on flower thinning were examined. NAA, dichlorprop, MCPB ethyl and N-(1,3-dimethyl-1H-pyrazol-5-yl)-2- [(3,5,6-trichloro-2-pyridinyl)oxy]acetamide (experimental code name: NSK-905) caused thinning when applied just after full bloom. Ethychlozate and 4-CPA had no effect. Adequate thinning was achieved by spraying NAA at 20 p.p.m., dichlorprop at 45 p.p.m., MCPB ethyl at 30 p.p.m. or NSK-905 at 100-200 p.p.m. 1 day after full bloom. In addition to leaf abnormality, severe epinasty was observed with NAA and dichlorprop. Epinasty was also observed with MCPB ethyl but it was slight and did not influence the growth of shoots and fruits. These results indicate that treatment with MCPB ethyl or NSK-905 immediately after full bloom has potential for thinning of Fuji flowers.