Difference in the efficacy of NAC as thinning agent of apple [Malus pumila] fruit among several cultivars
1991
Fukuda, H. (Fruit Tree Research Station, Morioka (Japan). Morioka Branch)
The mode of action of NAC (carbaryl) used for the thinning of terminal and lateral fruits on a cluster was compared in 11 apple cultivars during 5 growing seasons. The average increase in the terminal fruit drop rate of the trees sprayed with the thinning agent over non-sprayed trees ranged from 10% to 20% for 9 out of 11 cultivars, indicating that there was no practical difference in the efficacy in the thinning of terminal fruits among the 9 cultivars; "American Summer Pearmain", "McIntosh", "Jonathan", "Golden Delicious", "Mutsu", "Fuji", "Ourei", "Indo" and "Ralls Janet". In these cultivars, over-thinning may occur when the natural (unsprayed) physiological fruit drop is high. In two cultivars; "Starking Delicious" and "Akane", the increase in the terminal fruit drop rate was about 30% in the former and almost 0% in the latter. The former cultivar may be prone to over-thinning, due to the higher efficacy of the thinning agent. The thinning efficacy for the lateral fruits did not differ from that of the terminal fruit
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