Objective  Based on the inverse relation between the fruit cracking rate and fruit shape index (FSI), thresholds to achieve optimal pomelo thinning on Duweiwendan, Citrus grandis (L.) Osbeck. cv. Duweiwendan, was studied for orchard management.

  Method  From 2016 to 2018, 8 660 pomelos on Duweiwendan trees were collected from the major producing areas in Xianyou County, Fujian to determine the fruit crack width (FCW) and FSI at the orchards. Distribution of the data compiled was used to access the cost/benefit to arrive at a recommended threshold for the fruit thinning.

  Result  The upper limit of FSI at 0.90 was found to be the inflection point on the iterative regression simulation of logistic cumulative curve of the operation. According to the curve, at FSI≤0.83 a relatively high efficiency of cracked fruit elimination was obtained. At FSI≤0.80, 20% of the pomelos were discarded resulting in a definition greater than 2.0. At an FSI＞0.80, the amount of thinned fruits increased significantly, while the corresponding gain dropped to below 2.0. Conversely, if the FSI was reduced to less than 0.80, the operational efficiency declined. The peak of the logistic cumulative curve on the 3-year fruit crack rates, as well as the field statistics, indicated that a thinning threshold at FSI≤0.80 was appropriate with little concern of excessive loss on the fruit harvest.

  Conclusion  An optimal threshold of FSI≤0.80 to improve the financial gain with a minimized harvest reduction was recommended for the Duweiwendan pomelo orchards. An FSI up to 0.83 could be considered in years when a bumper pomelo harvest is expected.