To develop methods of predicting the harvesting date for Japanese chestnut cv 'Tanzawa', 'Tsukuba' and 'Ishizuchi', full flowering and harvesting dates recorded for 44 years were analyzed. There were positive correlations between the harvesting dates and full female flowering dates. Predictive formulas to calculate harvesting dates were obtained from the regressions. The RMSEs (root mean square error) were 4.3-4.9 days. There were inverse correlations between the number of days to maturity and

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... he mean air temperatures for about 30 days from full female flowering dates. A second predictive formula of harvesting dates was obtained from the regressions. The RMSEs were 3.7-5.0 days. There were positive correlations between the number of days to maturity and the mean air temperature for a specific time in the late maturation period. A third predictive formula was obtained from the regressions. The RMSEs were 3.0-3.3 days. A practical technique consisting of three steps was developed as a method of predicting the harvesting date for Japanese chestnut.