Consecutive wet days may impede fruit quality of peach and nectarine and cause fruit drop

Extreme rainfall events pose a threating factor for the income of growers, processing industry and communities; however little is known on damages caused on peach trees. The pattern of historical trends in precipitation and the Standardized Precipitation Index (SPI) characteristics during the summer months were studied in Naoussa, Northern Greece. Damages from naturally occurring summer rainfalls were recorded in a peach and nectarine cultivar evaluation orchard and effects from a simulated rainfall experiment using prolonged (100 mm in 3 days) and intense (100 mm in 1 day) rainfall treatments were monitored on peach cv. 'Elegant Lady' trees. Results showed that during the summer months of 1967-2019, there was no significant effect in the precipitation totals and the Standardized Precipitation Index (SPI) characteristics, although an increase in the frequency of wet spells is noticeable in the last three years. Fruit drop and symptoms of skin streaking, bronzing, and collapse in skin tissue of peach and nectarine cultivars close to maturity initiated during and continued after the end of severe and extreme wet spells of three or more consecutive rainy days in a summer month in 2017, 2018 (total ca. 100 mm) and 2019 (total 54 mm) were recorded. The type of skin damages differed among peach and nectarine cultivars. Greater extent of damages was documented in the peach cvs 'Kevina (R)', 'Maura (R) ' and 'Royal Time (R) ' and fewer damages in 'Red Haven', and 'Sweet Scarlet'. The rainfall simulation experiment showed that only the prolonged, and not the intense treatment, caused fruit drop starting two days after the treatment initiation and lasted three days after the end, while streaking symptoms developed mostly in fruit from the prolonged rainfall treatment. In conclusion, the consecutive wet days rather than the total rainfall caused fruit drop and skin damages in peach and nectarine fruits close to harvest, while cultivars differed in the type of damage developing. Insurance programs need to be readdressed, incorporating rainfall frequency rather than total monthly rainfall as indicators of yield, as well as including the symptoms of fruit drop, skin streaking, bronzing and collapse as damages rather than cracking in peach and nectarine.