Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
We recently have had wet weather in many parts of Delmarva. Excess moisture can cause problems in fruit crops due to fruit cracking.
Of the fruit crops, sweet cherries and certain plums are the most sensitive to excess moisture. Cracking due to excess moisture is a major reason that we have problems growing sweet cherries on Delmarva. It is not the uptake of water through the plant root system that causes the cracking; it is the absorption of water through the fruit cuticle that causes the fruit splitting. The theory is that as a cherry or plum ripens and accumulates sugars fruit exposed to extended periods of wetness from rain, dew, or high humidity conditions will absorb water through the fruit skin and swell until the fruit cracks. Some cherry and plum varieties are more susceptible to cracking than others.
Growers of sweet cherries in the east often lose large portions of their crop due to fruit cracking. In the past, the tools that growers have used are to physically remove water from cherry fruit surfaces using helicopters or blower sprayers. Use of calcium chloride sprays prior to rain events act to reduce the osmotic potential of rainwater. Chemical barriers have also been tried to prevent water movement into the fruit with varying success. There has been great interest in the use of high tunnels with dwarf sweet cherries to control cracking by eliminating wetness on fruit surfaces with these plastic covers.
Similar skin cracking can occur in nectarines and peaches. When the skin of these fruits stays wet for an extended period near ripening, the fruit can absorb so much moisture that it cracks. This is a problem for growers that do “tree ripe” fruit. Earlier harvest and ripening off the tree can help control this problem.
Some blueberry varieties are also susceptible to fruit cracking at ripening. Research has shown that both fruit absorption of water and internal water accumulation from root uptake cause this cracking.
Japanese plum variety highly susceptible to fruit cracking in wet weather.