The prodigious and regular rainfall we have experienced this Spring may be good for some things, but it is not good for ripening blueberries. As you can see in the photo below, excess rainfall can cause blueberry fruit to split rendering it unsaleable and inedible.
So, how does this happen? First off, water splitting happens in other fruits too. More study has been done on cherries than most other fruits. Reasons that cherries split are related to cultivar, fruit maturity, temperature of the water that hits the fruit, temperature of the fruit itself, duration of wetness, sugar content, fruit firmness, turgor pressure within the fruit, relative humidity, soil moisture, permeability of the skin and elasticity of the skin. In blueberries, studies have shown that absorbed water through the skin is one reason, but also via root system uptake (although less so than direct contact). The incidence of rain-caused splitting is very cultivar dependent and that cultivars with firmer fruit may be more susceptible to splitting. What, within the fruit itself, could lead to this? Some studies have suggested that in some cultivars the amount of air-filled spaces between cells could allow more water to enter but not split. Another stated that cells that weakly adhere to each other may split more readily. A recent study showed that there is a moderately high heritability for fruit splitting, suggesting that this trait can be improved to some degree through plant breeding.
A past survey of MS and LA growers found that fruit splitting could reduce marketable yield by as much as 20% in some cultivars. This means that cultivar choice is very important to avoid this type of damage. Results from different studies mostly agree on results of what cultivars split more than others. Below I have put them into three different categories: ~10% split or less (Low); ~10-19% (Moderate); ~20+% (High).
Low: Alapaha, Austin, Premier, Magnolia, Jubilee
Moderate: Gulf Coast, Chaucer, Columbus, Powderblue, Ochlockonee, Vernon
High: Brightwell (there was discrepancy on this cultivar, but 2 of 3 studies showed it to be high), Climax, Tifblue, Pearl River
One study found that excluding rainfall from the plants (covering them) was not a sure way of eliminating split, although it did reduce it. Also, fruit on plants that are overhead irrigated appear less likely to split than those on drip irrigation. New products are now on the market that may help reduce fruit split damage. They have not been tested in Mississippi, but have been tested in Florida and Georgia with encouraging results.
For further information you may refer to the papers below:
D. Marshall et al. 2008. Blueberry splitting tendencies as predicted by fruit firmness. HortScience 43:567-570.
D. Marshall et al. 2007. Laboratory method to estimate rain-induced splitting in cultivated blueberries. HortScience 42:1551-1553.
D. Marshall et al. 2009. Water uptake threshold of rabbiteye blueberries and its influence on fruit splitting. HortScience 44:2035-2037.
D. Marshall et al. 2006. Splitting severity among rabbiteye blueberry cultivars in Mississippi and Louisiana. Intl. J. Fruit Science 6:77-81.
D.S. NeSmith. 2005. Evaluation of fruit cracking in rabbiteye blueberry germplasm. Southern Region Small Fruit Consortium Research Project Progress Report.
M. Dossett and C. Kempler. 2015. Heritability of fruit splitting tendency in blueberry. HortScience (in press) abstract.