EXCESSIVE RAIN/SPLITTING

This pest affects:

Identification
Fruit

Minor breaks, which are only skin deep to ruptures extending the length of the fruit and deep into the flesh
Small star or crescent-shaped or concentric rings at the apical end
Circular or semi-circular cracks at the stem end
Long irregular cracks along the sides

Period of Activity
When rainfall occurs shortly before harvest.

Biology
When rainfall occurs shortly before harvest cherries will frequently split. This is a result of rapid uptake of water through the cuticle driven by the difference in the osmotic potentials of the rain water outside and the sugars and other chemicals inside the cherry flesh. Recent research has shown that some cracking may be caused, and all cracking made worse, by high water levels in the rest of the tree, and high humidity surrounding the tree.

Fruits sensitive to cracking often show many small imperfections on the skin surface (cuticle microcracks). These are usually invisible to the naked eye and are only observable through the microscope. Whether these microcracks have a part to play in facilitating water uptake or weakening cell bonding in the fruit epidermis, both of which would promote cracking, is not yet known. A discontinuous water supply, where trees become water-stressed between irrigations increased the amount of cuticular fractures.

The cuticle becomes thinner during the rapid period of growth between pit hardening and harvest.

The severity of cracking depends upon a number of factors, which include the variety, the stage of maturity, the length of the rainy period, and the air temperature.

Varieties with thick cuticles are able to absorb more water before splitting than those with thinner cuticle. Firm-fleshed cherry cultivars have greater tendency to fruit cracking than soft-fleshed ones. Bing is the variety most susceptible to cracking. Varieties considered of moderate susceptibility include Van, Stella, Sweetheart, Lapins and Vega. Low susceptibility varieties include Vista, Viva, Schmidt and Vic.

More water is taken up by the tree and fruit when temperatures are quite warm following rain. The driving force for this uptake is the osmotic concentration of the fruit juices, i.e., their soluble solids (sugars) concentration. The higher the concentration of soluble solids in the fruit juice (more mature fruit), the more water is expected to move into the fruit.

Management
Harvest fruit as soon as possible following a rain. Harvest lightly cropped trees or trees in weaker ground first. The longer the fruit remains on the tree and the higher the humidity the greater the cracking potential.

Some information included above excerpted from;

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Tender fruit

EXCESSIVE RAIN/SPLITTING