Answer: Generally speaking, high light and high temperature conditions in the summer can cause varying degrees of stress that are manifested in different ways. First, if there is inadequate rainfall or an inability to irrigate, such conditions can cause drought stress. Foliage may wilt, especially in the afternoons, and, under very severe conditions, some premature defoliation can result. Second, ripening fruit may actually drop off the tree prematurely. Third, fruit that are well exposed to the sun can also experience sunburn causing them to be unmarketable. Fourth, larger branches or scaffold limbs that are not shaded by in-canopy foliage and that are directly exposed to the sun may be sunburned. This is evidenced by bark cracking, peeling and even exposure of underlying wood. Finally, flower buds for next year’s crop are initiated this summer. Sustained periods of high temperature during the flower initiation phase can cause the production of 1, 2, or 3 pistils. If pollinated, this may cause single, double, or triple fruit. These double and triples (twins or triplets) are fused together and need to be thinned off because the resultant fruit are unmarketable. Sometimes with doubles (twins), one fruit may abort and the resultant peach will have a malformed suture at harvest also making it unmarketable.
|Hot, sunny, dry conditions may cause leaves to wilt in the afternoon sun. Several days of these conditions may cause some foliage to drop off the tree (seen as brown leaves on the orchard floor below).
||If severely stressed because of high temperature and insufficient rainfall, premature fruit drop may occur (note fruit on orchard floor below).
|Fruit that are exposed to high sunlight and high temperature conditions near harvest may experience sunburn to the skin that can cause cracking and fruit are no longer marketable.
||This is a scaffold limb that suffered severe sunburn damage in prior years. Note how the outer bark has split and is peeling back while the underlying wood is also split and dead.
|High temperatures during floral initiation can cause the production of double or triple (twin or triplet) fruits. The single fruit is normal.