If you have fruit trees you are probably now getting a little tired of raking up fallen fruits which are the result of a natural occurrence known as the “June Drop”. This year the phenomenon is extending well into July, to the point that one wonders if there will be a crop left to harvest. So what is normal, and when do our trees need help?
Apples and pears produce several flowers on each cluster in spring, and depending on pollinator activity, and the local availability of another apple to cross pollinate, many, many flowers may set fruit. However, there will also be numerous little fruitlets that did not get pollinated properly, are damaged by insects, or require more carbohydrates than the tree can produce, and these fruits wither and fall off, frequently in large numbers.
As the remaining fruits begin to swell many more get attacked by codling moth, are affected by lack of sufficient water, or otherwise get damaged, and since the tree can only support a certain sized crop it goes through another round of shedding, usually beginning in June and continuing until early July, often resulting in carpets of larger fruit on the ground - frustratingly too immature to use for any practical purpose.
It is thought that warm nights may cause the fruit drop to be excessive since the respiration rate of the tree causes more carbohydrates to be consumed during the hours of darkness, leaving less available for fruit production.
Another factor could be lack of nitrogen, so a careful fertilization regime should be followed, being aware that too much nitrogen can also cause fruit drop and excessive growth. For information on fertilization see: http://homeorchard.ucanr.edu/The_Big_Picture/Fertilization/
In areas such as ours lack of water will also be a factor, so make sure that you check your irrigation system and remember to seasonally adjust the amount. A mature semi-dwarf tree can produce over 400 pounds of apples which, after all, are made up mainly of water!
On a large, heavy cropping tree, thinning young fruits early in the season reduces the natural shedding, and picking off any obviously damaged fruit as the season progresses will also help, but not eliminate the problem entirely. If a fruit is scarred or misshapen this will only grow with the fruit, so one might as well remove it and save the tree from wasting resources trying to get it to maturity. Infected fruits should be properly disposed of so that they do not create a source of infection. For information on thinning: http://homeorchard.ucanr.edu/The_Big_Picture/Fruit_Thinning/
Generally speaking, if the tree looks healthy and has a heavy crop of fruit falling in mid-summer should not be cause for concern.