Now is the time to THIN FRUIT on your trees. By late June they should have shed poorly pollinated fruits. This is known as the ‘June drop’. What remain will remain on the trees to ripen. It is nature’s way for the trees to retain what they can maintain.
What remain may well benefit from extra space to develop into with still some time before ripening. Thin apples to 1 or 2 per cluster. Give culinary apples even more space. One benefit from doing this is that the branches will not be weighed down too much. This seems to apply to plums in particular. Use finger & thumb or a pair of scissors / secateurs.
A major advantage of thinning is that it helps trees not overcrop. Heavy cropping one year can mean light or no crops the following year. Another advantage, with Plums in particular, is hygiene. Air circulation is improved, less contact between each plum reducing the spread of fruit rot as ripening gets closer.
When thinning apples try to remove any ‘KING’ FRUIT. These are usually fruit in the middle of any clusters. They can be recognised as often being larger than those around, can be mis-.shapened and have fatter stalks as in the picture. 
