Current thinking suggests that fruit abscission may be due to a temporary carbohydrate shortage. Cloudy weather and cool temperatures result in lower photosynthesis rates and less carbohydrate production. The use of Sevin, as a petal fall or first cover insecticide, can also act as a thinning with its effect variable between varieties. From a fertility standpoint, low levels of nitrogen can cause heavy June drop, especially in young trees. High nitrogen levels may also adversely affect fruit set.
Growers sometimes judge the degree of drop by what they find on the ground.
Rather, they should examine the tree closely to determine the set remaining. Even commercial growers are occasionally pleasantly surprised at harvest by the number and size of apple fruit, having believed that the crop would be light based on the June drop. This can happen especially when the trees exhibit heavy foliage. The Ohio Department of Agriculture began a series of steps in April 1999 to stop a virulent new tropical pest, the small hive beetle, from destroying honeybee colonies in Ohio. The beetle has the ability to destroy a bee colony within a matter of weeks.