Who causes premature dropping of plum fruits?

Plum trees bloom profusely, but from May until harvest there are periods of premature shedding of fruit set and fruits, which significantly reduces yields. If the causes of this are known, some of them could be prevented.

• The young fruit set shed soon after flowering. Cause – lack of seed due to improper fertilization or degeneration of ovules.
• The young fruits shed (June drop) – from the second half of May to the first half of July. Cause – insufficient accumulation of assimilates in the plants during the preceding year and water deficit.
• The fruits shed with their stalks, have two holes and a smell of house bug. Shedding begins in May and ends in early June. Cause – black plum fruit sawfly and yellow plum fruit sawfly.
• The fruits shed during the second half of June and the beginning of July. In the seed of the shed fruits there is a whitish larva with a brown head, without legs and with a body tapered at both ends. Cause – seed-feeding insects of the genus Eurytoma.
• Pre-harvest fruit drop. Cause – disturbed balance between auxins and ethylene.