1. The occurrence rate of sun scald on plum fruits according to the various treatments was lowest by paper bagging of the fruits, lower by spraying lime in 20 days before harvesting, low by irrigation especially accompanied by grass mulching, but little effective by boron application in comparison with the cheek plot of no treatment.
2. The highest rate of sun scald on the fruits appeared on the third day after beginning of harvest.
3. The branches grown toward the South-West, the East, and the South showed more serious damage of sun scald on the fruits compared with those grown toward the other directions.
4. The acetealdehyde content in damaged fruits was 2.5 times as much as that in normal fruits.
5. With increasing temperature sun scald appeared more and rapidly in a short time.
6. It is considered that sun scald on the fruits is caused by disturbance of hidrometablism, sunlight, high temperature and accumulation of acetealdehyde.
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