In three seasons from 1962 to 1964, effect of Peach-thin spray was tested on peach flowers in their different stages of development. Tested flowers wers selected to be in almost the same stage by removing flowers in earlier or later stages.
In 1965 and 1966 comparison tests were conducted between morning and mid-day sprays.
1. In 1962, 200 and 800ppm solutions were applied on the flowers in four stages on four Hakuho trees, which were thirteen years old and moderately vigorous. Thinning effect was lowest on flower buds before blooming, high on blooming flowers, and a little less on the flowers five days after blooming than on blooming flowers. Sprays ten days after blooming resulted in heavy thinning. Effect of 800ppm sprays was found to be too severe except on flower buds. Foliar epinasty was observed in the treatments of 200ppm spray in lates and all treatments of 800ppm spray.
2. In 1963, the same trees as in the previous season were used, and 200ppm Peach-thin was applied. Fruit set reduction was almost equal by the sprays at the day of blooming, 2 and 10 days after blooming, while effect was less by the spray 6 days after blooming.
3. In 1964, 200ppm solution was applied on the same trees used in the previous season. Thinning effect was highest by the spray 4 days after blooming and was followed by the sprays 7 and 11 days after blooming in the order.
4. Three season′s tests seem to show that the thinning effect of spray at the day of blooming is almost the same as that 2 days after blooming, and it becomes to be less as the date of spray is delayed, while it is quite variable by the sprays 10-11 days after blooming.
5. Morning and mid-day sprays were compared in their thinning effect on 8 years old Hakuho, 7 years old Okubo, and 4 years old Re-13 trees. Morning spray thinned more than mid-day spray on Okubo. On Hakuho and Re-13 trees, however, differences in fruit set reduction between morning and mid-day spray were not significant.