The inhibition of flowering by means of gibberellic acid application reduces the cost of hand thinning in Japanese plums (Prunus salicina Lindl.)

The application of gibberellic acid during flower bud induction significantly reduced flowering of ‘Black Diamond’ and ‘Black Gold’ Japanese plums. The response depended on the concentration applied and on the type of shoot. Mixed shoots had a similar response in both varieties, flowering being reduced by 40% for GA3 50 mg l−1 and by 75–90% for GA3 75 mg l−1 or higher concentration. With regard to spurs, GA3 50 mg l−1 reduced flowering intensity by 40% and 25% in ‘Black Gold’ and ‘Black Diamond’, respectively, and GA3 75 mg l−1 or higher concentration reduced flowering by 70% and 50%, respectively. This partial inhibition of flowering significantly reduced the cost of manual thinning. The best GA3 concentration was found to be 50 mg l−1, since it reduced the cost of thinning by 45–47% and increased final fruit weight by 7–33% for ‘Black Diamond’ and ‘Black Gold’, respectively. Not significant differences in yield and in mature fruit characteristics of treated trees were found compared to untreated trees.