The efficacy of 1-aminocyclopropane-1-carboxylic acid (ACC) in thinning 'Keisie' peaches

Annual cropping is very important in any deciduous fruit industry and it is believed that annual cropping can be achieved through optimizing thinning practices. Currently peaches are mostly thinned by hand, but there is a great need for chemical thinning strategies in the peach industry. The purpose of this study was to evaluate new thinning strategies on 'Keisie' peaches. 1-aminocyclopropane-1-carboxylic acid (ACC) and 6-benzyladenine (6-BA) were evaluated as foliar applications made when the average fruitlet diameter was 8-10 mm during two seasons. There was a significant thinning effect on 'Keisie' in two seasons with ACC and 6-BA. ACC reduced fruit set linearly as the ACC rate increased. No reduction in yield was observed in both seasons and fruit size was not affected. Based on two season's data, the recommended rate of ACC for 'Keisie' would be 400 mu L L-1 at 8-10 mm fruitlet diameter. During a third season, ACC was evaluated at two stages of fruit development, 4-6 and 8-10 mm diameter. Again a linear increase in thinning efficacy was found with increasing ACC rate. At one site the later applications were more effective, but at the second site the difference was not significant. No split pit was recorded, but slight leaf drop was observed in 'Keisie'. Based on what we found in the two seasons, ACC seems very promising as a potential thinning product on peaches, but 6-BA would not be recommended to be used as a chemical thinner for peaches.