Evaluation of different bud break promoters on 'Williams' (Pyrus communis L.) pear

'Williams' is the most cultivated pear in Uruguay and requires more than 900 chill hours to exit from the endodormancy. When this condition is not satisfied, the application of budbreak promoters is necessary to facilitate the bud swelling. The experiments were carried out in a pear orchard of 'Williams' (Pyrus communis L.) located in the Experimental Station INIA Las Brujas, during the 2017-2018 season. The objective of the study was to evaluate the effect of budbreak promoter applications on budbreak. Two experiments were performed: Experiment 1 consisted in the application of Erger^® 4%, Erger^® 2% and mineral oil 4%, in two dates: August 15, 2017 and September 1, 2017. Experiment 2 consisted in the application of Erger^® 8% and hydrogen cyanamide 1% on August 15, 2017 and Erger^® 4% on September 28, 2017. In 2017 chill units in Uruguay were 187, while the average for the last 20 years is 843. Thus chill requirements of 'Williams' pears were not met. Because of the inadequate chill accumulation (32% of the chill units NDASH CU or 78% of the total chill portions NDASH CP), no difference was observed in the final budbreak among the treatments, and the budbreak percentage never exceeded 20% for any treatment. Analyzing the budbreak discriminated per type of shoot (vegetative spurs, reproductive spurs and one-year shoots), no significant differences were observed among the treatments except for vegetative buds in experiment 1, where the treatments with mineral oil achieved a higher final budbreak (20%).