Dormancy-breaking inducers on apple cultivars grafted onto Geneva® rootstocks in subtropical region of Brazil

•Erger® was as efficient in budburst percentage as H2CN2.•Bluprins® showed superior efficiency in budburst performance compared to H2CN2.•All concentrations of Bluprins® showed a higher percentage of fruit set.•Erger® and Bluprins® were efficient in budburst and fruit set percentage. Budburst require a certain number of chill hours (CHs), known as a chilling requirement, to break endodormancy in temperate fruit trees. This step is crucial for proper flowering and fruit set, as incomplete fulfillment of the CHs leads to asynchronous flowering, resulting in low-quality flowers and fruit set. One of the first and most efficient agrochemicals used for this purpose is hydrogen cyanamide (H2CN2). However, some studies have raised concerns about its toxicity. Therefore, other non-toxic agrochemicals have been employed as alternatives. This study evaluated the effects of different budburst inducers Bluprins® (0.7 % free amino acids + 4 % nitric nitrogen + 4 % ammoniacal nitrogen + 5.5 % organic carbon), Erger® (3.1 % ammoniacal nitrogen + 5.8 % nitrate nitrogen + 6.1 % urea nitrogen + 3.3 % calcium), Droop® (42.4 % thidiazuron), and Dormex® (0.5 %–1.0 % H2CN2) at varied concentrations on the ‘Galaxy’ and ‘Mishima’ apple trees grafted onto Geneva® Series G.210 or G.814 rootstocks. The study was conducted during the mild winter conditions of Southern Brazil during the 2020–2021 and 2021–2022 growing seasons. These budburst inducers were applied when 400 CHs were