S16 - Session P1 - Crop load management on apples: alternatives to carbaryl and an organic thinning option on the Uruguay conditions

Authors: Bruno Carra *, Poliana Francescatto, Pablo B. Rodríguez, Danilo Cabrera, Marcelo Falero, Maximiliano Dini

Apple trees set many more fruit than desired, requiring a crop load adjustment to avoid biennial bearing. Thus, the aim of this study was to evaluate the effect of different plant growth regulators as 6-benzyladenine (6-BA) and naphthaleneacetic acid (NAA) sprays and lime sulfur (LS) in apple thinning. Two trials were carried out in Uruguay on 2020/2021 and 2021/2022 growing seasons in ´Gala Baigent´ and ´Rosy Glow´ apples, respectively. Productive and quality parameters were evaluated. LS (3%) sprayed three times near the bloom and the different combination of 6-BA (100mg L -1 ) + NAA (10mg L -1 ) showed positive results reducing the number of thinned fruit and time of hand thinning compared to control trees in ´Gala Baigent´ in 2020/2021 growing season, but 6-BA sprayed alone once at 10-12mm stage did not. LS (3%) and the combination of 6-BA + NAA increased fruit weight of ´Gala Baigent´ and did not significantly reduce yield on 2020/2021 growing season. For ´Rosy Glow´ apples, LS sprayed three times reduced the number of thinned fruit and time of hand thinning compared to control. 6-BA sprayed alone at 8-12mm did not reduce thinning time and number of thinned fruits as for ´Gala Baigent´. Fruit weight of ´Rosy Glow´ apples was not increased by LS, however, NAA (20mg L -1 ) alone or the combination of 6-BA (100mg L -1 ) + NAA (10mg L -1 ) at petal fall increased fruit weight compared to untreated control trees. Collectively, the results of the last two seasons are promising and indicate all the thinners used are potential tools on a chemical thinning program for apples to replace carbaryl. Furthermore, LS could be an option for growers in a thinning program, including for organic production.