Polysorbates 20, 60 and 80 are apple thinning agents
Chemical thinning of fruitlets is the most commonly used measure to improve fruit size and prevent biennial bearing in commercial apple production. There is no perfect apple thinning agent on the market and search for reliable thinning agents that would be environmentally and toxicologically unquestionable is ongoing. Thinning action of polysorbates 20, 60 and 80 was studied when used in the late application windows. Five mL L‑1 of each polysorbate or lecithin was applied twice: at 12.5+18, and at 18+20 mm of fruitlet diameter on cultivars Golden Delicious, Elstar and Fuji. Application of polysorbates 20, 60 and 80 induced fruitlets thinning in most timing of applications and apple cultivars. Fuji was most responsive to thinning with polysorbates and significantly responded in all treatments. On Golden Delicious three out of seven polysorbates applications proved significant thinning effect while other treatments showed only non-significant thinning action. Elstar significantly responded to the thinning with polysorbates in four out of seven treatments. All emulsifier applications significantly increased fruit skin russeting on Golden Delicious, but only a slight non-significant russeting was observed on Fuji and Elstar. Polysorbate applications did not influence return bloom. Polysorbates seem to be promising apple fruitlet thinning agents for late (rescue) thinning options.
Stopar, M. and Hladnik, J. (2020). Polysorbates 20, 60 and 80 are apple thinning agents. Acta Hortic. 1295, 57-62
late thinning, apple trees, emulsifiers, polysorbates