Polysorbates as potential apple thinning agents

There is no perfect thinning agent in apple fruit production and in recent decades some thinning agents have lost the registration because of environmental reasons.
In the meantime, scientists have tested a wide range of substances for their potential flower and fruitlet thinning effect to meet the needs of commercial apple production.
Most of these substances function as flower caustic thinners, but apple growers prefer to use later fruitlet thinners where a shortage of reliable agents stays prevalent.
In this paper, a find of a strong fruitlet thinning action of polysorbates (20, 60 and 80) applied as late apple thinning agents is reported.
Polysorbates thinning efficacy has been tested at different application patterns and times on cultivars ‘Gala’, ‘Golden Delicious’, ‘Elstar’ and ‘Idared’. Polysorbates proved to be efficient thinning agents for all cultivars when applied twice in a later thinning window of fruitlets diameter above 9 mm.
The strongest thinning was observed on ‘Gala’ trees sprayed with polysorbates at 14 and 19 mm of fruitlet diameter.
On ‘Golden Delicious’ unacceptable levels of fruit skin russet were noticed, while on other cultivars russet does not seem to be a problem.
With some additional research effective polysorbate thinning programs could be developed for cultivars that are not too sensitive to fruit russet.
The possible introduction of polysorbates as late thinning agents in commercial apple production is discussed with regard to their accessibility and possible easy registration as “basic substances”.

IV International Symposium on Horticulture in Europe – SHE2021

M. Stopar, J. Hladnik

emulsifiers, late thinning, russet, polysorbate 20/60/80, fruitlet thinning, apple trees

https://doi.org/10.17660/ActaHortic.2021.1327.90