Volume 70 Number 4 Article 1 Pages: 172-179
Year 2016 Month 10
Title: Effects of Ethephon as a Blossom and Fruitlet Thinner on Yield and Fruit Quality of 'Jubileum' European Plum in a Nordic Climate
Authors: Mekjell Meland and Clive Kaiser
European plum cultivar Jubileum (Prunus domestica L.) blooms abundantly most years and too many fruit can be set if flowers and/or fruitlets are not properly thinned.
In 2007, 2008 and 2009, mature 'Jubileum/St.
A' trees were treated with ethephon either at full bloom, at concentrations of 250, 375 and 500 mg/L or when
fruitlets averaged ~12 mm in diameter at concentrations of 125, 250 and 375 mg/L. In general, flower-thinning
treatments reduced fruit set significantly.
Fruit set decreased with increasing ethephon concentrations, and the
highest rate of ethephon applied either at full bloom (500 mg/L) or post bloom (375 mg/L) resulted in excessive
Up to 375 mg/L of ethephon was required at full bloom whereas only 125 mg/L of ethephon was
required post bloom for marked fruitlet thinning.
Yields confirmed the fruit set response and yield reductions
In most years, all thinning treatments resulted in fruit larger than 38 mm in diameter compared
to fruit from unthinned control trees.
Fruit quality, characterized by blue surface color and soluble solids content
was generally higher and increased significantly with the reduction in crop load.
Fruit firmness of fruit from all
ethephon applications was lower than that of the fruit from unthinned control trees.
In contrast, titratable acidity
did not show a clear response to ethephon thinning.
Return bloom the following year was mostly unaffected by
all ethephon applications compared to the control.
In conclusion, an ethephon application at a rate of up to 375
mg/L applied at full bloom will result in adequate thinning of 'Jubileum' plums and achieved a target of about 10-15% reduction in fruit set.
When weather conditions are not conducive during flowering, a post bloom ethephon
application at 125 mg/L may be applied however, this should only be considered in years of excessive flowering and as a last resort.
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