Early fall defoliation reduces yield and bud nutrient concentration in 'Selah' sweet cherry

The effect of early defoliation on buds and tissue nutrient concentration and fruit yield was evaluated during 2018 and 2019 on 'Selah' sweet cherry (Prunus avium L.) at Washington State University research station in Prosser, WA. Early defoliation was done by hand (HD) by removing all the leaves from the tree, or by chemical spray (CS) with 2% urea plus 2% zinc sulfate. Each treatment was applied on different dates, approximately at 70, 60 or 50 days before natural leaf fall (BNLF). In both years, chemical defoliation did not induce complete leaf drop, but leaf senescence was advanced. Early HD 70 and 60 BNLF reduced N concentration on buds and yield, only in 2019. Early defoliation 70 DBLF, by hand or with chemical strays, and HD 60 reduced Zn levels in buds in 2019. However, none of the treatments affected leaf nutrient concentration after harvest. The CS defoliation with 2% urea and 2% Zn sulfate did not affect yield, leaf nutrient concentration or N bud nutrient levels. However, in 2019, the earliest CS reduced while the later CS increased Zn concentration in buds. Early HD 70 and 60 BNLF reduced yields only after two consecutive years, however, chemical foliation utilizing 2% urea plus 2% Zn sulfate applied 60 to 50 BNLF was effective in accelerating leaf drop, with no negative effect on yield or nutrient levels the following season.