Peach and apple thinning by shading and photosynthetic inhibition

Abstract

SummaryShading cv Biscoe peach scaffold limbs 30–40, 35–45 and 40–50 days after full bloom (AFB) caused greater fruit abscission than shading from 15–25, 20–30, 25–35 or 50–60 days AFB. Terbacil, applied to peach limbs at 400 ppm thinned fruit at a similar timing as shading (35 and 40 days AFB). Whole tree airblast sprays of terbacil (300 ppm) applied 35 days AFB to cv Redhaven peach trees induced fruit abscission, but c. 25 % of the leaves showed marginal yellowing at harvest. Flower buds were produced at the nodes of leaves bearing symptoms. Shading of cv Starkrimson Delicious limbs from 16–26 days AFB caused significant fruit abscission. Shading 6–16, 26–36 and 36–46 days AFB did not induce fruit drop. Terbacil (400 ppm) applied to limbs at 6 and 16 days AFB significantly reduced fruit set, but applications 26 and 36 days AFB were ineffective. Whole tree airblast applications of terbacil (200 ppm) defruited spur cv Delicious trees when applied 16 days AFB. Limb treatments of terbacil at rates twice those of the airblast treatments caused much less fruit abscission. No leaf symptoms were observed with the airblast treatments (200 ppm), but some yellowing of leaves occurred on the limb treatments that were applied with a hand sprayer to the point of drip at 400 ppm. Apple and peach fruit from shaded or terbacil-thinned limbs or trees were similar or larger than from hand thinned.