DESICCATING CHEMICALS FOR BLOOM THINNING OF PEACH AND PHOTOSYNTHETIC INHIBITION FOR POST-BLOOM THINNING OF APPLE AND PEACH

Airblast application of fertilizers, desiccant herbicides, or surfactants reduced fruit set and increased fruit size of "Redhaven" peach (Prunus persica (L.) Batsch). The addition of a surfactant to ammonium thiosulfate (ATS) at rates from 0 ml/1 to 5 ml/1 did not improve the thinning response.
At constant rates of ATS/ha water volumes from 2,338 1/ha to 420 1/ha gave no difference in thinning.
Forty-six percent more flower buds developed on twigs from bloom-thinned trees than from hand-thinned trees.
Most of the additional flower buds were on the basipetal 5 nodes of current season shoots.
Treatment of the stigma, petals + anthers, peduncle, or calyx with ATS reduced fruit set.
Microscopic examination of flower buds from several spray treatments 48 hours after treatment revealed necrotic regions in the peduncle of some flowers.
Flowers sprayed with DuPont WK or NH4NO3 + X-77 plus methylene blue (added as a tracer) showed, upon microscopic examination, presence of the blue dye in the calyx, pedicle and peduncle veins of some flowers after 24 hours.

Shading of "Biscoe" peach scaffold limbs from 30–40, 35–45, and 40–50 days after full bloom caused greater fruit abscission than shading from 15–25, 20–30, 25–35, or 50–60 days after full bloom.
The photosynthetic inhibitor, 3-tert-butyl-5-chloro-6 methyluracil (terbacil, 400 ppm) applied to peach limbs thinned fruit at a similar timing as shading (35 and 40 days after full bloom). Whole-tree airblast sprays of terbacil (300 ppm) applied to "Redhaven" peach trees 35 days after full bloom induced fruit abscission, but approximately 25% of the leaves showed marginal yellowing at harvest.
Flower buds were produced at nodes of leaves bearing symptoms.

Shading of "Starkrimson Delicious" limbs from 16–26 days after bloom caused significant fruit abscission.
Shading 6–16, 26–36, or 36–46 days after full bloom did not significantly affect fruit set.
Terbacil (400 ppm) applied to limbs at 6 or 16 days after bloom significantly reduced fruit set, but later applications (26 or 36 days after bloom) were ineffective.
Whole tree airblast applications of terbacil (200 ppm) defruited spur "Delicious" trees when applied 16 days after full bloom.
No leaf symptoms were observed with the airblast treatments.
Apple and peach fruit from shaded or terbacil thinned limbs or trees were similar or larger than those from hand thinned trees.

V International Symposium on Growth Regulators in Fruit Production

R.E. Byers, C.G. Lyons Jr, J.A. Barden, R.W. Young

https://doi.org/10.17660/ActaHortic.1986.179.111