RESPONSE OF PEACH TREES TO BLOOM THINNING

Bloom thinning peach trees resulted in a 20–30% increase in fruit size when compared to hand thinning 40–50 days after bloom.
Bloom thinned trees were found to have more fruiting wood and greater numbers of flower buds per unit length, particularly on the basal 5 nodes.
Bloom thinning by cutting the stigma off in the pink or early bloom stage interfered with pollination and fertilization of the ovule causing fruit to abscise before and during "June drop" (40–60 days after bloom on ‘Biscoe’ cultivar) in a way similar to chemical thinning with the ammonium thiosulfate fertilizer (12–0–0–26). Fruit with unfertilized ovules were impossible to distinguish from fruit with fertilized ovules at 25–30 days after full bloom.
Early hand thinning (if done at 25 DAFB) was difficult to assess since unfertilized ovules could not be distinguished from fertilized ovules.

The increased flower bud production caused by bloom thinning was offset by the application of GA3. Applications made 47 days after bloom reduced flower bud numbers 2X on shoots 45–70 cm in length but 4X on shoots 10–30 cm in length.
Application of GA3 appeared to distribute the flower buds better by reducing flower numbers on the basal sections of shoots and on shorter smaller wood where smaller fruit are borne.
Applications made earlier allowed more buds to develop.
The optimum time for this treatment would depend on cultivar and crop load.

II International Peach Symposium

R.E. Byers

https://doi.org/10.17660/ActaHortic.1989.254.18