IMPROVED FRUIT SETTING WITH PLANT GROWTH HORMONES

The use of a three hormone mixture to set unpollinated flowers of the apple cv., Cox’s Orange Pippin, was reported at an earlier Symposium (1972). Further progress in the technique is described.

Areas of commercial Cox orchards, sprayed at petal fall with a mixture containing gibberellic acid (GA₃), NN’-diphenylurea (DPU) and 2-naphthoxyacetic acid (NOXA) have yielded up to 38% more fruit than unsprayed areas, though the response has been variable.

Later application of the same mixture a week before ‘June drop’, resulted in increased fruit size and fruit retention in a tree unit experiment, and in increased yield in a commercial trial.

Though GA₃ or GA₄₊₇ alone, or in combination with NOXA, set muslin-enclosed Cox flowers, mixtures of gibberellin, DPU and NOXA gave the highest sets.

Analysis of sprayed fruit showed that the residue of DPU declined approximately exponentially with time, and at harvest no DPU was detected.

Flower ‘quality’ and the degree of competition from seeded fruit have both been found to affect hormone-induced set.
It is suggested that these two factors are primarily responsible for the varying response to the hormone mixture.

Symposium on Growth Regulators in Fruit Production

G.K. Goldwin

https://doi.org/10.17660/ActaHortic.1978.80.16