Fruit set of ‘Jonagold’: a small dose of gibberellins or Regalis

A treatment with a low dose of GA₄₊₇ can improve fruit set.
After bloom an initial increase in fruit set can be observed after a treatment with GA₄₊₇, but often this is lost for the most part during June drop.
To counter this heavy June drop even Regalis (Prohexadion-Ca) was tested to reduce the competition between fruits or between vegetative and generative growth.
Regalis inhibits gibberellin formation, but acts also as an anti-ethylene agent when it is sprayed between 2 and 4 weeks after full bloom.
Regalis can reduce June drop, but the timing of spraying is important and the effect is only short lasting (4 to 5 days). Therefore we recommend to spray 2 times at a rate of 0.5 kg ha^-1 2 and 3 weeks after full bloom.
The treatments must be done before the occurrence of stress.
Stress can be caused by dryness, insufficient radiation (= 2 to 3 dark days), general poor weather conditions and other factors.
On parcels in an off-year or after frost damage, it is also possible to spray twice with 0.5 or 1 kg ha^-1 of Regalis at the beginning of bloom and 3 weeks after full bloom to reduce shoot growth, so there is less competition for nutrients.
Between beginning of bloom and full bloom one must also spray 5 g GA₄₊₇ ha^-1, leaving at least 3 days between spraying this treatment and the one with Regalis.

III Balkan Symposium on Fruit Growing

J. Vercammen, A. Gomand, V. Siongers, D. Bylemans

GA₄₊₇, prohexadion-Ca, anti-ethylene agent, June drop

https://doi.org/10.17660/ActaHortic.2016.1139.75