J. Vercammen, A. Gomand, D. Bylemans
A good harvest is, amongst others, based on a good fruit set. Indeed, even if there are less flower buds, a reasonable harvest can still be obtained as long as a maximal fruit set can be realized. In years with a smaller amount of flower buds, growers often explore all possibilities to obtain a good fruit set by using various plant growth regulators and by using the highest dose rate registered. For example, in practice high doses of gibberellins are often applied to solve this problem, but the outcome is not always positive as fruit shape and flower bud formation might be negatively impacted.
After gibberellin application an initial increase in fruit set can be noticed, but most of the effect is often lost at June drop. Our research demonstrates that this June drop can be reduced when prohexadion-Ca (Regalis) is applied 2 to 3 weeks after full bloom. This plant growth regulator, on the market from 2002, was applied for its properties to inhibit shoot growth. But besides an effect on shoot vigour, pro-hexadione-Ca also reduces the production of ethylene, which finally results in a reduced fruit drop in June.
Regarding fruit set treatments on ‘Conference’, a low number of flower buds and the appearance of frost damage are the main triggers to apply plant growth regulators (PGRs). The decision to apply PGRs has to be adapted to each particular situation.
Vercammen, J., Gomand, A. and Bylemans, D. (2015). IMPROVING THE FRUIT SET OF 'CONFERENCE' WITH GIBBERELLINS OR REGALIS. Acta Hortic. 1094, 257-264
DOI: 10.17660/ActaHortic.2015.1094.32
fruit set, GA3, GA4/7, June drop, Prohexadion-Ca and anti-ethylene effect

Acta Horticulturae