Modelling Biennial Bearing in Apple Trees

Abstract

Many commercially grown apple cultivars have a biennial cropping habit, producing many small fruit in one year and few or none in the following year. The production of fruits is known to inhibit flower initiation for the following year. This undesirable trait is frequently managed by removing (thinning) some flowers or young fruit in years of heavy flowering which improves the size of remaining fruits, but does not reliably improve flowering in the following year. The effect of thinning on flower initiation is not well understood. Two mathematical models are developed describing the relationship between flowering in one year and the next. The first models the effects of thinning on return bloom and attempts to define maximum repeatable flower number. The second models how proximity of growing points may impact biennial bearing and maximum annual flower number. This second model may be useful to advance research into biennial bearing in apple.