Irrigation water supply can often be less than crop water requirement during a drought—this leads to tree water stress and subsequent loss in fruit size and yield in apple orchards.
Fruit thinning strategies (Continued from last issue)
Thin early in the season
Thinning early in the season is recommended.
Base the level of thinning on fruit set and the outlook for irrigation water allocations.
Regularly review irrigation strategies for different cultivars when low allocations are expected.
A further follow-up thinning may be needed, although the longer thinning is delayed the smaller the fruit will be at harvest.
There are two reasons for this.
Firstly, cell division dominates fruit growth at the start of the season. Any restriction on cell division cannot be regained later in the season. Conditions must be favourable for cell division so any competition between fruits needs to be minimal.
Secondly, dry weight accumulates in developing fruits but there is a limited total pool of dry weight to go around.
Too many fruits means that the tree can only supply each fruit with a limited amount of dry weight.
At the start of the season there is usually enough dry weight for all the fruit. However, as fruit grows its demand for dry weight increases rapidly.
Thinning well-before the demand by the fruit exceeds the supply available from the tree is critical to maximise final fruit size.
Contact Ian Goodwin, Research Leader, Tatura, phone 03 5833 5240
See this article in Tree Fruit Dec 2019
