Why is early crop load management so important?
The natural fruit drop observed in fruit trees, particularly apples, in early summer is insufficient to achieve optimum crop loads, fruit size and quality, or to prevent biennial bearing.
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As discussed earlier, flower initiation for the following year begins shortly after fruit set and trees carrying heavy crop loads over this period will have reduced flower buds the following spring.
Hence, to ensure regular bearing and optimise fruit quality, we need to manage our crop loads early in the season—in an on-year this means removing over 90% of the potential fruitlets within six weeks of bloom.
It should be noted that trees that are not carrying excessive crop loads tend to have a very small, or no, natural fruit drop.
Critical: first six weeks after flowering
The first six weeks after flowering is also when cell division occurs in the developing fruitlets, and maximising resources during this period of fruit growth will maximise both fruit size and internal quality.
Leaving excess fruit on the tree during this period is a waste of the tree’s resources, as growth is put into fruit that later drops or is removed.
The negative relationship between crop load and fruit size is well known, but high crop loads can also have a negative effect on fruit firmness and sugar content.
Hence, it is more productive to channel this energy into fruit that will remain on the tree through to harvest. This is particularly important in drought years when water resources are scarce.
Tools for managing crop load
Crop load has been managed over the last 25–30 years by pruning and chemical thinning, followed up with hand-thinning.
We are fairly lucky in Australia with a choice of chemicals available. While our knowledge of chemical thinning and tree response has come a long way over the past 25 years, juggling application of chemical thinning agents with unstable spring weather conditions is a fine balancing act; using chemicals to control crop load is always likely to be unpredictable.
(cont next issue)
Download the Orchard plant protection guide
See this article in Tree Fruit July 2020
