Benefits of chemical thinning
Benefits of chemical thinning
All chemical thinners have some disadvantages, however, despite these limitations, a chemical thinning program produces markedly superior results to hand thinning—both economically and in terms of tree physiology.
The most effective chemical thinning programs combine blossom and post-bloom thinners. A sequential spray program allows lower quantities of chemical to be used at each timing, thus reducing the risk of over thinning.
If the chemical thinners have been effective then all that should be required is a subsequent light hand thin to remove damaged fruit or break up any remaining bunches.
To achieve good thinning and fruit quality, all chemical thinners need to be applied at the appropriate physiological stage and under the climatic conditions which are best suited to each chemical.
Research work has shown that the addition of a non-ionic surfactant such as Kendene (Tween 20) enhances the effect of all thinners, except for carbaryl/thiram.
Choice of thinning chemical is important as some cultivars do not respond well to some chemicals. The currently recommended chemical/cultivar combinations are shown in Table 2.
Economics of thinning
Economics strongly favour an aggressive thinning approach based on knowledge and records.
Under-thinning is costly, resulting in small fruit size, poor fruit quality, extensive hand-thinning and inadequate flower bud initiation for next year.
Over-thinning is not a common occurrence— even with an aggressive approach. If it does occur, there will be no hand thinning expenses, fruit quality is normally high and return bloom the next year is assured. Under-thinning has no such bonuses!
How do I thin my crop?
There is no simple answer to the question "How do I thin my crop?" The two most important factors are application timing, and ensuring that conditions are suitable for the particular chemical at time of spray application.
Discuss possible strategies with your neighbours and local grower group. If you have a program that works, stick to it!
Future directions—a new tool to replace chemical thinning
Crop load management is the single most important practice determining the annual profitability of apple orchards, yet it is the most difficult.
While our knowledge of chemical thinning and tree response has come a long way over the last 25 years, using chemicals to control crop load will always remain unpredictable. Hence we need to look for other ways to manage crop load.
As early as 1995, Pierre-Éric Lauri and his research group studied the difference between regular and biennial bearing cultivars, and observed that regular bearers have high natural spur extinction.
The New Zealand research group led by Dr Stuart Tustin has followed up on these studies and further developed the concept of Artificial Spur Extinction (ASE) for management of crop load.
Comparing ASE with conventional pruning management
As part of the national HAL funded PIPS (Productivity, Irrigation, Pests and Soils) Tree Structure program, field trials duplicated in Tasmania, Victoria and Queensland have been comparing the impact of ASE with conventional pruning management on fruit set response, yield and fruit quality.
The project team* is in the process of summarising the data from this exciting project. Results indicate the potential of ASE to supersede and eliminate the present requirements for chemical thinning to regulate biennial bearing and crop loading.
This exciting work is likely to result in a shift in contemporary orchard system production approaches and technologies.
Further information on this work can be found in the May and June editions of Australian Fruit Grower Magazine.
*The project team: Dr Stuart Tustin, Dr Ben van Hooijdonk, Ken Breen (PFR NZ); Dr Simon Middleton, Dr John Wilkie, Dr Heidi Parkes (DAFF Queensland); Dr Dugald Close, Dr Sally Bound (TIA, Tasmania)
For more information, see Tree Fruit October 2014
