Pg. 5-10 The Long-term Effect of Growth Regulators and Pruning on the Size, Yield and Fruit Quality of Litchi Trees

Methods to control the size of adult litchi trees were investigated at Friedenheim (25°S) over a five-year-period. The treatments consisted of pruning fruit-bearing branches by 30 cm at harvest; applying foliar sprays of paclobutrazol (PP333} onto postharvest flush and young flower panicles; drenching soil with PP333 and a combination of pruning and
soil applications with PP333 and Chlormequat-chloride (CCC) sprays of post-harvest flush and young flower panicles. Annual yields and fruit quality were recorded. Residue analysis of PP333. in fruit was also determined. Tree height and canopy diameter of trees of the different treatments were measured before commencement, during and after termination of the project. 

Effective size control and manipulation of litchi trees were achieved by means of pruning, soil application of PP333 and a combination of these two treatments. These treatments, however, require more intensive and higher inputs. Higher yields are therefore required to economically justify their use, but this was not always achieved and a wider variation in yield occurred than in control trees. There was as much variation in fruit quality from season to season as yield, which made interpretation of results in this case difficult. Residues were present in fruit of the trees that were treated with PP333. The detection of traces of PP333 residues mitigated against a recommendation for its use on a commercial scale, particularly if the crop is to be exported.

Pruning of bearing branches can be recommended as a method of tree size control. It controlled tree growth without affecting yield significantly, in the long run, while being an environmentally friendly manipulation technique. CCC cannot be recommended from the results of this study. Yields over the five seasons of this trial were not improved substantially, and probably not economically, if used in conventionally spaced orchards.

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