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Who is the report targeted at?
The report is targeted at members of the relevant industry associations and associated State or Federal Government research and extension personnel.

Background
The longan industry is mostly located along the east coast of Queensland with minor planting’s in northern NSW. Current longan plantings are reported to be in the vicinity of 70,000 trees and the annual production of 1000 plus tonnes are valued at $5.0M. Approximately 80% of the industry is located on the Atherton Tablelands Region of far north Queensland.

The rambutan industry is confined to the wet tropical coast of far north Queensland and the rural area around Darwin in the NT. The bulk of the industry (22,000 trees, 75%) is situated in north Queensland with the value of production estimated at $4.3 M.

The variable and unpredictable nature of production in these crops has been a major hindrance in the development of the industries. Assured flowering, and cropping every season, would be of great economic benefit to the industries concerned and the north Queensland rural regions, where longan and rambutan are cultivated. Regular crop production would allow industries to plan their development and marketing strategies. These industries have included flowering management and tree size control as major production issues limiting industry development within their respective strategic plans. Industry planning officers believe that by 2010 the longan and rambutan industries could potentially be valued at $15M and $6M respectively.

Aims/Objectives
Maximise the production potential of longan and rambutan by improving consistency of flowering along with canopy height management
Examine the effects of a range of physical and chemical growth regulators on vegetative growth and flowering

Methods used
A series of experiments were undertaken to test the application of various pruning strategies and the effects of physical and chemical growth regulators on vegetative growth, flowering and subsequent fruit set. Field trials were conducted in North Queensland on government research stations and growers’ properties over four years. In longan, additional work was carried out to investigate crop thinning recommendations and crop forecasting guidelines. Whereas in rambutan, additional work included the examination of synthetic auxins to manipulate the sex ratio of flowers.

Results/Key findings
In relation to the objectives of the report In longans the results indicate similar responses to potassium chlorate (KCIO3) across cultivars, soil type and climates. On the first application a rate around 5-10g/m2 of the canopy spread reasonably evenly under the canopy and watered is suggested. While for foliar application, rates of 0.2% applied until runoff was found to be most effective. On repeat applications the ideal rate varies depending on whether the trees are in a conducive or non-conducive state to flower. In conducive trees (dormant mature vegetative growth, during normal flowering time) rates of 10g/m2 resulted in maximum flowering while in non conducive trees (active vegetative growth, young flush, out of season flowering) rates of 10-20g/m2 of the canopy are required and even then the flowering response is sometimes still poor. Similarly for the foliar applications, in conducive trees lower rates (0.5%) were required then in non-conducive trees (1%). The high rates required to achieve reasonable flowering in the non-conducive trees resulted in excessive leaf fall and therefore cannot be used.

Two factors identified in determining the success of KClO3 application in triggering good flowering on repeat applications were the level of flushing or stage of growth and the leaf nitrogen level in the trees at the time of application. It was found flowering was best when KClO3 was applied to trees which had dormant mature vegetative shoots and the longer the shoots have been mature the better, although some flowering can occur in shoots with active growth it is never as good. When trees are heavily pruned or during the hot wet summer months vegetative growth is strong and flushing tends not to mature and become dormant before flushing again, so achieving good flowering in these conditions is difficult. It can take up to 2 years for growth to stabilise after heavy pruning. Leaf nitrogen levels indicate that above 1.7% good flowering is generally difficult to achieve on repeat applications, while at levels below 1.2% good flowering is more easily achieved.

With increasing use of KClO3 longan trees are being cropped more heavily and consistently than ever before. Heavily bearing longan trees are very prone to overcropping resulting in small poor quality fruit and tree decline. Trials have indicated that trees are capable of supporting around 3-5kg of fruit/m2 of the canopy surface area. This usually requires that 40-60% of the crop load be removed from trees in full flower.

The ability of KClO3 to trigger out of season flowering allows growers to time the flowering and cropping of their trees. Trials have allowed the development of a predictive formulae using heat sums which has allowed growers to predict the crop harvest date from different application dates so that they can time their crops with market opportunities.

The root pruning and chemical growth retardant work demonstrated that vegetative growth could be reduced with the use of monthly sprays of foliar paclobutrazol (0.5%) either by itself or in combination with root pruning. Neither treatment improved flowering.

In rambutan research into pruning and manipulation of floral induction in rambutan suggest that there is no easy solution to managing pruning and subsequent flowering in the north Queensland growing environment. Unlike the use of KClO3 in longan there is no flowering ‘switch’ yet discovered for rambutan. This project has improved the understanding of the effects of pruning time on subsequent regrowth and flowering. Unfortunately none of the trialled pruning times significantly improved the chances of obtaining flowering and fruit set in the subsequent season. This leads to the conclusion that growers will need to consider staggering their heavy pruning operations through out the orchard if they wish to ensure some production in every year. The results clearly indicated that nearly two full seasons of growth was required before growing terminals were at a stage that flowering could occur.

None of the growth regulating techniques trialled significantly improved flowering yet there were indications that the physical growth regulating techniques (cincturing and root pruning) may warrant further investigation. Growth regulating chemicals other then those trialled should be tested as they become available.

Additional findings
In rambutan the use of synthetic auxins to manipulate the sex ratio of rambutan flowers did show strong promise. This technology could significantly improve the productivity of early flowering orchards. Further work will be required to confirm the efficacy of the technology as well as to seek product registration.

 Implications for relevant stakeholders for:

Industry
The project has developed a number of strategies and management options that longan and rambutan growers can use to maximise the production potential by improving consistency of flowering along with canopy height management. The strategies differ for each crop and further developments are envisaged as the outcomes of the work are fully incorporated into industry practice.

• Communities Both longan and rambutan are tropical fruits which require a high labour input during harvesting, packaging and marketing operations. Consistent and increased production leads to more efficient business operations. Ultimately more profitable industries lead to profitable communities via increased employment opportunities.
• Policy makers There are no direct implications to policy makers except the understanding that tropical horticulture industries such as the production of longan and rambutan are important part of horticulture production in northern Australia. Although these industries are small in their own right they contribute to the economic diversity of the horticulture industry and regional employment opportunities.

Recommendations
The recommendations below are targeted specifically at growers of the crops highlighted below:

• Longan Research work from this project has demonstrated that the chemical Potassium Chlorate (KClO3) is a powerful flowering inducing agent in longan trees (flowering occurring around 6-8 weeks after application). Ideal rates, timings and methods of application have been determined as well as guidelines for crop thinning and crop maturity forecasting. Controlling vegetative growth was unsuccessful using root pruning but foliar sprays with paclobutrazol did reduce vegetative growth.
• Rambutan Management of pruning still remains an important issue, particularly as there is a need to maintain tree height to a level which allows for economical picking and netting for crop protection purposes. Our studies suggest that trees require 16 months or more following heavy pruning to begin to flower and fruit with 21 to 25 months being necessary for the highest yields to occur. The earlier in the calendar year that pruning can take place the better. However, this may not always be possible because in most cases trees are still bearing fruit with harvest operations generally commencing from mid February.

The other alternative is for pruning to occur from August when warming spring temperatures allow the new post pruning flush to develop quickly. Growers need to consider managing pruning so as to avoid heavy pruning of the entire orchard in the same year. Growers may consider splitting their rambutan orchard into four, with heavy pruning carried out on a block of trees every four years. This form of management ensures that half of the orchard is in a state of growth that allows for full flowering and fruit-set to occur.

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