There are two varieties currently grown on the Kununurra Research Facility: Kohala and Biew Kiew. These are the two most common varieties in Australia. There are also smaller plantations of Chompoo, Daw, Haew, Homestead and Ponwaii grown in Queensland.
Application of nutrients
The current fertiliser program on the Kununurra Research Facility is:
60% April, 40% August
25% February, April, August and December
50% April, 50% August
Deficiencies will be obvious in the leaves. Common deficiencies in the Kimberley are zinc, iron, boron and sometimes manganese. Micro-nutrients can be applied using foliar sprays or to the soil through the irrigation system (fertigation). Foliar applications need to be applied during vegetative flushes.
High nitrogen (N) levels will reduce flowering. However, adequate N levels are important during fruit fill.
Regular leaf and soil analysis is necessary to monitor the condition of the trees and give them what they need.
Longan's need regular irrigation. We are applying a total of 960L/tree/week at the Kununurra Research Facility, split into two irrigations per week. The tree has a shallow root system, so you don't want to push the water too far down. The regular irrigations also increase the humidity in the canopy.
There is a special trick to making longans flower. It can be the difference between no flowers and full flowering.
Apply potassium chlorate (KClO3) to the ground directly under the canopy. Avoid the sprinkler shadow to make sure that it is washed into the soil.
The Australian Pesticides and Veterinary Management Authority (APVMA) have classed KClO3 as a fertiliser with 32%K and as such it does not require a registration to be used on longan.
Kohala is a more vigorous variety, 5g/m2 will induce 85% flowering and 20% leaf drop.
It is recommended that only 2g/m2 be applied to Biew Kiew. This reduces leaf drop to 10%, but still gives 90% flowering.
Flowering occurs 6-8 weeks after application.
On the second and subsequent applications trees become less sensitive to the KClO3 and rates need to be increased to 10-20 g/m2 of the canopy applied to the ground.
Apply KClO3 in June for the best results. Stop watering the trees for three to four weeks before application (pers. comm. Peter Johnson 2017).
Other factors that also affect flowering include leaf nitrogen, the previous flowering/cropping history, level of pruning, flush development and climatic factors (temperature).
In trees with leaf nitrogen levels above 1.7% the flowering response is nearly always poor (0-25% of terminals flowering), suggesting that high leaf nitrogen can over-ride other factors influencing flowering including the rate of KClO3 application. Below 1.2% leaf nitrogen, the flowering response is nearly always good with 40-80% of the terminals flowering.
In heavily flowering crops up to 50% of panicles should be removed with a further reduction of fruit numbers if fruit set is high. Even under good management they are only capable of supporting 3-5kg of fruit/m2 of the canopy surface area.
The decline in yield with increasing thinning needs to be weighed against the improvement in fruit size, brix level, earlier maturity and market prices.
Following heavy pruning it can take two years for the vegetative growth to return to normal levels. While trees are actively regrowing following pruning the flowering response is severely reduced even with KClO3 application. This indicates that only parts of the orchard should be heavily pruned at a time so that some production can be maintained.
Foliar paclobutrazol (0.5%) applied every four months reduces the number and length of flushes following heavy pruning.
When skirting the trees trim the canopy back to just above the height of the sprinklers. This keeps the ground shaded and increases the humidity in the canopy.
Netting may be necessary if you are having problems with fruit bats or birds. Netting has been used in Queensland. See the case study on longan in the publication, 'To net or not to net'.
The canopy is very dense and there will be a thick layer of leaf litter which will suppress weed growth. The best method of weed control under the canopy is hand pulling. Longan’s are very sensitive to herbicides.
Biew Kiew fruit takes between 216 days and 286 days (7-9.5 months) to ripen depending on the date of KClO3 application, compared with 182 – 268 days (6 – 8.5 months) for Kohala.
Harvest can be predicted by using growing degree days (GDD). The GDD is calculated on a daily basis using the maximum and minimum temperature minus a base temperature:
Growing degree days = (daily maximum temperature °C + daily minimum °C)/2 - 12°C (base temperature).
This is added up until the total is reached. Kohala needs about 2900 GDD and Biew Kiew approximately 3430 GDD.