HortResearch Publication - Satsuma Mandarin Production in New Zealand
Background
Satsuma mandarins have all the requirements for a successful orchard crop in New Zealand. The fruit has a well established place on export and local markets, with widespread consumer acceptance because of its easy peel, seedless nature. The trees and fruit are resistant to most diseases, and pest problems are relatively few. The compact tree habit lends itself to high density planting, and under these conditions the heavy cropping nature of satsumas results in high fruit tonnages early in the orchard life.
Chemical inputs required for satsuma production are low, both for pest control and fertilising. This lends satsumas very favourably to organic or low-chemical production. However, it should not be concluded that successful production of satsumas is a simple exercise. There are also some inherent disadvantages to this group of cultivars, such as overcropping and marginal internal quality. These can be overcome with correct management techniques, some of which require greater labour and capital input than has traditionally been the case with other citrus plantings in New Zealand.
Satsumas have been overproduced in Japan, our primary export market, during the past two decades. As is typical in glut situations, quality standards have increased so that only the best produce is saleable. Satsuma growers in Japan have employed new growing techniques to improve fruit quality, in particular internal quality. Some of these techniques are very labour intensive, and under circumstances other than the highly subsidised Japanese agricultural sectors may not be economical. However, this trend is unlikely to change, and New Zealand growers of export satsuma mandarins are thus faced with having to produce very high quality fruit.
Satsuma mandarin exports from New Zealand July 1991 - June 1995
| 1991/92 | 1992/93 | 1993/94 | 1994/95 | |
| Tonnes | 32 | 50 | 100 | 356 |
| FOB $000 | 75 | 139 | 446 | 1687 |
| $ per kg | $2.34 | $2.78 | $4.46 | $4.74
|
Satsuma exports have increased steadily over the past four seasons, as shown in the table above. The aim of this bulletin is to provide information on satsuma mandarin production so that fruit quality and export percentages can be increased.
Cultivars
The satsuma mandarin is thought to have originated in Japan 300 years ago. Since that time, many selections have been made, and continue to be made. Today in Japan, four groups of cultivars are recognised, based on their time of fruit maturity. These are: Very Early, Early, Midseason and Late. The difference in maturity time between the earliest and latest cultivars is about 3 months. The main Japanese cultivars within each of these groups are shown in the table below.
Satsuma mandarin cultivars with growing area over 1,000 hectares in Japan
| Season | Cultivar | Area in 1991 (ha) | Time of harvest |
| Very early: | Miyamoto Wase | 2,109 | Mid-September to early October |
| Ueno Wase | 2,010 | Early October to early November | |
| Yamakawa Wase | 1,175 | Late September to early October | |
| Early: | Miyagawa Wase | 14,013 | Late October to late November |
| Okitsu Wase | 11,196 | Mid-October to late November | |
| Midseason: | Nankan No. 20 | 2,268 | Early to mid-November |
| Late: | Aoshima Unshu | 6,174 | Mid-December to early January |
| Hayashi Unshu | 4,908 | Early December | |
| Sugiyama Unshu | 4,037 | Late November | |
| Nankan No. 4 | 3,116 | Early to mid-December | |
| Owari Unshu | 3,019 | Early to late December | |
| Otsu No. 4 | 2,343 | Mid-December to early January | |
| Koyama Unshu | 1,166 | Early to late December |
In New Zealand, the traditional satsuma cultivar has been Silverhill, a nucellar selection of the midseason cultivar Owari. However, during the last ten years, extensive planting of Early or wase cultivars has taken place. The main cultivars in this group have been Miyagawa, Miho and Okitsu. The only other cultivar which is grown in significant numbers is Kawano, which is later maturing than Silverhill.
The table below shows the estimated area of each cultivar at the time of a survey in 1991 (tree ages have been increased accordingly).
Estimated hectares of satsuma mandarin planted in New Zealand Tree age (years from planting)
| 4-6 | 7-9 | 10-14 | 15-19 | 20-24 | 25-34 | 35 + | Total | |
| Miyagawa | 26.9 | 42.1 | 7.2 | 1.2 | 3.0 | 0.9 | 0.1 | 81.4 |
| Miho | 7.6 | 2.0 | 0.6 | 0.1 | 0.0 | 0.0 | 0.0 | 10.3 |
| Okitsu | 10.2 | 3.2 | 1.2 | 0.4 | 0.0 | 0.0 | 0.0 | 15.0 |
| Silverhil | 4.0 | 9.2 | 14.4 | 9.8 | 6.4 | 4.6 | 1.3 | 49.7 |
| Kawano | 10.7 | 2.8 | 0.9 | 0.9 | 0.5 | 0.5 | 0.0 | 16.3 |
| Other | 1.3 | 0.5 | 2.3 | 1.7 | 0.7 | 1.0 | 0.3 | 7.8 |
| Total | 60.7 | 59.8 | 26.6 | 14.1 | 10.6 | 7.0 | 1.7 | 180.5 |
Since this survey, there have been additional satsuma plantings, possibly to the extent of 40-50 hectares. Satsuma cultivars have been the most extensively propagated in New Zealand citrus nurseries in the past two seasons - the graph below shows the numbers of high health satsuma buds supplied to nurserymen by the NZ Citrus Budwood Scheme during 1994 and 1995.
Satsuma mandarin buds supplied by the NZ Citrus Budwood Scheme 1994 & 1995
In the past 8 years, several satsuma cultivars have been imported by the Citrus Sector and HortResearch. These are planted in a cultivar trial which has yet to crop, but budwood will be made available to propagators as soon as the first fruit can be confirmed to be true to type. HortResearch is also planning to import some of the Very Early or goko wase Japanese cultivars, none of which is currently available in New Zealand. The table below summarises the present cultivar situation.
Satsuma mandarin cultivars available from NZ Citrus Budwood Scheme
| Recommended | Other options | Experimental | |
| Very Early | -- | -- | To be imported 1996/97 |
| Early | Miho | Okitsu, Miyagawa | Okitsu reselection*, Valles* |
| Midseason | Silverhill | -- | Kuno*, Seto*, Dobashi Beni* |
| Late | Kawano | Ishikawa | Aoshima |
Rootstocks
A citrus rootstock can provide: improved sugar:acid ratios, larger fruit size, earlier or later fruit maturity, increased or decreased tree vigour, improved yield efficiency and longer fruit storage life.
The New Zealand citrus industry is almost entirely dependent on one rootstock, trifoliate orange (Poncirus trifoliata), known locally as 'trifoliata', or simply 'tri'. Although trees on trifoliata produce high quality fruit and have tolerance to many soil diseases and pests, this stock also has some shortcomings: small fruit size, high fruit acidity, and incomplete compatibility with some scion cultivars.
Many new rootstocks have been developed in the past few decades, in particular trifoliata hybrids (citranges, citrumelos). These have potential to improve yields and fruit quality in New Zealand orchards, but like imported scion cultivars, they must first be thoroughly tested under local conditions.
Until such time as a new rootstock is thoroughly proven, trifoliata remains the recommended rootstocks for satsuma mandarins. Although careful comparison of the many strains of trifoliata has not been done in New Zealand, the Californian selection 'Rubidoux' and the Australian selection 'Accession 22' are suggested.
Propagators have experimented with small batches of trees on Troyer or Carrizo citrange and, to a lesser extent, Flying Dragon dwarf trifoliata. In overseas trials, Morton and Rusk citranges have both increased Brix levels in satsuma fruit. All these stocks are worth planting on an experimental basis. Silverhill trees growing on Troyer citrange in Kerikeri have produced larger canopies, higher yields, and earlier fruit maturity than trees on trifoliata of the same age and in the same orchard block.
By the Year 2000, a rootstock trial at Kerikeri Research Centre will have identified whether any of the 10 stocks under test are capable of producing better internal quality of satsumas than trifoliata.
Miyagawa satsuma mandarin rootstock trial, Kerikeri Research Centre
| Rich 16-6 trifoliata | Benton citrange |
| Rangpur X Troyer | Rusk citrange |
| Swingle citrumelo | Savage citrange |
| Carrizo citrange | Troyer citrange |
| C-35 citrange | Cleopatra mandarin |
Planting
Tree spacing:
Satsuma on trifoliata rootstock make small, naturally dwarfed trees. The intense flowering and cropping on young trees contributes to keeping them small. Compared to other citrus cultivars, satsumas are ideally suited for high density planting. This is particularly so for the Early cultivars; Silverhill is somewhat more vigorous, and Kawano noticeably so.
The highest density plantings of Early cultivars have been at Kerikeri, where a triple row system has been used, giving 3,750 trees per canopy hectare. This is in effect a 2 X 1 metre pattern, with every fourth row open to allow machinery access. The initial crop yields from these blocks have been very high, reaching 40 tonnes per canopy hectare by Year 6. However, tree crowding has occurred 6-7 years after planting, and removal of complete rows and trees within the rows has been necessary. The resulting spacing is either 4 X 1 metres or 4 X 2 metres, giving 2,500 or 1,250 trees per canopy hectare. These different configurations are depicted below.
An alternative starting option for Early cultivars is to plant trees in rows 4 metres apart, and at 1 metre within row spacing. Single rows will be necessary if row mounding is to be done, as discussed later. Transplanting of 6-8 year old trees is feasible, and machinery for this purpose has been developed by a Kerikeri orchardist. Initial transplantings appear highly successful, but of course additional land must be available for the expanded plantings.
Tree spacing configurations for satsuma mandarins
2 2 4 2 2 4 2 2 * * * * * * * * * 1 A * * * * * * * * * 1 * * * * * * * * * 1 3,750 * * * * * * * * * 1 trees/ha * * * * * * * * * 1 4 4 4 4 4 * * * * * * 1 B * * * * * * 1 * * * * * * 1 2,500 * * * * * * 1 trees/ha * * * * * * 1 4 4 4 4 4 * * * * * * C 2 * * * * * * 1,250 2 trees/ha * * * * * *
• either A or B pattern recommended for Early cultivars, with tree removal at Year 7-8 to reach C pattern
• Silverhill should be planted to B pattern, with later tree removal to C pattern
• Kawano should be planted to C pattern
Mounding:
Hanging fruit on the trees in late autumn to allow acidity reduction carries the risk of rinds becoming excessively puffy. 'Floating skin' is not acceptable on the Japanese market, and also makes the fruit very sensitive to wastage during picking and packing.
Control of soil moisture in late summer and autumn is essential for prevention of puffing. Most satsuma orchards in Japan are on steep terraced hillsides which provide excellent natural drainage, but where orchards are situated on flatter terrain, mounding has become a common practice. Mounds are steep walled and 500 - 750 mm high, with surface drainage afforded by the central ditches.
All new plantings in New Zealand should be on mounded soil to raise the root zone above the water table. New orchard blocks should be situated on gently sloping ground, and mounded rows should be oriented to allow rapid outflow of rainwater. Older plantings on flat land should be modified to allow better drainage and egress of rain water. This can be achieved by digging central ditches between existing tree rows, in effect leaving the trees standing on mounds.
Fertilising
Satsuma trees are not vigorous, and despite the heavy crops carried, requirements for the major elements is relatively low. This lends satsumas to low fertiliser input systems, such as organics or biodynamics.
Pre-plant fertilising is important to correct soil pH, and to add the poorly soluble elements calcium, phosphate and magnesium. Amounts to broadcast should be determined by soil analysis. Pre-plant addition of potassium is not recommended for satsumas.
Young trees need small, regular amounts of nitrogen. These can be applied via solid dressings, fertigation, foliar sprays or a combination of these methods. Trace elements should be regularly applied by foliar spraying - at least 3 sprays per season.
After the first two seasons, during which crop is removed from the trees to allow canopy growth, fertilising should be based on leaf analysis. Leaves are sampled in February/March each season, from non-fruiting shoots from the previous spring.
Typically, light nitrogen applications will be needed annually, and for improved fruit quality, these should be applied in late autumn to allow tree reserves to build up for the coming spring flush. Potassium is very rarely needed, and mixed fertilisers should be avoided for this reason. Nitrogen can be applied as urea or calcium ammonium nitrate, or if calcium is also deficient, as calcium nitrate. Foliar applied urea (1%, low biuret) is an effective way of providing light nitrogen quantities. Typically, a cropping satsuma planting will require about 100 kg of elemental nitrogen per annum, and certainly never more than 150 kg. However, amounts must always be determined by leaf analysis.
Phosphate is often required, especially if insufficient amounts were supplied pre-planting. The correct balance of phosphate to potassium is required for modulating citric acid levels in the fruit - high potassium and low phosphate levels will result in very acidic fruit. This situation is common where mixed fertiliser have been used in the past.
Magnesium is required in significant quantities by satsumas - this can be applied as soluble magnesium sulphate in the irrigation system, or as a foliar spray, or as a solid (Kieserite). Slower release forms are calcined magnesite (Calmag, Magnox) or dolomitic lime.
Calcium deficiencies are often also detected by leaf analysis. Liming is the best long term means of adding calcium, but if the soil pH is already above 6.0, then gypsum should be used. Foliar calcium sprays are also available - calcium nitrate (2%) sprays are commonly applied overseas to oranges at colour break to improve rind strength and fruit storability.
Regular foliar sprays of the trace elements zinc and manganese are needed every season, and molybdenum can also be deficient. Copper is also an essential element which is generally well supplied by disease control sprays, but should not be ignored on young, non-cropping trees.
Fruit thinning
Of all the orchard operations required on a satsuma block, fruit thinning is the most vital. The satsuma tree has almost no ability to regulate its crop from season to season, and without intervention will quickly develop a severe alternate bearing habit - vast numbers of small fruit in the on year, followed by an off year with almost no crop.
Newly planted trees should not be allowed to crop for the first two seasons. Even one or two fruit left on a young tree will severely retard its growth. Winter applications of gibberellic acid (GA) will reduce flowering - a rate of 50 ppm is recommended in June. Addition of the surfactant Pulse will increase the effectiveness of GA.
Cropping trees need to be hand thinned after natural fruitlet drop (December/January). Experiments have shown that each fruit on an Early cultivar satsuma tree needs about 20-25 leaves to achieve export size, and allow the tree enough reserves to crop in the following season. For Silverhill trees, the ratio is about 15-20 leaves per fruit. Some initial careful leaf and fruitlet counting is needed to see what these crop loads look like, but thereafter thinning needs to be done quickly by eye, with some follow up quality control. Very often, a tidy up thinning is needed in February to remove missed fruitlets.
GA also assists fruit thinning by reducing the number of fruitlets which need removing. A 25 ppm, full cover spray in June is recommended.
With increasing emphasis on internal quality for export fruit, it is important to adjust fruit thinning to leave fruit in the best sites on the tree. In Japan, positioning of fruit around the canopy is of prime importance - fruit which grow on vigorous upright shoots will have thick stalks and will have poor quality. Fruit hanging on thin, drooping shoots around the sides and skirts of the canopy will produce the highest quality fruit, whereas internal, shaded fruit will have lower Brix levels.
Pruning
Pruning should be carried out in August-September. The aim of pruning is to prevent shading of branches, and to accentuate those shoots which will carry high quality fruit. Horizontal growth is left - these produce fruit that hang down on thin stalks, and have the highest quality. On young trees, vigorous summer shoots are cut off. Pruning also helps alleviate alternate bearing.
Disease control
Satsumas have been selected over the centuries in Japan for their tolerance to wet weather diseases. The fruit rinds are resistant to Alternaria and Botrytis, and only very slightly susceptible to citrus scab (verrucosis). Melanose is the main rind blemishing disease, but is only a problem during excessively wet springs and early summers. Copper or mancozeb sprays at petal fall in November are recommended, repeated 2-3 times at three week intervals until mid-January, depending on rainfall. As a rough guide, a protectant fungicide needs to be reapplied after each 100 mm cumulated rainfall. Annual removal of all dead wood and twigs from the centre of tree canopies will dramatically reduce melanose infection.
Young satsuma shoots can be killed by Sclerotinia, which infects the tissue during windy, wet periods. If this is a problem which reoccurs in an orchard from season to season, then a spring application of benomyl (50 grams/100 litres) is recommended. Sclerotinia damage is not worth treating if it only occurs sporadically, but young trees in exposed blocks should be sprayed because large amounts of the canopy can be infected.
Three weeks prior to harvest, a skirt spray of copper or mancozeb onto the lowest metre of canopy will prevent infection by brown rot (Phytophthora) spores, which are splashed up from the soil onto the fruit by raindrops.
Pest control
Thrips Stem-end blemish is probably the most serious pest cull factor for export satsumas. Damage is caused by thrips feeding shortly after petal fall, and results in the typical silver-grey ring around the calyx. Thrips are effectively controlled by organophosphate sprays such as diazinon, but a search is underway for 'softer' options. Abamectin and natural pyrethrum look promising, but are yet to be fully evaluated and registered.
Fullers rose weevil is an important quarantine barrier pest for fruit exported to Japan. Although adult weevil damage by leaf feeding is usually minimal, the laying of egg rafts under the fruit calyx is a serious problem. Consignments of fruit landing in Japan are stringently inspected for pests, and in the past season many were fumigated because of FRW egg presence. The only feasible control method at present is to use trunk barriers, in combination with tree skirting and good weed control, to prevent access of the flightless adult weevils into the tree. Trunk barriers must be applied early in the season (October) before adult emergence from the soil begins.
Satsuma trees are very susceptible to lemon tree borer, and removal of borer infested branches is a laborious but essential annual chore for orchardists. Infested branches should be burned or mulched, because the larvae can successfully live in dead wood. Infestation can be reduced by restricting pruning to the winter months when adult borer flight is minimal. Any large pruning cuts should always be dressed with a pruning paste (not grease), preferably with a synthetic pyrethroid added.
Several scale species infest satsumas. The most common are soft wax scale, Chinese wax scale, and black (= olive) scale. Less common but sometimes problematic are greedy scale, soft brown scale and cottony cushion scale. The main visible symptom of scale on fruit is sooty mould, which can be difficult to remove in the packhouse. It is rare to find scale on fruit at harvest, except for greedy scale - this species has caused problems for satsuma exporters in the past 2 seasons, and because of the small size of the scales, needs to be carefully inspected for. Because all scales go through a vulnerable crawler stage, they can be effectively controlled by monitoring and application of carefully timed oil sprays. A recently registered alternative to oil for scale control is the insect growth regulator buprofezin (Applaud). This chemical interferes with the moulting of sucking insects, but is safe on predators and parasites.
Citrus red mite damage is mainly to leaves, where the sucking of chlorophyll results in a typical bronzed appearance. Young fruit can also be damaged during severe mite infestations. Mite outbreaks are often the result of broad spectrum sprays which kill the natural mite predators. Several miticides are registered for use on citrus, and oil sprays are also effective.
Caution on oil use While oil sprays are good 'soft option' controls for scales, they must be used with caution on citrus cultivars which have marginal internal quality such as satsumas. Excessive oil sprays have been shown to decrease Brix levels in fruit, and delay fruit colouring. The greatest risk time for application is during the second half of fruit development i.e. from January onwards. As a guide, it is suggested that oil should not be applied after January, and that the total oil used in the season should not exceed 2% (e.g. two 1% sprays, or four 0.5% sprays).
Katydids are the suspected cause of deep, silver-grey scarring which occurs on the exposed surfaces of satsuma fruit. This damage is only sporadic, but can be serious in some seasons and in specific orchards. In Australia, young stages of katydid cause considerable damage on young citrus fruitlets very early in the season, and these feeding marks develop into deep scars as the fruit grow. There are no registered remedies in New Zealand, but in Australia maldison is sprayed when damaged fruitlet levels reach more than 5%.
Aphids usually do not warrant controlling, except on young trees, where significant damage to foliage can occur. Pirimicarb (Pirimor) has proven a very selective aphid controlling spray, with no harmful effect on predator insect and mite species. It is not currently registered for use on citrus in New Zealand, although it is extensively used in Australia.
Harvesting
Internal quality
The external rind colour of satsumas is not a good indicator of the internal quality of the fruit. The Early cultivars tend to colour fully before reaching acceptable eating quality, as measured by the sugar to acid ratio of the juice. Conversely, fruit on old Silverhill trees can reach acceptable internal quality before all the green colour has disappeared from the rind. Juicing a sample of fruit and checking the sugar (Brix) and acid (% citric acid) levels is the only accurate way of determining whether the crop is ready for harvesting.
Different internal quality standards are used for the local and export markets. For the local market, a Brix:acid ratio of 7:1 is the recommended minimum, and this should be reached on a sample of 20 fruit typical of the colour which is to be picked.
For the Japanese export market, much higher internal quality is required. Brix needs to be at a minimum of 10, and preferably at 11. These figures refer to minimums above which the majority of fruit should be. When testing samples of fruit, the variability of individual fruit should be noted. For most New Zealand orchards, variability is high - this means that for 80% plus of individual fruit to be above 10 Brix, the average of a 20 fruit sample will probably have to be 11 Brix. These values need to be calculated for each exporting orchard each season. Although many individual fruit will reach 10 Brix, a further challenge is to determine where these fruit occur on the tree canopy, and aim through pruning and thinning to promote and select these sites. In Japan, trees are not expected to begin producing high quality fruit until they are 8 years old.
Acidity at point of sale in Japan should be 0.8%. This means that fruit should not be harvested before acid levels drop to 1.2%, and should be cured prior to shipping to drop acidity to 1.0%.
Handling
Satsuma rinds are very sensitive to rough handling during harvest. Wherever possible, fruit should not be picked while still wet from rain or dew. Dry fruit has lower rind turgor, and there is less risk of oleocellosis occurring. The fruit needs to be clipped flush at the button, but great care must be taken not to cut the rind during clipping. It is often better to use two actions - stalk clipping, and then trimming at the button.
Picking bags or containers need to be free of grit and stalks, and fruit bins should be smooth walled. Rubber bin liners prevent fruit from bruising. Careful transport to the packhouse is important - trailers bouncing over rough roads can severely damage the fruit.
Storing fruit pre-packing
In Japan, early season (wase) satsumas are stored by the grower for 5 days before taking the fruit to the packhouse. For midseason cultivars, fruit is stored for up to 3 weeks before packing. This period is required for citric acid levels in the fruit to decline to acceptable levels. Acidity will reduce by 0.2-0.3 % by storing under low humidity (80%). Fruit is typically delivered to the packhouse at 0.8 % acidity. This may become standard practice in New Zealand, with fruit either being cured on the grower's property or at the packhouse.
Source:
HortResearch Satsuma and Manderin Workshop conducted November, 1995.
Made available for HortNET, May 1996.