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Trellis drying sultanas | AG0588 |
David Braybrook, Mildura
July, 1997 |  |
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Introduction
Trellis drying is a well proven system of producing quality dried fruit. Many benefits result from trellis drying sultanas, such as reduced labour requirements and less risk of crop loss in a wet year. The cost saving benefits are essential for the future viability of many vineyards. The development of new technology and management systems are making trellis drying easier and more efficient. Trellis drying must be considered as a complete harvest system, requiring new management skills and changed vineyard practices. Paying attention to detail in each activity is essential for a successful operation.
Trellis drying requirements
To determine whether trellis drying is an option for you, the suitability of existing vines and the vineyard set-up requires assessment.
Vine vigour
Summer pruning has the potential to reduce vegetative growth and yields. Therefore, vines lacking vigour (producing on average less than 5.6 tonnes per hectare) are generally unsuitable. Where vines are grafted to vigorous rootstocks, summer pruning can be an effective way to manage excessive vigour, and in some cases can lead to increased yields.
Trellis
A range of trellises are used for trellis drying. It is important that the trellis design matches vine vigour and enables easy wetting and harvesting of bunches. The minimum requirement is for a narrow-T with one vertical foliage wire. This may lead to problems with fruit clumping and poor spray coverage. Single wire and narrow-T are not suitable for maintaining vine productivity or consistent production of high quality dried fruit. Wide-T trellises are suited to trellis drying and enable the yield potential of vines on vigorous rootstocks to be realised. However, a suitable harvester must be used to prevent significant damage to trellis and vines. Taller trellis systems such as the Shaw swingarm trellis have been developed specifically to optimise the benefits of trellis drying, enabling almost complete mechanisation. Refer to Agriculture Note AG0586: The Shaw swingarm trellis.
Vineyard set-up
It is important that the vineyard set-up will not impede the movement of wetting and harvesting equipment. Minimum requirements are a row width of 3m (10') and headland turning space of 4.9 - 6.1m (16' - 20'). Other potential obstacles (trees, drainage pits, etc.) must also be considered.
Pre-season preparation
Vineyard floor management
To successfully trellis dry, it is essential to maintain optimal vine health and productivity.
Soils
Having "good" soil structure is essential for adequate aeration and drainage, which enable optimal root growth and function, and improve irrigation efficiency. Soil structure is commonly improved through covercropping programs or the addition of mulch . Regular monitoring of soil and vine nutrient levels will ensure that the most appropriate fertilisers are applied.
Irrigation
Vines should be irrigated as soon as practicable before cutting, and after harvesting. The need for the vineyard to be accessible to machinery for wetting and drying activities will influence the irrigation strategy. Overhead irrigations should be avoided while fruit is drying on the vine.
Weeds
Effective undervine weed control is always important, as weeds compete with vines for water and nutrients. Preharvest control is essential, as taller weeds such as fat hen (Chenopodium album L.) and gentle Annie (Cenchrus incertus Curtis) can cause problems with harvesting, and may contaminate the final product.
Winter
Pruning
Paying attention to cutting-out and rolling-on has an important influence on the ease and efficiency of other operations. In winter, the desired number of fruiting canes are rolled onto the wire as near as possible to the crown of the vine. A sufficient number of spurs should be left near the crown to produce well positioned replacement canes for the next season. Canes should not be allowed to cross over the crown. This will assist in the identification of fruiting canes for summer pruning.
Spring
Crown bunch removal
Crown bunches are those growing too close to the vine crown or cordon to be cut for trellis drying. Their removal is important, as they can represent 10 to 20 percent of bunches. These fresh bunches can contaminate harvested fruit, causing problems of adhering leaf and undesirable colour variations. The removal of unwanted bunches can occur in spring. The best time is before the canopy falls, when these bunches are easier to locate. With spring removal, there is little effect on yield due to the increased growth of remaining bunches. Correct winter pruning will help to reduce the number of crown bunches.
Summer
Cane cutting
Trellis drying requires vines to be summer pruned. This involves cutting all fruit bearing canes, while leaving at least 50 percent of the foliage. Excessive canopy removal can cause reductions in future yields, and missing fruiting canes can result in fresh fruit contaminating the harvested product. Cane cutting usually occurs in the last two weeks of February, and should be completed by the 7th of March. Cutting can be conducted earlier if rainfall threatens to damage the crop. Ideally, cutting should not begin until the fruit is mature (200 Brix/110 Baume). It has been shown that immature fruit is more difficult to wet with the drying emulsion. It is essential to check for any uncut canes a few days after cutting, which should be the time when crown bunches are picked. A skilled summer pruner can hand-cut about 0.4 hectares per day. The Shaw swingarm trellis enables mechanised cutting, with about 0.4 hectares cut per hour.
Crown bunch removal
Many growers remove crown bunches during the harvest period. If removal has occurred in spring, some checking and further picking is usually required at harvest time. Bunches are hand-picked about three to five days after cane cutting, when they are easier to distinguish from those on the cut canes. These bunches can be placed onto the fruiting wires to ensure collection by the harvester, or they may be rack dried.
Wetting bunches
Achieving good coverage of bunches with the drying emulsion is essential for the production of high quality trellis dried fruit. If fruit is not properly wet, fruit quality will be low, regardless of how well all other operations are performed. The drying emulsion should be applied within a day of cane cutting. Recent research has shown that a mix of 0.6 percent potash and 0.5 percent oil is sufficient to dry fruit. A second application may be required if rain removes the emulsion within three days of application, or if inadequate coverage has occurred.
Wetting Equipment
Because wetting is such a critical task, it is important that the most efficient equipment is used. Purpose built wetting machines are the most effective, having been designed specifically for trellis drying. It is important that equipment is set-up to enable thorough wetting of bunches. The number, location and direction of nozzles will vary according to the trellis type. When setting up, do small runs and constantly go back and check bunches to ensure thorough coverage into the centre of the biggest bunches. The volume of spray applied is generally high and is influenced by the crop load and ability to penetrate fruit through the canopy. Generally 22,000 to 33,000 L/ha is applied, with about 7,000 to 11,000 L/ha left on the vines. Losses are significantly reduced by catching and recirculating the run-off. The ground speed is determined by the crop level and the efficiency of the wetting equipment. A speed of around 1 km/hr, enables growers to wet between 0.2 and 0.4 ha/hr. A loan scheme provides access to a wetting machine for first time trellis driers with a small area. Detailed plans are also available for growers who wish to construct their own. For further information contact Agriculture Victoria, Mildura (Telephone: 03 5051 4500). Contractors are also an option.
Harvesting
Harvesting occurs when the moisture content of berries falls to about 16 percent. This is generally 10 to 20 days after cutting. Harvesting usually takes place in the afternoon and evening when fruit will be drier and stems more brittle. The aim of harvesting is to remove the maximum amount of fruit, while causing minimal loss of leaves and damage to replacement canes for next season's crop. Harvester preparation is therefore important. The beater needs to be set at the speed required just to remove the fruit. The amount of fruit falling in front of the collection system needs to monitored, and the beater action should be adjusted accordingly. The harvester's cleaning fans remove dried leaves and other trash, and must also be monitored to prevent significant berry wastage. Fruit that is not removed by the harvester may be collected by hand.
Harvesting Equipment
A number of types of harvesters are used to remove trellis dried fruit. The high purchase costs of new harvesters may make forming a syndicate a viable option, or it may be possible to buy a second-hand machine.
Contractors are also an option, with:
- Self propelled upright harvesters costing around $265 - 300/hr and picking between 0.6 - 0.8 ha/hr (1.5 - 2 acre/hr).
- Shaw machines costing around $120- 150/hr and picking 0.3 - 0.4 ha/hr (0.75 - 1 acre/hr).
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Modifications may be required to enable harvesters to pass over the taller Shaw swingarm trellis, and a specialised harvester is currently being developed for this system.
Finish drying
Trellis dried fruit is rarely harvested below 13 percent moisture. Therefore, most trellis dried fruit needs finish drying. This should occur as soon as possible after harvest, as fruit can darken during storage. As harvesters can remove large amounts of fruit in a short time, the finish drying process can not handle all of the fruit at once.
Therefore, finish drying can often be the "bottleneck" or limiting factor in trellis drying. Ground sheets may be used, but is more labour intensive and increases the risk of rain damage and contamination from weed seeds and ground debris. Bin drying systems tend to be the preferred option, with equipment ranging from the Hudson Bin Driers to hot air circulation systems. Portable bin systems are the best as they can be mechanically emptied. It is essential to cool the fruit before boxing, by running the dehydrator fan for a few hours. This reduces the level of fruit clumping and enables the colour to be retained.
Economics of trellis drying
Increases in production costs and downward pressure on prices due to international competition, continues to erode the profitability of dried vine fruit production. Growers must therefore reduce costs to remain viable in the industry. Trellis drying provides the opportunity to do this, through the significant labour reductions that result from mechanisation. Costs of harvesting using trellis drying are relatively fixed per hectare. Therefore, the heavier the crop, the lower the cost per tonne. Yield increases may result from harvesting later, at a time when the drying ratio has improved. Risk management is also enhanced, as rapid crop cutting enables the crop to be salvaged in a wet year.
Future of trellis drying
The development of new trellis systems and equipment will continue to improve the efficiency of trellis drying. Trellis drying provides opportunities for increased mechanisation of dried vine fruit production, and therefore, has a key role to play in the future of many vineyards.
Further information
Agriculture Note AG0586: The Shaw swingarm trellis.
AgVic (1996) Trellis Drying Sultanas: Drying For Profit. Agriculture Victoria (24 pages)
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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