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The Open Tatura system of growing fruit has evolved from the Tatura Trellis, developed 35 years ago, and has been used commercially for about 20 years. Many types of fruit can be grown on the Tatura Trellis and Open Tatura with different configurations of tree training.

Experiments with apricot trees on Tatura Trellis began in 1976, but came to the forefront some six years ago when the variety Rival on plum or peach rootstock became popular in the Goulburn Valley in the state of Victoria, Australia. These trees produce fruit of excellent quality, color, size, and taste when grown on Open Tatura. On this system, Rival can produce a crop in the second year, and reach 23 to 27 tonnes per hectare (8.5 to 10 tons per acre) when four years old, with returns of Aus.$3 to Aus.$7 per kilogram (U.S.$1.00 to $2.50 per pound).

The following objectives aim to make the Open Tatura system more affordable for growers to plant, by reducing the capital (establishment) costs, as well as more profitable by getting the trees to consistently produce large, attractive, and tasty fruit.

Reduce capital costs

The cost of trees is often more than half the total capital cost for an Open Tatura orchard.

The method of training the trees is designed for a density of 1,960 trees per hectare (793 trees per acre). Trees are planted 1 meter (3.0 feet) apart with 5.1 meters (16.8 feet) between rows (see "Open Tatura planting").

Each row consists of two lines of trees that are separated by a 0.50-meter wide (18-inch) strip. Trees are planted diagonally left and right at a 16-degree angle from vertical. The distance between trees on one side is therefore 2.0 meters (6.0 feet). Two adjacent newly planted trees can fill this space within six months when growth starts in spring. Full canopy develops in the first year to ensure a crop in the second year, and a quick return on investment.

Build a simple and efficient tree structure

Plant two-year-old trees that were headed in the nursery. Select four shoots, preferably of equal size, that will become the leaders. The leaders are spaced 0.50 meter (18 inches) apart on the trellis to allow room for short spurs, and also allow the fruit to be adequately exposed to sunlight. The four leaders develop in the first year and form the primary structure. Spurs develop in the second year and come straight out of the leader. There are no scaffold branches or secondary structure.

Connect the four wires on each side of the trellis with strings that are 0.50 meter (18 inches) apart. Use small, plastic trellis clips to keep the strings in place and secure the leaders. This web of horizontal wires and vertical strings permanently positions the new leaders, promotes fast growth of the leaders, and prevents the growing tips from breaking off in the wind. Wind causes the tree to sway, which, in turn, alters the formation of tissues that strengthen the trunk. Since new shoots can grow about 120 millimeters (5 inches) in a week, you must frequently tape the shoots to the strings with a tapener. This is especially the case when a shoot approaches a wire and runs the risk of being decapitated when it is windy.

A rigid tree structure attached to the trellis wires also prevents mechanical damage to the fruit. Defects, such as bruises and skin blemishes, caused by branches and leaves, occur when leaders sway in the wind.

Shoots of apricot trees characteristically throw flushes of sylleptic shoots. These bunches of side shoots interfere with extension growth of the leaders, so they must be stubbed back. Other sylleptic shoots, such as single lateral shoots, must also be stubbed.

The maximum permissible height of the canopy in summer is 2.76 meters (9 feet). This is 60 percent of the actual width of the rows, which is 4.60 meters (15 feet).

Produce large, high quality fruit

Dying back or extinction of spurs is a well-known phenomenon in apricot trees. A spur is a contracted lateral. Only the tip bud of a spur is vegetative and forms leaves, and extends the spur to create new fruiting positions. But behind this short vegetative part of the spur are only flower buds. Apricots do not have mixed buds, and after flowering (or fruiting), there are no vegetative buds left to form leaves and shoots to create new fruiting positions. These spurs become extinct through excessive flowering and fruiting, and the spur quickly becomes long and bare. Large fruit of high quality are produced from short spurs that have about 15 leaves (about 310 square centimeters or 48 square inches) to support each fruit.

For the continued production of apricots of good size and high quality, fruiting units must remain young. The best way to achieve this is to renew whole leaders. The Open Tatura with four leaders has been designed specifically to renew the leaders and still maintain good production. For the first six years, each tree has four leaders. Thereafter, leaders should be renewed so that each tree has three leaders that fruit, with one leader being renewed. The sequence of leader renewal is illustrated in "Sequence of leader renewal after six years."

Spurs remain viable longer and spur extinction can be slowed when the spurs are trimmed in the fall and the flower load is reduced by thinning, followed by a quick thinning of fruit. Flower thinning can be carried out by hand or machine.

Orchardists may think that flower thinning by hand is costly, and so overlook the benefit. But hand-thinning of flowers can be very cost effective and more profitable than is fruit thinning alone. Apricot trees set more fruit than they can size. Flowers and young fruit compete for the carbohydrate and nutrient reserves that the tree accumulated during the previous season. The number of cells in the fruit flesh is determined in about the first 30 days after full bloom. This is the period of cell division. Too many flowers and/or developing fruitlets competing with other tree parts for reserves will limit cell division, and adversely affect the number of cells in the fruit and final size of fruit. Therefore, to maximize the effect on final size of fruit, the flower load is reduced by at least 60 percent at the popcorn stage before flowers have fully opened. More cells in an apricot mean that more cells can expand during the final fruit swell, and fruit is larger. Large fruit is also sweeter than small fruit. Thinning at the popcorn stage avoids damage to the emerging leaves, and allows the remaining flowers to get a bigger share of the carbohydrate and nutrient reserves when they open and get pollinated and fertilized.

Commercial trials with a new mechanical flower thinner, which is attached to the front hydraulic system of a tractor, promises to thin flowers quickly and cheaply for a modest outlay. The rotating spindle, which can be inclined to suit the angle of the canopy, has numerous plastic strings that whip blossoms from spurs. This machine is particularly efficient in thinning flowers when canopies are thin and continuous, such as on the Open Tatura.

A study of costs and returns when trees are two years old illustrates that a Rival planting on Open Tatura, producing high-quality fruit, can be highly profitable in Australia. Total establishment costs in the study were Aus.$41,000 per hectare. Operational costs for years one and two totalled Aus.$28,500 per hectare, making a total investment of $69,500 per hectare by the second year.

Estimated yields in the second year were 60 fruit (10 kilos) per tree of which 5 percent were Class 2 and 5 percent culls. Total estimated returns were Aus.$72,670 per hectare (Aus.$1.00 is equal to about U.S.$ 0.75).