By Kevin Lacey

Agriculture WA.

When it comes to citrus, pruning is fundamental to the future of your enterprise.

Citrus trees are pruned in order to:

· keep trees a manageable size and within allocated space

· increase ease of access to trees allowing for easier harvest and management

· allow light penetration into the canopy

· prevent crowding of main scaffold branches and to remove crossing branches

· remove or shorten water shoots to prevent them from becoming dominant

· allow air circulation and access under trees (skirt pruning)

· increase blossom quality

· increase fruit size and yield

· prevent fruit damage due to limb rubbing.

Avoid overpruning. The leaves are the manufacturing part of the plant – removing too much of the canopy will reduce tree growth and crops. Citrus bark also burns easily if over-exposed to the sun.

Pruning should involve removing unhealthy, unwanted and poorly positioned branches but minimise the loss of healthy foliage. The best time to prune is soon after harvest in winter to early spring before bud break. For late varieties where two crops may hang on the tree at once some of the new crop may be lost.

The benefits of pruning can be reduced or delayed if trees are not pruned at the right time and in the correct way.

Creating a good frame

There are five pruning strategies within the canopy aimed at different stages in the life of the orchard. This pruning is done by hand.

· Initial heading at planting will balance top growth in relation to the root system. Branching should not be allowed on young trees until they reach a height of 50 to 60cm. Young trees should have 20cm of straight trunk above the bud union before branching. Heading at this height will reduce the amount of time spent on skirting in later years.

· Main scaffold branches should be staggered as too many branches initiated in one spot can cause crowding and weakening in later years. Aim to maintain about eight main scaffold branches as dominant limbs, once established. Prune subsidiary shoots from the main scaffold branches to reduce competition. Select the more horizontal shoots as fruiting wood.

· Thinning out of branches as trees age allows light to penetrate into the centre of the tree. This helps to maintain fruit production inside the canopy, as well as on the periphery.

· Chunk pruning on older trees allows light into the center of the tree. In hedgerow plantings, remove a whole scaffold limb on opposite sides of alternate trees. This allows access for pickers into the inside of the tree. The extra light also improves the colour of internal fruit. Some growers remove a large scaffold branch from a different section of the tree every two to three years. Where trees are more widely spaced, a large scaffold branch on the north side of every tree is removed to improve access and to increase light penetration.

· Skeleton pruning is normally a last resort with old trees to get a few more years from them. Prune in autumn and cut back all shoots, leaving only the main scaffold branches. The scaffold branches should be painted with watered-down white acrylic paint to protect the bark from sunburn until the tree refurbishes itself.

Skirting (skirt pruning)

Skirting is the removal of branches and limbs which hang down to the ground. It should be done as soon after harvest as possible.

Skirting of Valencias and summer navels is more difficult as the trees are carrying two crops. Some crop loss is inevitable whenever late varieties are skirted. Skirting in October or November after fruit set is probably the best option.

Mature trees should be skirted to a height of at least 75cm. This allows for branches dropping lower when fruit develops. Machine skirting is quick and easy.

Skirting provides the following advantages:

· Better air movement under the trees

· Easy application of below-tree herbicides and fertilisers

· Reduced access into the tree for insects and pests such as fuller’s rose weevil and snails

· Clear throw of irrigation water from mini-sprinklers and ease of checking on the operation of mini-sprinklers and drippers

· No splashing of soil-borne fungi into the canopy from rain or irrigation

· Better access when harvesting

· Prevents lower set fruit from hanging in the dirt

· Required practice as part of the market access protocol for some export markets.

Hedging and topping

With increased plant density and hedgerow plantings, machine pruning becomes more necessary to save time. This is usually when trees are too high to harvest easily and grow too wide into the row to access.

There will always be some crop loss from hedging. The benefits of improved access and increased fruit size have to be weighed against the crop loss and the cost of the operation. Hedge and top only as much as necessary.

Benefits include:

· Restored inter-row access (hedging)

· Reduced tree height (topping)

· Trees can be re-invigorated

· Fast operation – can be done quickly.

Side hedging can be done at an angle of 15° to 25° from the vertical to allow better light penetration to the lower parts of the canopy. Trees can be hedged at 25° to form a triangle shape and then flat-topped.

If side-hedging at 15° from the vertical, trees also need to be topped from both sides at 30° from the horizontal to allow light penetration to lower parts of the canopy.

Machine pruning can be carried out over a three-year period. Prune one side in one year, the other side the following year, and the top the year after. This reduces crop losses in any single year.

Alternatively, hedging of entire trees can be carried out in one year, on every second row. Some growers carry out side hedging and topping on the entire block in the on-crop year and skirt pruning in the off-crop year. It is important to begin machine pruning in good time, otherwise, the cuts will be too large and crop losses too high.

Regrowth management

Regrowth management resulting from pruning is vital if the full benefits are to be achieved. It is ideal to do this several months after pruning in late summer to mid-autumn, when regrowth is about 30cm long.

Healthy trees will produce localised shoot growth around the site of large cuts after pruning, as well as general regrowth through the canopy as a result of increased light intensity.

Watershoots coming from low down on the trunk or main scaffold limbs should, in most cases, be removed entirely. Other excess shoots can be thinned by hand, and spaced to about a hand span apart. Both topping and hedging force regrowth shoots to branch.

Equipment

Hand, battery or air-operated secateurs are ideal for pruning out smaller branches on citrus.

Air or hydraulic secateurs on extension poles are also available for pruning large trees and to reduce ladder work. Conventional chainsaws can be used to remove large limbs. Machine-operated hedging equipment should only be used by an appropriately trained operator.

Precautions

· use only properly sterilised saws and secateurs. A freshly mixed spray or dip of one part chlorine bleach plus two parts of clean water can be used.

· oil instruments after use to prevent rusting and corrosion.

· avoid contamination of cuts with soil.

· protect regrowth from foliar pests and pathogens.

· do not open trees excessively in any one season as sunburn can severely damage the bark. If there is a risk of sunburn apply white acrylic paint to exposed trunks and limbs.

· ensure that anyone operating mechanical saws and machinery fully complies with occupational health and safety training requirements. (Mechanical saws and pruning equipment can be very dangerous if misused.)

Acknowledgements

This page replaces Farmnote 60/95 on Pruning citrus trees by John Dick. Some information was also provided from Dr Andrew Krajewski, International Citrus Technologies.