ORCHARD MANAGEMENT: PRUNING FOR MAXIMUM YIELD

PRUNING IS ESSENTIAL

Pruning is an essential orchard management practice and should take place for the entire life of the tree. In the early “training” years, it is aimed at manipulating growth in order to improve the framework and structure of the tree for achieving optimum yield potential. In declining years, the emphasis shifts to promoting rejuvenation and ensuring maximum sunlight to penetrate the tree canopy.

Advantages of pruning

• Improved light distribution into the canopy which is essential for flower  bud development, fruit set and growth.
• Improved pest control by allowing better spray penetration.
• Better air movement throughout the canopy, improving drying conditions  and thereby reducing the severity of diseases such as anthracnose.
• Increased fruit size because excess flower buds are removed.
• Growth of new shoots with high quality flower buds.
• Better balance between vegetative and reproductive growth.
• Higher concentrations of the hormones, cytokinin, gibberellin and auxin are found in pruned trees.
• Encouragement of regular quality crops thereby reducing the alternate bearing effect.
• Successful regrowth of diseased or damaged wood.
• Opportunity to improve the bearing structure of the tree thereby increasing production potential.
• Management of tree height.
• Encouragement of lateral branching by breaking apical dominance.

Declining productivity in unpruned trees.

As trees grow taller and denser, the lower limbs and interior limbs lose their ability to produce fruit due to increased shading.

Over time most of the fruit will be produced in the outer periphery of the tree, primarily at the top as this is the only area exposed to adequate light. Unfortunately, this is also where the most wind damage and sunburn occurs as well as poorer fruit quality, as spray penetration to those heights becomes less effective.

The cost of managing and harvesting these trees, proportionally increases with the tree height, resulting in smaller returns. It is therefore important to introduce pruning into orchards well before these unfavourable and challenging conditions are reached.

Large trees with their volume and branching complexity also make it difficult to create a simple, predictable and repeatable set of rules for pruning.

With the advent of modern, uniform, narrow canopy training with a simpler branching structure that is enforced by renewal pruning, pruning is now done to a few scientifically sound principles as opposed to “artistry”.

TYPES OF PRUNING

Regardless of basic growth habits, all trees respond similarly to a given type of pruning cut, of which there are predominately two ie. HEADING / TIPPING and THINNING.

Heading cuts or tipping

HEADING CUTS or TIPPING, remove the growing point, thereby changing the hormonal balance and forcing the tree to act accordingly. The apical dominance is removed and lateral bud break is no longer suppressed.

Thinning cuts

THINNING CUTS or THINNING is used to increase light penetration and also to remove competing or crowding shoots or limbs. Thinning cuts improve flowering.

MAKE SURE YOUR APPROACH IS CONSISTENT

In order to determine what approach to take when pruning, first ask yourself what you are trying to achieve and what you need to do to get the tree to respond accordingly.

Depending on the tree age, size and planting density your approach will vary. You also need to understand the plant physiology and development and how it responds to different types of pruning.

There are many approaches and opinions to pruning out in the industry, but whatever approach you decide to apply, ensure that you remain consistent with what you are doing and apply it to each tree so that the resultant light penetration within the tree and orchard or the regrowth is uniform.

A systematic, scientific approach to pruning with pruning “rules” enables a pruner to be easily trained and to work efficiently and without uncertainty. A selective, tree by tree, approach leads to much confusion and resultant

uniformity and consistency is lost. It must also be remembered that when pruning off a branch, the production of that branch is lost, either by pruning off the existing fruit, the flowers or the potential flowers.

The economic loss in the long run, will be the same regardless of whether you can see the fruit or not. The presence of fruit therefore, should not influence where the pruning cut should be.

POST-PRUNING MANAGEMENT

Newly exposed branches within the tree as well as the regrowth all need to be managed in order to ensure that the pruning efforts will be effective and worthwhile.

Manage sunburn

Sunburn on exposed branches and new pruning cuts as well as secondary rots and cankers can cause irreparable damage affecting tree health, performance and yield.

Protect exposed limbs

To protect the exposed limbs and pruning cuts against sunburn, a mixture of white acrylic paint, water and copper oxychloride can either be painted or sprayed on.

Sunburn on exposed branches and new pruning cuts as well as secondary rots and cankers can cause irreparable damage affecting tree health, performance and yield.

Mulch prunings

Prunings left under the tree can significantly increase the inoculum levels of fungal diseases, thereby increasing the incidence of anthracnose and post-harvest rots. However, once chipped, the mulch spread evenly under the tree from the dripline to the trunk becomes a valuable resource improving root health, soil microbiology, water holding capacity, weed suppression etc.

Manage regrowth

Management of the pruning regrowth is essential at an early stage. Thinning needs to be done in order to minimize competition for light and resources thereby enabling stronger and more productive regrowth as well as tipping to break apical dominance and encourage lateral branching for optimal production.

Pruning can be a management practice. If done correctly it can improve orchard productivity, tree performance and orchard management but if done incorrectly however can compromise production or be an ineffective and costly exercise.