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202012 Fresh Quarterly Issue 11 03 A Handle On New Trees
Issue ElevenDecember 2020

Get a handle on new trees

It’s not just up to the nurseryman. By Grethe Bestbier.

Much can go wrong between the lifting of nursery trees and their establishment in the orchard. Fresh Quarterly spoke to three horticulturists for tips on how careful handling of trees can prevent later problems.

Why all the problems?

“You can really ruin a tree during its handling,” says Prof. Wiehann Steyn, assistant general manager at Hortgro Science. “Even if you receive the most beautiful tree, it can suffer or die in your orchard because of mistakes that the producer makes, without the nursery being to blame.”

Various factors can contribute to tree mishandling. A lack of communication between the nursery and producer can be problematic.

“If the nursery does not communicate with the producer about when the trees are lifted and when they should be fetched or delivered, many mistakes can potentially creep in,” says Prof. Karen Theron, Hortgro Chair in Applied Preharvest Deciduous Fruit Research in the Department of Horticultural Science at Stellenbosch University.

The devil is in the details, as Marno van der Westhuizen, research implementation manager at Hortgro Science, explains. “I think producers may sometimes miss small but critical steps. The small things can be the difference between an orchard shooting the lights out or not performing up to expectations.”

Rooting for a good start

Most deciduous fruit trees are lifted in the nursery and then transported and handled as bare-rooted plants. Root loss during lifting and handling contribute to transplant shock. Disturbing the root system as little as possible is a golden rule of good nursery-tree handling. It is important to keep as much as possible of the tree’s roots alive before and after planting.

White roots are a welcome sign of new life, but these roots should only start growing once the trees are planted, and not a moment sooner. When white roots sprout too soon, for example while trees are in cold storage, they are damaged very easily. White roots may even form when trees are heeled in on the farm after delivery. If trees spend too long in trenches prior to planting, the white roots that sprout are likely to be broken off when the trees are again lifted.

The problems associated with early growth of white roots can be reduced by good timing, and potentially avoided altogether by using containerised trees and autumn planting.

When trees chill

It has become common practice to put especially apple trees in cold stores before planting to accumulate enough chill to ensure good bud break and improve future orchard performance.

“In most South African regions, we typically have too little cold,” explains Steyn. “Cold storage not only provides a potential storage space for trees if the orchard is not ready yet for the trees to be planted, but also breaks endodormancy.”

To ensure good bud break trees have to undergo effective chilling, which refers to the range of temperatures which breaks the tree’s endodormancy.

“Effective chilling is a physiologically active process, meaning that some actions have to be triggered. If it is too hot or too cold, nothing will happen,” clarifies Theron.

It is preferable to keep trees at the lower end of the temperature range where positive units accumulate (2ᵒC–4ᵒC). If producers store the trees with fruit at too low a temperature (below 1.5ᵒC, according to the Richardson model), no effective chilling accumulates. The tip of the trees might also not be properly hardened off and can be damaged at low temperatures.

Deciduous trees are fairly resilient in their hardened-off, dormant state, but their roots and other organs can be damaged by either too little or too much water.

“A high humidity in cold stores is important to avoid the drying of above-ground parts. Many producers keep their cold stores at humidity levels as high as 90%,” says Theron.

Planting for success

Many simple mistakes are made during the planting of trees. According to Steyn, preparation is critical.

“Everything has to be ready, including yourself and your team. It does not help if you start planting trees while the irrigation is not ready, and you only start irrigating your trees a week later. In this case, you are working with bare-rooted trees, so you have to wash in the soil around the roots. It is of no use to have air pockets surrounding roots beneath the ground.

“Another thing that could happen is preparing to plant on a certain date, but having another operator or role-player delayed or cancelled. Now, all of a sudden, trees have to remain in cold storage or in trenches for longer than you planned.”

Bare-rooted trees are at risk of drying out during transport, storage, and planting. Drying damages the root system and contributes to deaths of young trees after planting.

Theron adds that other simple things like incorrectly preparing the planting holes can also be detrimental. “What often happens is that planting holes aren’t made big enough, forcing you to cut off roots for the tree to fit into its hole.

“It is all good and well to accept that the nurserymen did their jobs well and you are receiving a tree of good quality. Now it is the producer’s responsibility to ensure that things don’t get derailed further down the road, through limiting damage to the tree, looking after the root system and protecting the trees from drying out.”

Image supplied by Karen Theron | Stellenbosch University.

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