Pruning advice: tree paint or sealer
The traditional practice has been to paint over pruning cuts with anything from left-over house paint to specially formulated antiseptic tree pastes. The theory is that the paint seals the wound and prevents the entry of water and disease.
Some horticultural experts question this practice as trees, especially resinous evergreen conifers, quickly seal off wounded areas and heal by themselves. They say that it is important to make the cuts in such a way that water does not pool on the surface. Plus if you begin training a tree when it is young, you can avoid the large pruning cuts which a tree can struggle to recover from.
Sheryn Clothier, NZ Gardener columnist and former editor of the Tree Crops Association journal, is one who says no to pastes and sealers. She says that when pruning is done correctly, the tree needs nothing else.
"I want to emphasise the word 'clean'. Pruning is surgery," she says. "Using clean tools is paramount. Sterilise tools between cuts, and most especially between trees by dropping into a bucket of bleach solution or wiping down with meths-soaked cloth. This is much more important than adding a sealing paint as the tools can carry fungal or bacterial disease from one cut -- straight into the capillaries before the tree has time to enforce it's natural defences -- into the new cut."
Other experts argue that older, deciduous trees may not be able to set up defences quickly enough so sealing paint or paste should be used in these cases. In particularly, fruit trees can be vulnerable to bacterial diseases so these should have cuts sealed especially in humid conditions.
Fruit tree expert from Waimea Nurseries Kate Marshall says she is a big supporter of using pruning paste such as Yates PruneTec Sealant for fruit trees, as these trees can be susceptible to disease infections which enter the tree through pruning wounds.
"Fungal and bacterial diseases like silverleaf and bacterial blast can be devastating for stonefruit trees, especially an infection in the trunk which can cause the tree to decline gradually and even die," she says. "Painting a small amount of sealant on the wound will help to avoid the infection. It's a small insurance policy on a tree that can be very long lived, and often we have waited a few years to start bearing fruit. Often fruit trees are pruned in winter which is a period of high risk for infection, making the sealing even more important."
Kate, who is also a columnist for NZ Gardener, maintains that thanks to the use of pruning paste, Waimea Nurseries now has "very few issues" with silverleaf and bacterial blast.
To avoid any disease being introduced when you prune, follow these steps:
* Prune only in dry, warm conditions, to prevent airborne infections.
* Make cuts on an angle such that future rain will drain off.
* Clean any sawdust off the cut and cut out any damaged or diseased wood.
* If you do use pruning paint or sealer, then shake well and apply with a clean brush or an aerosol spray to the clean, dry surface as soon as possible after pruning.
- NZ Gardener