John Wilton
With the market coming under pressure and the need to improve fruit colour and quality, there is increased interest in grafting as a rapid and capital efficient way to change varieties.
Recently we have seen some very successful conversions of older, more widely spaced trees, to more modern intensive systems by converting single leader semi-intensive trees to multileader “V” systems. These systems rely on grafts being done low in the trunk, usually around 25 to 30cm above ground, which means it is not practical to retain a sap drawer while the grafts become established.
Experience shows it is possible to graft successfully without sap drawers, provided the tree is still dormant, or at least the job is completed before green tip occurs.
Apart from the two to three-week window immediately prior to green tip when it’s possible to lift the bark, cleft type rather than rind grafts must be used for dormant grafting.
With cleft grafts the stump is split so the scion can be inserted into the stump. The graft needs careful positioning in relation to the cambium layer, i.e. the margin between bark and wood, to obtain good contact between their respective cambium layers.
Going from single leader to multileader systems results in rapid return to production, with much calmer, more easily managed canopies too.
These modern multileader canopies, however, need very good support trellis for the new grafts and to enable significant early crops to be carried.
Support structures are expensive, but necessary for success.
When it comes to grafting, health of the orchard is very important.
Field experience indicates that some varieties take grafts better than others.
Silverleaf has been shown to be the major disease problem with grafting. Care must be taken to protect wounds at all stages to minimise its entry during the grafting process.
Silverleaf is endemic in some older orchards of certain varieties so grafting them is considered high risk. Generally, older Royal Gala types do not graft well due to silverleaf. Avoid these blocks.
Virus infection can also be a problem with certain Scion varieties which express virus symptoms e.g. Scired, which is very susceptible to rubbery wood or Royal Gala types, and Fuji that are sensitive to apple mosaic.
Most trees planted over the last 25 to 30 years are likely to be virus free unless contaminated by use of infected scion wood sometime in the past.
It’s time to begin grafting now.
