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Many woody ornamentals and most fruit trees are propagated by grafting. Sometimes the graft union fails, resulting in the main stem breaking off, dieback, poor growth or death of the top part of the plant. In contrast, the root system will often remain alive and may send up suckering shoots.
For various reasons, such as ease and speed of propagation, disease resistance, tolerance to certain conditions and for the control of vigour (predominantly in fruit trees), a large proportion woody plants are propagated by grafting and budding.
Unfortunately, the graft union sometimes ceases to function at a later period, possibly some years after planting. When this happens, the flow of nutrients from the rootstock to the top growth (scion) becomes limited or stops completely and the top growth will gradually or suddenly deteriorate.
The affected plant may start showing signs of poor growth and gradual deterioration; on the other hand, the demise can be quite sudden. Graft failure can occur in both young and fully-established plants with little prior warning.
Remember, similar symptoms can be found on plants affected by bacterial diseases such as crown gall, which can cause decline of grape vines, roses and other trees and shrubs. Bacterial canker is also a common problem on both ornamental and fruiting Prunus. Death of woody plants can be caused by root diseases such as honey fungus or Phytophthora.
In addition, establishment problems may be to blame for poor growth of recently planted trees and shrubs.
When buying plants select, healthy, strongly-growing specimens. Check the graft union carefully. It should be neat, well callused over (joined) with no signs of decay or suckers being produced from the rootstock.
Avoid mechanical damage to the graft union during transport, planting and in the plant’s final position, including accidental damage from strimmers and lawn movers.
Avoid over-deep planting. In the majority of plants, the graft should stay proud of the soil or be positioned just below the soil level (roses). One of the exceptions are tree peonies where the graft should be below soil level.
When mulching, keep the base of the plant free from much.
Graft failure occurs when the rootstock and scion become partly or fully separated and/or an impermeable, often corky, layer forms between the rootstock and the scion. However, it is often difficult to establish the exact cause.
Graft failure can be caused by factors such as:
Graft incompatibility can occur for number of reasons, including:
Phytoplasmas are single-celled organisms and, as opposed to bacteria they lack a cell wall. Previously known as ‘mycoplasma-like organisms’ or ‘MLOs’, they live as parasites of plants and cause symptoms that are similar to viruses. As with viruses, there is no remedy but to replace infected plants.
Bacterial cankerBrown leaves on woody plantsCrown gallEstablishment problemsHoney fungusPhytophthoraTrees and shrubs: plantingWhy has my tree or shrub died?Wisteria
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