University of Maryland Extension

Graft Failure and Normal Graft Bulging - Trees and Shrubs

graft failure

Back to Common Problems - Trees and Shrubs

Graft Failure

Graft incompatibility, improper technique, or environmental conditions, may cause graft failure. Graft incompatibility is not clearly understood but may be the result of genetic differences between the grafted parts. Abnormalities may develop in the vascular tissue at the graft union. Disease-causing organisms such as viruses or phytoplasmas are other possible cause of incompatibility. Care should be taken to use disease-free plant material when grafting.

The most pronounced symptom of graft failure is a smooth, clean breaking off of a tree at the graft union. This may occur one, two, or many years after the graft is made. Other symptoms of graft failure include general ill health of the tree or shoot dieback. Foliage may yellow in late summer, followed by early leaf drop. Vegetative growth of scion and rootstock may begin or end at different times. There is often a distinct difference in growth rate between scion and rootstock. Overgrowth may occur above, at, or below the graft union and results in a visible difference in the trunk diameters. Suckers can develop from the rootstock. While it is possible for trees to survive with one or more of these symptoms, a combination of many symptoms may result in premature death of the tree. Weakened trees may have to be removed.

bulging graft
Overgrowth may occur above, at, or below the graft union and
results in a visible difference in the trunk diameters.

Normal Bulging at Graft Union

A slight bulging, swelling, or "crook " in a tree trunk, two to three inches above the soil line, is the result of normal healing at the graft union. Grafting is a method of propagation that joins a scion (upper portion) and rootstock (lower portion) of two similar species of plants. The site where the scion and rootstock meet is called the graft union. Swelling occurs as callus tissue is formed and new vascular cambium tissue develops in the callus bridge area. The graft union should remain above the soil line to prevent the scion from developing roots, losing the influence of the rootstock.

normal bulging graft union

Nurserymen frequently use grafting as an excellent way to propagate plants not easily grown from seed or cuttings, especially cultivated varieties. It allows the grower to produce a saleable plant more quickly. This technique allows nurserymen to select and control desirable plant characteristics such as growth habit, growth rate, size, hardiness, and time required for fruit production.


    
        

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