Why are my peach tree branches dying back?

Branch dieback — where shoots or whole limbs wither, brown, and die from the tip inward — is one of the more serious symptoms a peach or nectarine grower can face. It can progress quickly, and acting at the first sign matters. The cause is usually one of three things: silver leaf disease, bacterial canker, or frost-killed wood.

Silver leaf disease

Silver leaf, caused by the fungus Chondrostereum purpureum, begins as a silvery sheen on the leaves of one or two branches. As the disease progresses inward through the wood, the affected branches die back entirely. A diagnostic test: cut a dying branch 15 cm back from the dead tip and look for a brown stain in the cross-section of the wood. If you see it, silver leaf is almost certain. Remove all affected wood to at least 15 cm behind any visible staining, sterilise tools between cuts, and burn the removed material. Prune in summer when the fungus is less active and wound closure is fastest.

Bacterial canker dieback

Bacterial canker caused by Pseudomonas syringae kills shoots and branches from the point of infection outward. In spring, buds may fail to break at all, or young shoots wilt and die shortly after emerging — a symptom sometimes called "blossom wilt and dieback". The bark around dying shoots typically shows a sunken, discoloured lesion. Prune out all affected wood in late summer, cutting to healthy tissue. Spray the whole tree with a copper bactericide in September, October, and November.

Frost damage to shoots

A late spring frost can kill soft new growth overnight. The shoots turn brown and hang limply from the branch before drying out completely. Unlike disease-related dieback, frost-killed shoots have no lesion or staining in the wood below the dead portion — the kill-line is usually sharp and corresponds to the growth that was open at the time of the frost. Cut the dead wood back to a healthy dormant bud. New growth should emerge within weeks in the warm season.

Avoiding wounds that invite disease

Both silver leaf and bacterial canker enter the tree through pruning wounds, broken branches, and bark damage. Always prune with sharp, sterilised tools. Avoid pruning in wet autumn and winter weather when spores are most abundant in the air. Seal all cuts larger than 1 cm diameter with pruning compound or grafting wax, especially on established fan-trained trees where large branches must occasionally be removed.

When to call it a loss

If more than a third of the canopy is dead and a brown stain runs through the main trunk, the tree may be beyond saving. Dig it out, remove the root ball, and do not replant another Prunus in the same position for at least two years. The spores of silver leaf can persist in soil and debris.