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Apple Canker - Solution Guide

Apple canker is a disease caused by the fungus Neonectria ditissima, which attacks the bark of apples and some other trees, causing a recessed area of dead bark and eventually the death of the branch. New cankers typically form in mid-spring, and once formed are present all year.

Apple and crabapples are important hosts, although about 60 species of trees such as Alder, Birch, and Poplars are also attacked and even less frequently are Sorbus, Ash, Beech, and many other tree types.

Symptoms

Cankers are typically round or oval areas of dead, hollow bark tissue. They often start at a wound or a bud.

On small branches and fruiting spurs: The infection may girdle and kill the stem in a single season. The bark often flakes off of infected smaller twigs.
On larger branches: Cankers are perennial, with the affected areas covered with dead bark that shows concentric rings indicating periods of active spread/growth. Older cankers lose the bark, exposing dead wood in the center. Perennial cankers develop raised edges as the tree's bark attempts to grow back over the exposed area. Eventually, the branch will die above the canker, progressively weakening as the bark is killed.
On fruits: Developing fruits are sometimes attacked and will rot and then fall off.

Management

Non-chemical controls

Apple canker is usually more severe on trees planted in wet, heavy soils, or acidic soils. Therefore, check, test, and adjust the soil composition before planting to provide proper percolation.
Test for pH if symptoms develop and follow recommendations for lowering pH as necessary.
If fungal symptoms develop on spurs or limbs, remove all infected smaller branches using proper pruning techniques. With larger limbs, removing all brown, callused bark or wood back into fresh green tissue is essential. For Apple canker, this pruning is best done on a dry day during the summer rather than waiting until dormant season as you would for Fire Blight or essential annual corrective pruning.

Fungicide Treatment

After pruning, treating with fungicide like copper, sulfur or Bonide® Captan® can be a helpful preventative for reoccurring cankers.
Always read and follow all pesticide product label instructions for mixing and use.