Cankers may be either bacterial or fungal. It is the fungal form that affects apples and pears. Fungal spores enter via pruning cuts, wounds or cracks in the bark. Canker can be very destructive if left untreated.
FUNGAL CANKER DAMAGE: Areas of bark can split, hollow and discolour or crack in concentric rings. The infected area can swell and will have little or poor growth around the affected area. Fungal growths may appear, which can be creamy/white in the Spring and Summer, Red in Autumn/Winter and whole branches may die back.
TREATMENT: Prune out all infected wood and destroy this.
BACTERIAL CANKER (also known as Bacterial leaf spot) This is a serious disease that needs swift action to prevent it spreading and ultimately killing the tree. The bacteria usually enters in the Autumn via cracks in the bark, wounds or pruning cuts but it can also attack new shoots and leaves in the Spring. Young trees are most at risk, especially if the weather is damp or windy. Bacterial canker can affect any stone fruit.
DAMAGE: Bacterial canker causes small dark spots in leaves that turn into round holes. The leaves will subsequently turn yellow, wither and die. Buds do not open, branches dies back and affected areas of bark may become sunken and/or ooze orange resin or gum.
TREATMENT: Prune out and destroy all infected wood, taking out whole branches if necessary. Disinfect all tools used.
HOW ARE DISEASES SPREAD? Most fungal infections are carried by spores being blown, from one plant to another by the wind, or transmitted in water splashes. Bacterial infections are spread in the same way although insects can also carry them. Viruses are transmitted by sap-feeding insects, especially aphids.
PREVENTING DISEASE Plants are most at risk when they have just been pruned or are damaged. It is imperative to prune at the correct time of the year – Winter season (when the tree is dormant (lost all of it’s leaves)) for fruits with a pip; apples, pears and quinces. Growing season (July/August even if fruit is on the tree) for stone fruits; apricots, cherries, gages, nectarines, peaches and plums.
Do not overcrowd trees Make sure they are planted with sufficient space between. Free-standing trees should not be planted near fences/walls/buildings etc.
Weed, water and feed your trees The healthier your tree is the more resistant to infection and disease it will be.
Disinfect tools Before and after use, especially when pruning.
Dispose of infected matter Clear all windfalls, pruning and any infected/diseased leaves. Burn or remove from site rather than composting.