Friday, 26 August 2011

Recognising and treating Canker on Apple trees 

Fungal Canker is a common problem on apple and pears especially in the wetter west of the U.K.
It will infect young twigs in the Spring and cross infect to older wood, it can infect the trunk and rarely it will kill a tree. On the positive side older trees badly infected will often fruit well, as the tree is put under pressure where the sap flow is constricted, it can infect fruit and effect storage qualities.

Look out for young stems/leaves dying back, this was in July but it can occur from Spring onwards

Stem infection is more noticeable in wet weather
The stem becomes constricted and growth beyond dies back 
The cure - a multi - pronged attack is required

1.Recognise and remove on a regular basis, in the west of Britian check trees monthly, remove any infected wood  cutting back a foot from the infection at least. Burn the wood removed, treat cut surfaces either with 10% bleach, or use armillatox from a garden centre, or rub wound with soil[this contains so many competing organisms the fungal canker is crowded out]. Treat secateurs with 10% bleach  dip between cuts.

2.Encourage strong hard growth, regular pruning of apple and pear trees rejuvenates trees and keeps them healthy, though excessive winter pruning will give too much growth and little fruit. Summer pruning is good in August to encourage fruiting and remove unwanted growth.
Dont overfeed apple and pear trees with fertiliser, or even manure, as this encourages sappy growth prone to canker infection.

3.Apply Lime, calcium applied in the form of ground limestone or garden lime encourages hard growth resistant to infection. It also improves fruit storage. On sandy soils apply lime every year on clay soils every other year. For a young tree a few years old a few good handfuls, for a large mature tree half a bucket. Sprinkle a handful of lime on the soil used when backfilling around a newly planted apple tree.

4.Choosing the right tree, some varieties are more susceptible to fungal canker than others. Bramley has been shown to be resistant, Spartan more susceptible.

5.Live with canker under control,doing all of the above will greatly reduce fungal canker and keep trees healthy. Older trees may have a lot of infection that cannot easily be pruned away, though paring with a sharp knife and treating as above [point number 1.] will help. In the long term keeping older trees and living with canker can be more acceptable than loosing the tree, they maybe fruiting well. There is evidence that trees will heal over cankerous wounds.


  1. Use a lot of lime in restoration building here in north west. Can you use old lime mortar / building lime?
    Thanks for canker suggestions (we suffer badly) and for great trees which are all doing well!

  2. Building lime is generally hydrated lime or quick lime which is pretty soluble and though quick acting and can cause damage to roots, and to the soil. Garden lime which is ground limestone is best, as it is less soluble therefore releases slowly in the soil and lasts longer.

  3. Thank you for this - though we use some hydrated lime it's mainly lime putty...and never quicklime. But will certainly use garden lime for your trees, and old lime putty to prepare overwintering bits of the veg garden.

  4. Have you an suggestions for a good winter wash? We used to use tar oil wash but understand that it's no longer approved?

  5. Winter wash has gone out of fashion and rightly so.As fruit growers have become more conscious of beneficial species that overwinter on fruit trees they realize it is better to preserve the ecosystem that naturally keeps pests under control. Ladybirds, and typhanadromid mites are two examples of useful predators that overwinter and would be killed by tar oil washes.