Gummosis and canker can affect all stone fruit trees – here’s what to do
I noticed my apricot tree, despite bearing a good crop last year, had hardened globules of amber-like sap on various branches, with some die-back.
While I wasn’t too worried then, my concern has grown as the condition, known as gummosis, has worsened.
It usually happens for one of these reasons:
- The tree has a perennial or bacterial canker (most stone fruits can be affected by cankers)
- It has been attacked by the peach tree borer
- It has been wounded by winter damage, disease, or physical damage from a gardening tool
- The tree is stressed by environmental factors.
The most likely cause is a perennial or bacterial canker, so anything you can do to prevent bark wounds will help with gummosis prevention – keep away from the trunk when mowing or weeding.
Bacterial canker is caused by two types of bacteria that infect the stems and leaves of Prunus (stone fruit) species. Cankers begin to form in mid-spring and then shoots die back. Shotholes appear on foliage from early summer.
- Sunken, dead areas of bark develop in spring and early summer, accompanied by oozing sap. If the infection spreads all around the branch it will die.
- Gummosis is common from stone fruits and if there’s no dead or sunken bark, it has probably been caused by physical damage or environmental stresses
- Shoots may fail to emerge or die back suddenly.
- Small brown spots appear on leaves which later fall out, hence the popular name of ‘shothole’
Treatment and prevention
Remove the diseased bark: Cut out the darkened area of bark, until the wound is surrounded by healthy bark. Let the area dry or paint with wound paint. Keep checking the would and repeat the bark trimming if necessary.
Summer pruning: Carry out all pruning in July or August unless absolutely necessary – this will also minimise the risk of infection by spores of the fungus causing silver leaf disease. Don’t compost the prunings.
Plant wisely: To avoid environmental damage, plant new trees in the best sites to avoid frost and wind damage in winter and ensure well-drained soils. All varieties can get cankers but some have a degree of resistance.
Treat your tree well: Try to avoid damage by waterlogging or drought, two major stress factors. Mulch the tree well in spring and feed but don’t let mulch touch the bark.
Tools: Always use sharp and CLEAN pruning tools so you’re not spreading infections and spores.