Some apple trees are susceptible to infection by canker – rough lumpy areas on the trunk or branches. Cox’s Orange Pippin is one of many trees that seem to get infected with this disease.
It is caused by a fungal spore entering the bark. The first signs are usually leafless twigs or twigs with small shrivelled leaves.
Closer inspection will reveal cracks in the bark – exuding a sticky substance, or at the later stages of infection, lumps – best described as carbuncles!
Canker can also spread to the fruit - resulting in the fruit turning brown and dying on the tree - or sometimes emerge during storage.
It is probably the most serious of all apple tree diseases, and often left until it is too late to do anything.
The fungus spores of Apple and Pear Canker usually enter the tree bark from pruning wounds and other damages – even damaged fruit. It is also more prevalent where the tree is suffering other stress symptoms – maybe as a result of waterlogged soil, or lack of feed, leading to a general demise of the tree’s health.
Once you start to notice Canker disease, it will have already taken hold beneath the bark. For it is out of sight where it first starts - just under the bark of the Apple tree. The infection then starts to 'lift' the bark, and the infected wood can be seen beneath. The affected area of bark will show white or red spots or pustules of the Canker Spores.
There are chemical controls, but physical attack is the first
option for badly infected trees.
Cut out the affected areas on small branches with a sharp knife – or remove the branch completely. Make sure that you cut back to clean wood, and that there is no infected (brown) tissue left in the area.
Larger ‘carbuncles can be cut away with an axe – if you are used to using one – or a hammer and chisel.
ALL cut off sections should be burned, or sent to rubbish in sealed container. Do NOT try to compost these cut offs. Paint the cut away areas with Canker paint.
Badly infected trees are probably best removed, as they
rarely get back to full health. It may take a few years for the tree to die from
a bad infection of Canker, during which time it will realease spores to affect
other trees in the area. The spores are easily carried by the wind - or even
rain splashes from infected fallen leaves.
Proprietary Bordeaux mixture can be used as a preventative, or to help contain the spread of the disease. Apply twice in the Autumn – right after fruit picking, and then again as the leaves start their autumn colour change. Treat health trees as well as those infected with Canker disease. Dithane 945 can also be used to control and contain Canker disease in the early stages, as can Mancozeb. Read the manufacturers' labels before use.
The spores can overwinter on fallen leaves, so cleanliness is also important. Again, do not compost the leaves from trees affected by Apple Canker.
Apples that are resistant include Lord Lambourne, Discovery, and Ellison’s Orange. If it is a particular problem in your area – avoid planting Cox’s Orange Pippin – Sad!