Page 38 - Simply Vegetables Spring 2024

Apple Canker
Management and Control
The following notes are from a talk I attended at Fruit Focus on the latest research into apple canker and is the current best advice available to help reduce and control canker. This disease can have a major impact
The main effect of canker is that it will reduce the yield of fruit and can slowly encircle the branch killing it and over time spread throughout the tree resulting in the death of the tree if it is weak. As well
on apple crops as it can
both reduce crop yield
and kill the trees over a
period of time if they are
either prone to canker or
poor growers. Canker is
caused by a fungus called Neonectria ditissima, it
used to be called Necteria
galligena in my college
days! It infects wounds, it
will not penetrate healthy
bark so one of the main
controls is not to damage the bark or carry our un-necessary pruning.
Young cankers can produce conidia which are a type of spore that can spread the disease on the tree, on more mature cankers ascospores are produced and these are spread by wind blowing them onto other trees and onto any wounds. Once the spore lands on the wound in damp weather it will germinate and grow into the wood starting a canker which over time spreads to other parts of the tree. At the time of writing this article the weather is very wet and this can lead to bad canker attacks so inspect your trees carefully this summer. The spores need moisture to germinate and infect the tree.
as reducing the yield the canker can affect the fruit causing a post-harvest rot which means the apples will not store for very long.
So, what can be done to prevent and control canker, firstly good hygiene helps to control it. Do not leave infected wood lying around in your garden or orchard, either burn or bin it. Next remove any inoculum in the trees, that is remove
any cankers, so spores are not produced to spread. Prune back any infected branches to 15 to 20cm below the canker to ensure all infected wood is removed; research
has shown that canker can be 5cm further down the stem than the actual canker lesion on the bark. Go through your trees two to three times a year to check for cankers and remove any seen. Applying high nitrogen fertilisers can make cankers worse so only apply balanced fertilisers like Growmore or Fish,
blood, and bone. Orchard nutrition and hygiene are very important and can substantially reduce canker infections.
As well as reducing the yield the canker can affect the fruit causing a post-harvest rot
Canker
Early signs of canker
The researchers are at present looking at new control products for canker and are also looking at biocontrol’s, biostimulants, and defence elicitors. They are looking
at applications to the soil of mycorrhizae and Trichoderma to see if these improve the health of the trees and reduce canker
infection. Soil amendments of arbuscular mycorrhizae has been shown to improve canker resistance in apple trees so more work is being done to see how effect it is. Trichoderma also seems to give some control, as these two substances are natural occurring, they will likely
be approved and available to both commercial and amateur growers: so, one for the future!
Research carried out in New Zealand recommends growers not to prune in the winter and to go through the trees four to five times a year removing any cankers. The quick healing of wounds helps to reduce canker, so they prune in the spring or summer.
One method of reducing canker suggested was applying a hydrated lime spray to the tree and this reduced canker by 50%. The recommended application rate is 5gms / litre and sprayed on at early leaf fall, mid leaf fall and late leaf fall. If this is repeated each year it will greatly reduce canker infection.
After removing any cankers clean your pruning equipment with a 10% bleach solution to prevent spreading the disease.
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One method of reducing canker suggested was applying a hydrated lime spray to the tree