SLOG Canker Survey – report by Adam Rubinstein, January 2017
There were 98 responses to the canker survey which, although a relatively small sample, has produced some interesting, if inconclusive, results.
There certainly appears to be a tendency for apples grown on MM106 rootstocks to be more susceptible to canker. There is also a strong suggestion that some apple varieties are more susceptible.
Of the different rootstocks there seems to be a different pattern of susceptibility. MM106 is more vulnerable when very young and, if it survives the first few years, is then likely to stay OK.
M25 seems resistant at first but older trees, particularly those that have been neglected and not fed for many years, can then become much more likely to succumb.
The most surprising result is that MM106 seems to be significantly more susceptible when drainage is better. However, this may be coincidence or due to poor survey interpretation.
Question 1 Exposure
Marginally greater canker on exposed trees but not significantly so apart from MM106 where 75% of exposed trees had either manageable or bad canker, compared with 44% of trees in relatively sheltered positions.
Question 2 Drainage
Drainage seems to affect the different rootstock differently, although the numbers in the survey are too small to be conclusive.
Poor drainage has the greatest effect on M111 rootstocks with 75% having canker to some degree on poorly drained soil against 12.5% on well drained soil.
Most surprisingly, the sample showed that MM106 rootstocks do better on badly drained soil (28.6% with canker) than on well drained (66.7%)
M25 rootstocks show very little preference at all.
The dwarfing rootstocks were too small a sample in this question to draw any useful information as only 1 was on poorly drained soil.
Question 3 Soil type
MM106 significantly worse on acid soil and loam than on alkaline soil but there was only a very few on alkaline soil so not conclusive.
M25 significantly worse for canker on alkaline soil than acid.
M111 no useful results for this question.
Question 4 Mulch/feed
In general, the results show that feeding your trees tends to make them less susceptible to canker. This is most apparent with M25 trees where over 70% of those trees that are never fed have either manageable or bad canker. MM106 seems less affected but the small samples reduce the significance of this result. Similarly M111.
Question 6 How much canker?
Dwarfing rootstocks: 6 trees with canker, 10 without
MM106: 18 trees with canker, 12 without
M111: 5 with canker, 1 without
M25: 10 with canker, 9 without
Unknown/other: 16 with canker 6 without.
Question 8 varieties
Perhaps most interesting is the difference in susceptibility by variety. The worst, in order of badness are:
James Grieve 25%, Blenheim Orange 18%, Discovery 17%, Lord Lambourne 12.5%, Fiesta 13.33%, Egremont Russett 11.75%, Laxton’s Fortune 13.33%, Court Pendu Plat 12.9%, Irish Peach 10.7%, Ellison’s Orange/Red 10.34%, St. Edmunds Pippin 10% cankered.
None of the following varieties were reported as having any canker at all:
Jonagold, Delcorf, Crawley Beauty, Beauty of Kent, Suntan, Early Victoria, Burr Knott, Captain Kidd, Duchess of Oldenburg, Lord Suffield, Fillingham Pippin, Galloway Pippin, Lord Derby, Bloody Ploughman, Lady’s Finger of Lancashire, Taylor’s Favourite, Greensleeves, Arthur Turner, Golden Spire, Winston, Lemon Square.
There were other varieties with no canker but with less than 4 of each tree, the conclusions are less reliable.
Conclusions.
Due to the low sample numbers we can only hope to start to get an idea of trends rather than expect to draw conclusions from the figures. The hypothesis that MM106 rootstocks produce trees that are more susceptible to canker, in our northern climate, certainly hasn’t been disproved and, in my mind, the results support this theory, particularly on young trees. Trees on M25 rootstocks, however, appear to be more susceptible when they are mature, particularly when they are not fed.
Perhaps the most telling information can be gleaned from some of the many comments added to the survey which make the most interesting reading.
Interesting and relevant comments [With relevant info drawn from the rest of the commenters survey submission]
Out of 38 young (all less than 7 years old) apple trees in total, I have 4 which are suffering from noticeable canker. So only minor surgery has been given - but, as the cankers are, in all four cases serious and apparently growing, it is likely that the trees will have to be destroyed eventually. All four are currently fruiting, quite heavily. The four varieties of mine which have canker are: Red Windsor, Scrumptious, Limelight, Bramley. It's possible that I've missed some small outbreaks of canker on the larger trees, on inaccessible parts. In all the four cases, the canker has afflicted the main stem. [All on MM106]
I lost all this years new MM106 rootstocks to canker (after grafting) and some of the previous years too - the ones that have grown well are canker free - I have a small amount of canker on M26 and M9 but it is manageable.
Worst examples where trees were already planted on the orchard and seem to have been neglected. Those I have planted and been able to monitor I have been able to deal with. I have taken to painting wounds after removing affected branches and this seems to be useful. About to plant new bush trees on MM106 and have tried to select some varieties that apparently have some resistance. [Canker on M25 and unknown rootstocks]
The ones on clay may be more susceptible [Canker on MM106 and M25].
Unsightly cankers and much new growth killed, but trees carry on and crop fairly well anyhow. [Canker on MM106 and unknown rootstocks].
We have one very old tree that fruits every year but has canker on all new shoots. We have four equally old trees with no canker. Each Bramley on M25 has developed bad canker (3 trees) , one immediately, two after 10 years - now so bad as to affect fruiting. Smaller modern desert apples (6+) are canker free so far (10 years). [Poorly drained, acid soil, never feeds]
We have around 320 apple trees - canker has periodically been an issue and has destroyed around 25% of all trees we have planted over the years. Early years (up to say 10 years old) seems to be the time the trees are most vulnerable. [Canker requiring major surgery or destruction of tree on MM106, manageable levels of canker on M111 and M25].
I have about 100 trees on mm106. Canker is variable - mostly variety-dependent. The M25 trees are very young with no signs of canker yet, but early days. [MM106 Very slight or no canker at all, manageable levels of canker, Canker requiring major surgery or destruction of tree. Exposed, acid clay loam, reasonably/well drained. Potash feed annually].
New orchard planted 2006 onwards most of our trees ,16 ,on MM106 - James Grieve the only one lost (in the early years). St Edmunds Russet also sufferring from canker but we are trying to manage it, great taste . The tree is more exposed ie on edge of orchard can catch a NE wind. other trees fine, some slight problems. Annie Elisabeth on M27 is the worst (growing on end of row), 5 others also on same rootstock , fine. [Acid soil, well drained, feed not every year].
I do not think that we have had canker on the trees here yet, maybe because they are all young or on a sheltered well-drained SW slope? Probably not a good trial site to test for canker.
Once they get to a certain size they seem OK ( except the Ribston Pippin )
We have only been here 6 years. Trees we have planted have no canker. Pre-existing trees do. Would be happy for you to visit to take a look.
At least 1 young tree killed by canker in its MM106 rootstock .
The hypothesis advanced at SLOG's AGM recently by Hilary Wilson, viz. that varieties with smoother bark and more leathery, glossy leaves were better able to withstand canker sounded v plausible at first to me; but I cannot make it fit the facts in my own orchard. Andy Gilchrist did say that modern varieties seem to be more susceptible, which seems from my experience to be true, but I do have a definite, severe occurrence on Bramley. I think it is notable that I have Lord Lambourne close (~8ft) to Limelight - the former unaffected, but latter badly affected. Similarly Sunset is close to Scrumptious - the former unaffected, but the latter badly affected. My Bramley is relatively distant from other apple trees. All this suggests to me that the disease is probably NOT contagious between trees. My hypothesis is that canker is caused by the mycorrhizal fungi, or perhaps some other bacterial infection in the soil around the roots, with which the rootstock (esp.MM106) has a symbiotic and sometime positive relationship, is triggered perhaps by excessive dampness, into a destructive relationship with the tree. It seems to affect only the bark & stem; the fruit is unaffected - except possibly when the canker is very severe.
Old trees existing on the property have been affected with canker and none now living having been killed and removed
Jupiter tree (about 3 or 4 years old) was given to me and it developed canker in the first year with me.
Personally. I've had problems losing new rootstock to canker in the last 2-3 years on MM106 mostly and can't understand why - the varieties I would mostly avoid in my locality are Bramley, Pink Lady, Lord Derby, Spartan.
Very wet ground seems to be the problem. I could well understand that rootstock is key, not scion variety. We have managed to graft clean scions from an old cankered tree with no sign of canker (yet) in the new tree
The only apple tree that I have that is suffering from canker is the espalier Bramley on MM106
It is our old trees which have canker the young are mostly immune, my guess is that any of the original planting which were severely affected would have been removed leaving only resistant or immune. [Sheltered, poorly drained, clay loam over boulder clay pH slightly alkaline, feed not every year. Those on MM106 Very slight or no canker at all
Those on M111 manageable levels of canker
Those on M25 Very slight or no canker at all]
We tend to get canker when branches get damaged, like rubbing up against fencing or deer nibbling.
Mature trees seem to cope better. Good drainage is vital
Young trees on 106 rootstocks are susceptible to canker below the graft.
Some trees suffer in youth but not age and vice versa. Cutting out and spraying with disinfectant can work but sometimes it is systemic. Some trees seem to handle quite a lot if canker and yet survive whilst others succumb to moderate outbreaks.
by Adam Rubinstein, January 2017