apple rootstock lumps

Can't say for sure but it like you say it looks like roots trying to form above the ground. I've seen it before on other plants but not apples. Was the soil level higher recently from a mulch or similar?

This is present on a few of my trees, and seems pretty much harmless, i wouldnt let the scion root though if it tries.

As already said: they're roots trying to grow just above ground.
Rootstocks are selected for their ease of rooting - and they can be a bit enthusiastic in autumn, when most trees put out a mass of new roots (using the summer's energy as the leaves are about to fall) and often, on young apple trees, there will be some rough, knobbly or pinky protrusions from the damp part of the bark near ground level.
They are normal, and are not a sign of disease and are not usually a problem, but keep an eye on them to be sure that they don't get infected with canker - although in my experience, M26 (and M9, MM111) is fairly resistant to cankers and rots of the rootstock, while MM106 (and M25) is somewhat susceptible.

With M26, you'll also find that the tree often forms a large bulge at the graft site.

Thanks all for the updates. I was thinking a bit more about this and the tree itself is in a corner of the garden which can be a bit dry. I tend to to use a soaker hose for a few hours during periods with less rain but i might think about sinking a pipe down in to the earth nearer the base roots during the dormant winter period. I guess if it's rooting at a very shallow level due to drought then it might give me problems later on.

You mentioned FB. about canker. I guess there's not much I can do to prevent this except possibly feed, water and keep the tree generally healthy?

M26 isn't too badly troubled by canker in my experience (although the variety grafted on top will have its own canker resistance/susceptibility independent of the rootstock).

If you're worried about canker, you can use Bordeaux Mixture, which is readily available for just a few £'s at good garden centres, nurseries and the like. Bordeaux is nasty stuff (toxic to many creatures, potentially irritating to skin and eyes as well as being corrosive), so follow the instructions carefully. The instructions will probably advise applying around this time of year, so if you wish to use it, you need to prepare to do it soon.

Canker prefers wet conditions - including excessive watering; during autumn and spring, the ground has enough moisture. Only during summer drought will watering be necessary. In droughts, it is better to give occasional deep waterings than numerous light waterings. Constant wetness at ground level or on the lower trunk will cause canker or other rots.

Trees that have been fed too much nitrogen are more at risk of canker.

Young shoots are at most risk of canker. Older wood toughens up and becomes more resistant.

Bark wounds, frost damage, bark rubbing, woolly aphid damage, branch "crotches", leaf scars and the edges of "burr knots" (aerial roots) are the most likely places to find canker.


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Regarding rooting: I dont think that the burr-knots are a sign of drought or shallow rooting - they're a sign that the tree is actively sending out roots all over the place, in search of water. I wouldn't make any changes to the way that you're growing the tree.
An apple tree will always try hard to adapt its root system to the available water supply and once established, the tree will grow or discard roots as it sees fit.
A drought-stressed tree will simply adapt to the environment by spending a couple of seasons growing a larger root system. The tree *appears* smaller as a result, but, in fact, it is larger below ground.
In good soils, apple trees may be 1/3 roots, 2/3 branches - and perhaps 20ft tall with a 10ft deep root system.
In poor soils, the same apple tree may be 2/3 roots and 1/3 branches - and only 10ft tall but with a 20ft deep root system.

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thanks again FB. Encyclapedic knowledge as always.

I'll probably try and do without the likes of bordeaux mixture for now and take my chances. According to the information on the nursery's website that particular variety doesn't appear to be suseptable to canker.

The variety and the rootstock will only have a slight effect on each others disease resistance - and maybe no effect at all. Sometimes the two parts of the tree interact in unpredictable ways.

This year I lost a handful of canker-resistant apple trees (Annie Elizabeth, Belle de Boskoop, Brownlees Russet among them). They were killed by cankers/crown rot that attacked their hard-winter-frost-damaged M25 rootstocks. The disease "hit below the belt", so-to-speak - with the disease getting into the bark that had been damaged by freezing and thawing of the ice and snow around the tree during the vicious winter.

I have lost a number of M25 and MM106 trees to rootstock cankers, but not yet lost a M9, M26 or MM111.
You'll probably be OK with your M26.

Out of interest, which variety do you have on your M26 rootstock?

The variety is Sunrise (The 1990 canadian one). We also had a serious winter. with 5 solid weeks of snow cover then a brief thaw then another 3 weeks of it. It went below -15c a few times. I only planted this tree along with a couple of others in mid December (whilst it was snowing) and half expected problems with them as they came from a nursery in Kent. It turned out that everything survived and have had a good year of growth. I was a little bit concered with my "burr-knots" as i've not seen the like before. I currently have 5 trees on M26's; Sunrise, Elstar, Scrumptious, Fuji and Braeburn. The last 2 are experiments as they're not suited to northern climates and are known to be disease prone. Last year the braeburn and fuji had scab but have been clean this year. This winter I'm also going to plant out a potted James Grieve (M26) which I rescued from B&Q at the weekend for £4.98.

Sometimes you get lucky with disease-prone varieties.

Apple diseases tend to adapt to attack the varieties that are commonly grown in a given area. An apple from the USA that has a bad reputation for disease "over there", may be very resistant to the UK strains of the disease.
Many of "our" varieties, when sent to the USA, have a much higher rating for disease than when grown in the UK.

Sometimes a variety is so unusual in a certain area that the diseases are not well-adapted to attack it, so it *appears* to be resistant - at least until the disease has had a chance to start to evolve by mutations. The more trees of the same variety together, the more likely that one will be colonised by a mutant that is well-adapted to attack it, and then it'll pass the disease on to the others, which then contaminate the whole nearby environment with billions of fungal spores.
Twenty trees of one type in a close area will soon succumb to the same disease, which adapts itself perfectly to attack them. (if it didn't adapt the disease would become extinct).
Twenty trees, each of a different variety (especailly if the varieties don't all come from the same family line), make it impossible for diseases to perfectly adapt, so the trees, as a whole, will suffer less disease.

Also, in the nursery, trees are treated with chemicals to control diseases. Unfortunately, these fungicides also kill the "good fungi" that can often compete with - or even kill - apple disease-causing fungi, such as scab.

When fungicide sprays are stopped, the first few years can see the tree badly diseased - especially by scab.
If it survives the first year or two, it often gets colonised by "good fungi" from nearby apple trees or the environment, which may then start to give it some resistance to the disease-causing fungi.
Some varieties considered to be "disease prone" can actually be quite resistant once they've got their normal fungi back.

Talking more about disease resistance.......

Many modern apple varieties have been bred to include the Vf scab-resistance gene.
This was done by crossing regular varieties (e.g. Golden Delicious) with the crab apple Malus floribunda - a crab apple that contains many genes that give very strong natural resistance to just about every major apple disease. In fact, Malus floribunda was immune - untouchable - by the apple scab disease.

However, vast orchards of these Vf-resistant apples were planted throughout the world. Many were planted in wet regions, where their scab resistance was essential.

As expected, eventually the scab fungus appeared to have mutated and there are now one or two "strains" of scab that seem to be able to defeat Vf resistance like a hot knife through butter.
However, these scab strains are not very good at attacking other apple varieties.
Although the Vf scab resistance can apparently be defeated nowadays, the Vf trees still have resistance to most other strains of scab, while the Vf-specific strains of scab are not very good at attacking regular apple varieties.

The following is just my opinion - from experience.

Fruits get more resistant as the season progresses.
If a rootstock that induces early flowering is used (MM106 in particular), the fruits may be that bit more mature before the temperature gets warm enough to reach scab's optimum for infection. Being a bit more mature will make them a little more resistant to scab on account of thickening skins.
M26 rootstock also seems to slightly improve scab resistance. I am not sure whether it is due to superior nutrient uptake, or due to M26's very slight tendency for early flowering.
Of course, early flowering brings the risk of frost damage, although frost-resistant varieties exist.


One reasonably good way to defeat scab is to grow russeted varieties of apple.
The russet seems to protect the apples in several ways:

1.
The outer "russet" of the apple is actually dead skin, which is less nutritious to any scab spores that try to penetrate.

2.
The outer "russet" makes the skin tougher and more difficult for scab spores to penetrate.

3.
The "russet" is actually slightly porous and for the same reason that russets can shrivel in storage (the shrivelling actually improves their flavour), they can also absorb some surface water off the fruit through the semi-porous russet coating - and since scab requires surface water to germinate, the russets dry out faster, giving the scab less time to attack, since scab spores require water on the fruit surface for several hours or more, for their initial penetration into the apple.

4.
Some apples have dull/matt skin finish, which, although it is not true russet, it seems to function like a fine russet, allowing water to absorb, and causing fruits to dry more quickly after rainfall.

5.
In addition, some apples have thicker skins, which may mean that the fruit dries before the scab fungus has fully penetrated into the apple.

6.
Some apple varieties have multiple minor genes that work together to defend against scab. Although these minor genes do not make the apple completely immune, they are better able to defend adequately against a wide range of scab strains, unlike the Vf resistant varieties that have a single strong gene for defence.

7.
Some apples have a "yeast" "bloom" on the skin. I believe that this improves scab resistance by competing against the scab spores - although persistent heavy rain may wash off these natural yeasts/fungi.

8.
Some varieties have some other gene, rather like Vf, which gives resistance.



Many apple varieties have one or more of the above mechanisms that give a little more tolerance to scab.
However, some areas are so wet that no variety will be 100% scab-free.



Some examples:
Points 1-3 are reminiscent of Egremont Russet or the other russets. The fruits are very resistant to scab, but the leaves have no resistance.
Clearly, the fruits have something that the leaves do not, which gives the resistance.

Point 4 is reminiscent of Tydeman's Late Orange.

Point 5 is reminiscent of Winston or Norfolk Beefing.

Point 6 is reminiscent of Discovery.

Point 8 is reminiscent of Edward VII.

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Here we go....I pulled out some old articles on scab.

Belle de Boskoop was immune to attack by scab originating from Spartan and was resistant to attack by scab originating from James Grieve.

James Grieve was fairly resistant to attack by scab originating from Belle de Boskoop and Spartan.

Spartan was fairly resistant to scab originating from Boskoop or James Grieve.

Miller's Seedling was very resistant to scab from any other variety tested (although there will be strains of scab out there that were not tested, which might break through Miller's resistance).

Cox's Orange Pippin was susceptible to scab originating from a wide range of other UK apple varieties.

Worcester Pearmain, James Grieve and Laxton's Superb were fairly resistant to attack by scab originating from Cox's, but slightly susceptible to scab originating from Edward VII and very susceptible to scab originating from each other.

Edward VII was very resistant to scab originating from any other variety, although a highly-virulent strain of scab can attack Edward VII and most other varieties.

If the varieties were left for long enough, certain strains of scab would die out (or be out-competed) in favour of each variety's well-adapted strains.
the highly-virulent Edward VII strain would gradually die-out on other varieties, in favour of their better adapted strains.

Confusing, isn't it?

Many varieties have partial scab resistance - which protects from scab that has adapted to other varieties. Yet other varieties have russet, matt or thick skins that seems to add a little extra scab protection against all scab strains.
Take a look at your own trees and search for little "bleached" pinpoint spots on the leaves (on unsprayed trees, there will be dozens of spots on every leaf). It is my belief that each of those tiny "bleached" spots is a defeated scab attack.
The brown spots will be scab attacks that succeeded in getting past the trees defences.

Varieties that have been grown extensively in commercial orchards (or wet areas) will tend to have scab strains that are well-adapted to attack them.

You can also buy in mycorrhizal fungi , I use biovam mostly o grapes, but also on the apples I'm keen to give the best start to