Should my apple stay or should it go?

[Filbert]

For the second year my apple tree Fiesta has suffered badly from scab. Most of the fruits have split and I have removed lots of them this year. From what I have read on the vine wet conditions seem to be the catalyst for apple scab to get hold and being in central Scotland the weather is often wet and drizzly, so pretty much always going to be an issue.

My question is : Is there anything that I can do to reduce the chances of severe scab next year or should I just give up with this variety and replace with another more resistant one? (I like the flavour of the apples on the few that are edible.)

[SarzWix]

Depends how much effort you want to put in? If you want to save it, then you can try to improve the drainage over winter by adding sand and grit/gravel to the soil around the roots, but, this will disturb the roots enough to set back the cropping for a year. I have seen it done successfully though, basically by more or less lifting the tree and putting gravel underneath it, grit and sand mixed in the soil around it, and then a sort of drainage ditch round the perimeter also filled with gravel.

You could try doing some or all of those things and see if it helps? Or, as you say, you could look for a more suitable variety for the conditions and hope that you like the fruit as much.

[Filbert]

It is quite a wet corner that it sits in. If I move it to a different situation will the scab improve or is it the moisture in the air that does the damage?

[SarzWix]

As far as I know, it's having the roots too wet, although someone else may come along that knows better than me

[FB.]

Scab is caused by water remaining on the surface of fruits (or leaves) for several hours. The fungal spores germinate and grow in the droplets of water after several hours of wetness.

Moving the tree to a sunnier or faster-drying spot might help, but it sounds as if your area is so damp that you need a tree with very strong resistance to scab. Fiesta has only slight resistance to scab.
I have noticed a possible connection between rootstock and scab, with some rootstocks seeming to help resist scab (perhaps by better ability of the roots to absorb something from the soil, or perhaps a naturally-produced anti-fungal substance). For those who consider that to be a crazy idea, consider that the MM rootstocks are used to give an apple tree some resistance to woolly aphid; if rootstocks can give aphid resistance, then why not scab or other resistances?

But it sounds as if either you'll have to spray, or the tree will have to go.
If the roots are well-established, you could try re-grafting the tree to another variety, retaining the main structure of your tree, but grafting new tips to the branches, using a more scab-resistant variety.

Interestingly, my Fiesta only gets occasional traces of scab on the fruits which mostly heal over by themselves - but I get a lot less rain here.

In some of the wetter parts of the UK, it can be difficult for any apple variety to resist diseases such as scab or canker - and even if you find a tree that is resistant to those diseases, it may not have much frost resistance.

Trees that I'd try in wet, scab-prone conditions (in alphabet order, with special resistances noted):

Belle de Boskoop (scab, canker)
Crawley Beauty (scab, canker, frost)
Discovery (scab, frost)
Edward VII (scab, frost)
Newton Wonder (scab, canker)
Red Devil (scab, frost)
Saturn (bred especially for very strong resistance to scab)

But even the resistant varieties can suffer from such heavy rainfall and such massive spore load that they still get infected by scab. Resistance is like armour plate; hit it hard enough and it will still fail.

[FB.]

Some more with good scab resistance:

Annie Elizabeth (scab and canker)
Egremont Russet (scab, canker and frost)
Grenadier (very strong resistance to both scab and canker)
Reverend Wilks (scab and canker)


Quite a lot of the russet type apples have good resistance to scab on the fruits, but may get scab on the leaves and suffer reduced vigour.

[chrisguk]

Just to tune in a bit, my Fiesta always seems pretty much untouched by scab, and i live in the North West.
It's grown on an M26, so as FB, maybe it inherits some of its resistance from that?

It's rather gangly looking, so it does get plenty of fresh air all around, but apparently all Fiesta look this way.

[FB.]

Chris

Yes, from what I've seen with my apple trees, M26 seems to slightly help resist scab, whereas M25 seems to slightly reduce the scab resistance of whatever is grafted onto it.
On the plus side, M25 seems to increase mildew resistance and frost resistance of the blossom of the variety grafted - although the M25 part itself may suffer lower-trunk bark/canker problems caused by deep freeze injuries in mid-winter.
On the other hand, M26 is prone to woolly aphid (aphids are less of a problem where heavy rain can wash them off!). But for woolly aphid resistance, we have the MM106 or MM111.
MM111 is a great rootstock in many ways - it will tolerate conditions that the other common UK roots won't survive - deep freezes, periodic flooding, droughts, shallow/poor soil. Unfortunately, MM111 has a long juvenile period, so crops will be light or non-existent for 5-10 years. The downside is that MM111 seems to increase the risk of bitter pit.

[FB.]

I would like to emphasise that rootstock effects are often only slight.

I certainly wouldn't recommend grafting onto M26 rootstock specifically in the hope of gaining some scab resistance, although it is a minor bonus to consider. However, I am only commenting from my observations on my trees on my soil and in my climate - which may not be representative of other peoples trees.

As I mentioned in my posting above - think of resistance as layers of armour. No matter how much armour you have, there will be occasions where the armour may fail under the strain. However, the more armour you have, the less likely that it will fail under stress.

[Filbert]

Thanks for all the advice. I think I will try moving the tree to another spot and see if that helps. Will also have a hunt round for an apple day to try and taste some of the suggested scab resistant varieties as a fallback. Any info on upcoming apple days within reasonable distance of Edinburgh would be much appreciated.