[MickyB]

This year the potatoes I grew were Pentland Javelin, Charlotte, King Edward, Maris Piper & Desiree with the following results......

1. Pentland Javelin, nice first earlies, no scab problems, good crop - happy 
2. Charlotte, second earlies, free from scab to start with, progressively more scab the longer I left them, the scabs were minor and the majority scrubbed away - happy 
3. King Edwards, main crop, not as big as I expected but still adequate, made lovely mash, more scab then earlies but mainly just on surface and removed during peeling - semi happy  :happy:
4. Desiree, nice big spuds but heavily scabbed, not good as chips (trying as mash next) I thought these were supposed to be quite scab resistant?
5. Maris Pipe - untested so far - still in the ground.

Having looked on the internet I think the potatoes have 'common scab'.

The soil is quite sandy did this add to the scab problem?

I tried to keep them well watered but it has been a hot dry summer, did this add to the scab problem?

Should I dig them up as soon as possible, will leaving them add to the scab problem?

Any tips for next year? I have read that alkaline soils doesn't help and adding manure makes the soil more alkaline, should I add manure to next years plot or is this bad information? What new varieties should I try?

I also noticed small yellow worms when digging them up - is this wire worm? One or two potatoes had holes in them but not very many at all.

[Trillium]

Sandy soil is not a cause for potato scab. Mostly, it's already on the potato seed you used, which is why it's highly recommended to use only fresh certified seed potatoes rather than shop or saved potatoes.

Another scab promoter is using the same soil for potatoes within 3 years. The scab will mostly die off in the 2nd year but not always. A 4 year rotation is better for tatties.

Don't make the soil more alkaline as this promotes other potato problems. They prefer slightly acidic soil. Lime is use only on the cut surfaces of potatoes to stop bacterial growth on too large seed potatoes.

Manures do not make the soil more alkaline. They make it slightly more acidic. Potatoes love manure as feed and as a good soil conditioner, especially in sandy soils.

Digging them up won't help much if the potatoes are still small. They'll still have the scab regardless of what you do, but the decision is yours.

There's more info HERE

And yes, that sounds like wireworms you have, mostly a problem on recent grass areas.

[MickyB]

Thanks for the tips. 

The seed potatoes were purchased from B&Q (akin to your Home Depot) I am not sure if it would be better to purchase from elsewhere next year maybe other UK members will be able to advise me better on this.

I have well rotted horse manure that I was planning on using, is this OK or would cow manure be better?

The plot was grassed over when I got it this year so that would fit in with what you say about the wireworm, they don't seem to have caused much damage to the potatoes so hopefully they will not prove to be too much of a problem, I am going to rotate the potatoes around but it will probably be a three year cycle although I could plant in a different position in the same plot to increase the cycle time further.

I don't know about the Maris Piper's but the Desiree potatoes are a good size so I will dig them up, will they store OK with the scab or will they be more prone to rot when stored? 

[Salmo]

http://apps.rhs.org.uk/advicesearch/profile.aspx?PID=230

[Trillium]

  Salmo, that's the same link I provided.

Normally scab doesn't get worse in storage as it's mostly a cosmetic thing.

We use cow manure because that's what we can get but I'm sure horse will work just as well (no horses around us).

[Becky-Lou]

This year the potatoes I grew were Pentland Javelin, Charlotte, King Edward, Maris Piper & Desiree with the following results......

1. Pentland Javelin, nice first earlies, no scab problems, good crop - happy 
2. Charlotte, second earlies, free from scab to start with, progressively more scab the longer I left them, the scabs were minor and the majority scrubbed away - happy 
3. King Edwards, main crop, not as big as I expected but still adequate, made lovely mash, more scab then earlies but mainly just on surface and removed during peeling - semi happy  :happy:
4. Desiree, nice big spuds but heavily scabbed, not good as chips (trying as mash next) I thought these were supposed to be quite scab resistant?
5. Maris Pipe - untested so far - still in the ground.

Having looked on the internet I think the potatoes have 'common scab'.

The soil is quite sandy did this add to the scab problem?

I tried to keep them well watered but it has been a hot dry summer, did this add to the scab problem?

Should I dig them up as soon as possible, will leaving them add to the scab problem?

Any tips for next year? I have read that alkaline soils doesn't help and adding manure makes the soil more alkaline, should I add manure to next years plot or is this bad information? What new varieties should I try?

I also noticed small yellow worms when digging them up - is this wire worm? One or two potatoes had holes in them but not very many at all.

Hi MickyB,
I too have noticed really bad scab on my second earlies (Red Duke of York), and I also have a light, sandy soil!  According to my googling, lighter soils make potatoes more prone to scab since they dry out more quickly, especially in the dry summer we've had.  I think variety also has a lot to do with it-my pink fir apples are untouched by scab, despite both kinds being grown in similar conditions.  This link has a few tips:

http://www.gardenersworld.com/blogs/allotments/potato-scab/2834.html

Ah well...they still taste lovely 

[sunshineband]

Pick out wireworm as you dig, to avoid them turning into click beetles and then laying more eggs.

As Trillium said, manure helps reduce alkalinity slightly, and lime increases it, so no lime for ground you are growing potatoes in next year, or the year following.

Some varieties are more resistant but peeling potatoes means you are not consuming it with skins. Scab shows up more on dry skins, so appears to worsen as they dry out imhe

[MickyB]

I have just done an internet search on 'wireworm' and I don't think they are the same as what I was seeing 
The bugs that I have been seeing are yellow, thin, about 1 to 1.5 inch long, loads of legs and wiggle like crazy when unearthed, maybe some kind of centipede? I will have to take a couple of snaps.

[Sparkyrog]

Scab got worse on my charlotte as the season progressed .

[MrsLev]

I think they are just centipedes, I don't think they cause any harm, when I've dug them up they always looked like they were just minding their own business under the ground.

[Salmo]

 Centipedes usually have about 20 pairs of legs and are very mobile. They are predators of many soil pests and therefore goodies to be encouraged..

[frizzy]

They sound like centipedes. Wireworm are shorter and thicker, from what I've seen.

[MickyB]

I am still not sure about the wireworm and started a new thread relating to this question here.....http://chat.allotment-garden.org/index.php?topic=109307.msg1233074#msg1233074

[MickyB]

The Maris Piper spuds look very badly affected by scab 

[mumofstig]

I've got very few that are good enough to cook in their skins or use as jacket spuds, this year