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Common potato Scab, Management of the problem.

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James Kilkelly
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Joined: 30 May 2006
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PostPosted: Fri Mar 21, 2008 2:40 am    Post subject: Common potato Scab, Management of the problem. Reply with quote

Common potato Scab, Management of the problem.

It amuses me sometimes how certain words that cropped up regularly during my national school education, continue to haunt me long outside the educational system. Take for example the word "scab".

At break time in the schoolyard, the word usually came up when I asked a schoolmate for a handful of his Tayto crisps, the usual response was to be told, "You're such a scab". Fast forward to the summer of 2006, and that same school mate who berated me for scabbing a few crisps, is now asking my opinion on how to cope with scab on his home-grown potatoes. Scabs and potatoes seemed to have forged a link between the two of us, so, what could I do but offer him my advice.

Common potato Scab
Common potato Scab appears as raised rough sections on the skin of the potato, giving it a scabby or ruptured warty effect. It is usually the outer edge of each scab which is raised, with the centre slightly depressesed, much like the gardener who discovers this disease amongst his crop. The scabs are roughly circular and are rarely more than a centimetre wide apiece, although they can unite in one body or mass over time.

Thankfully common scab is little more than visual annoyance, meaning that at the end of the day, potatoes affected with the disease should be served up as mash rather than in their jackets, so as to be more pleasing to the eye. The potatoes are perfectly edible once you peel away the scab afflicted skin and its associated shallow flesh discolouration.

The disease which causes your scab is know as Streptomyces scabies, an infectious form of life somewhere between a bacteria and a fungus. This occurs naturally in most soils, but is especially present in high lime content sandy soils, which have recently changed from grass.

The distinctive raised rough sections on a scab infected potato, photo / picture / image.

Common potato Scab scientific classification
Kingdom: Bacteria
Phylum: Actinobacteria
Class: Actinobacteridae
Order: Actinomycetales
Superfamily: Streptomycineae
Family: Streptomycetaceae
Species/Genera: Streptomyces scabies

Management of the problem.

Arrow 1. You should avoid planting potatoes in areas directly after grass, especially grass that contained clover within its seed mix. Also, avoid sowing potatoes into areas that recently grew members of the brassica family, such as cabbage, cauliflower, brussel sprouts, broccoli, radish, swedes and turnips. Leave a year or two between grassland/brassicas and your potatoes, instead plant garlic, shallots, scallions and leeks, followed by carrot, parsnip, beetroot, parsley and celery.

Arrow 2. Don't add lime to ground where your potatoes are to be grown, as retaining an acid PH of 4.5 - 6.0 is helpful in the control of scab. Check your soils PH with a home test kit if you are unsure.

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To this end, avoid alkaline organic fertilisers such as ashes, poultry/fresh farmyard manure, and if applying artificial fertilisers ensure they are the acid producing kind such as sulphates. One traditional way to increase the acid levels in the immediate soil area around your potato crop is to add handfuls of wilted comfrey or grass clippings to your planting trenches just before the potatoes go in.

Arrow 3. Only plant certified seed potatoes displaying no visible signs of scab on planting day. You will further limit the possibility of scab occurring if you plant one of the varieties rated as scab resistant, there are quite a few, for example......
King Edward,
Arran Comet,
Arran Pilot,
Golden wonder,
Lady Balfour,
Maris Peer,
Pentland Crown,
Juliette, Accent,

Avoid susceptible varieties such as Desiree, Foremost, Majestic, and Maris Piper.

If you are looking for seed potatoes you may be able to source some here....Seed potatoes

Arrow 4. Finally, Avoid letting the soil around the growing potatoes dry out, this not only promotes the development of the disease, but can also lead to cracking of the scabs. Be especially careful of this if you are growing your potatoes in containers such as bags or stacked tyres.

Associated content.....
Grow your own potatoes.

Increasing your stock of seed pototoes, How-to Video.

How to chit seed potatoes for earlier and heavier cropping.

How to grow new potatoes for Christmas.

How to manage the top two potato pests, Wireworm and Slugs.

Planning a Vegetable Garden? How to Make a Vegetable Garden.

Any queries or comments on common potato scab, please post below.

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