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Scab on Seed Potatoes does not pass to Soil or New Tubers – An Experiment

Scab on Seed Potatoes is not a problem
The vast majority of our tubers will arrive with our customers in perfect condition

We specialise in rare and Heritage varieties and in some cases scab may be present.  We address this issue publicly.

Scab is legally permitted in seed potatoes in the UK, as it does not pass to the following generation

Scab does not pass to the next generation

Scab on Seed Potatoes is the elephant in the room.  The expectation that a seed potato will be 100% perfect is not what reality is, although this expectation will be met 75% of the time. 

Seed Potatoes are not as visually appealing as potatoes you buy to eat.  They will be dirty and may have small amounts of scab and mechanical damage that are within permitted levels for seed potatoes.   THIS IS ESPECIALLY TRUE IF YOU BUY ORGANIC OR HERITAGE VARIETIES.  If a crop passes inspection it does not mean that it is blemish / scab free, however the potatoes are still in perfect condition to grow.  We specialise in rare and Heritage varieties and in some cases scab may be present.  We address this issue publicly.

Which? and the Royal Horticultural Society, as well as all of the major TV presenters and magazines agree that Scab does not pass on to the soil or the new generation of potatoes.  This is backed by science.

We know that getting some potatoes that have scab can be a disappointment, especially if other potaotes in your order are perfect.  Scab affects different varieties on different years to varying degrees.

Common Scab at low levels is principally a cosmetic issue and does not affect the ability of the seed to produce a good crop. For this reason, the UK and EU tolerances permit the tubers to have up to 33.3% of surface area affected with common scab.

All of our seed is cerfitied which means the harvest has been tested and passed inspection. On occassion we cannot sell a variety due to scab or other reasons. 

However all this technical mumble-jumble is lost when a customer is not happy with the quality of their seed potaotes. We at Potato House completely understand the disappointment - imagine going to get your family some ice-creams and one flavour isn't frozen enough, to be told that is actually within the legal limits.

We want to help with the understanding of scab and so have this experiment going.

“Don’t worry if some of the seed potatoes you buy have a bit of scab on them. Scab is legally permitted in seed potatoes in the UK, as it does not pass to the following generation.”

Which? Gardening Helpdesk

6 Tubers chitted on 6/4/23

Scab on Seed Potatoes.
Our experiment to show that Scab does not pass to the next generation.

It is unsightly, but safe to plant.

Scab on Seed Potatoes is not a problem

Scab on Seed Potatoes - Day 1. 6th April. Chitting in an egg box

A customer returned these potatoes to us as they were not happy with the quality.

Although they had been out of cold storage and in transit for a few weeks, they were in perfect condition and beginning to sprout. 

At the start of the Easter Holidays they were officially put in an egg bog.

Scab in Seed Potatoes is dsafe to plant
Seed Potatoes with scab are fine to plant

Scab on Seed Potatoes Day 11. 17th April. Healthy Chits

By day 11, healthy shoots are appearing on all tubers. 

We are just north of Dundee and April is the usual time for us to be chitting, so this experiment fits in well with our growing schedule.  Although we have grow all the potatoes we can have commercially, we do like a few on the patio.

Chits/ shoots should be small and dark in colour. Long spindly shoots have been chitted in the dark, and are searching for the light. 

Scabby potaotes produce healthy shoots
healthy shoots from scab seed potatoes

“Legislation controls the amount of infection allowed in seed, but low levels are permitted”

Royal Horticultural Society

So far, so good.

Check back soon for our planting session when we will be planting our scabby seed potatoes. 

It is minus temperatures overnight just now with us, so it will be the start of May.

This experiment  is limited.  If the new tubers do get scab, it really is down to environmental factors, but I know that will not help if you believe that the seed potatoes are to blame.  The only control would be to plant the same variety which does not have scab, however this variety comes from the same field, and so all tubers are affected the same.

If the next generation of potatoes get scab, this is an unfortunate coincidence, not hereitary.  If I break my leg then my daughter does, it doesn't run in the family. 

Planting mid July - a bit later than planned

We had meant to plant these in May, but to be honest, they were left in the shed and forgotten about.  The video shows them being planted out in mid July and so has turned into a double experiment about Christmas Potatoes as well as potatoes with scab.

There were some lovely healthy shoots on all of the tubers.  If the shoots are long and spindly they have been searching for the light.

 

We abide by the rules set in The Seed Potatoes (Scotland) Regulations 2015.

If scab-free potatoes is the goal, we do have varieties that are scab resistant

All disease tests and scores are done by independant trials over many seasons. We have the results for all of these including Scab and Blight on a tab on each variety.  When we say scab-resistant we really mean it!  The scab-resistant varieties tend to be potatoes which have been bred recently for this characteristic. 

Note the word resistant. In severe cases these varieties may get scab and you need to ensure contstant watering during tuber formation to reduce the liklihood of scab.

See our post "Scab At Harvest" for more details.

4 thoughts on “Scab on Seed Potatoes does not pass to Soil or New Tubers – An Experiment

  1. John Tait says:

    following your RHS Link I read “Select seed carefully and avoid planting seed potatoes that have visible signs of scab”

    1. Amy Skea says:

      You are absolutely correct. If you read the very next sentence you will find “Legislation controls the amount of infection allowed in seed, but low levels are permitted”

      The levels are determined by industry experts and we follow the rules and recommendations set in The Seed Potatoes (Scotland) Regulations 2015.

  2. John Tait says:

    I ordered from you once
    The seed potatoes had considerable amounts of scab I have not bought from you again
    You might want to factor that in to your growing experiment
    Elsewhere you will read “Common scab of potatoes is a soil-borne disease caused by the bacteria-like organism Streptomyces scabies”
    Our own soil is prone to scab so we grow in large potato pots the compost cost is considerable and if it becomes contaminated by scab from seed potatoes then that seems like an self inflicted problem
    I buy seed potatoes now from a garden centre not from online suppliers like yourself largely because I want to see what I am getting
    I hope your experiment proves your point that seed potatoes with scab will not transmit the disease to the soil but it seems to go against conventional wisdom and indicates that you intend to continue supplying seed with scab
    So although I wish you well I suspect you might be better to try growing on less infected land or sell your potatoes mainly for eating
    Good luck for the future

    1. Amy Skea says:

      It is great that you are still growing potatoes – and we love that you are supporting your garden centre. Garden centres will generally only have the mainstream varieties whereas we specialise in rare and heritage varieties. At Potato House we are committed to keeping as many heritage and speciality potato varieties alive and available to gardeners and allotment growers. Many of these rare varieties are grown only on a small scale in one field on our own farm or by another farmer.

      If we only supplied seed stocks of the heritage and speciality varieties that are 100% visually perfect, we would need to dispose of a high percentage of our harvest every year, prices would rocket and then it would no longer be viable to supply many of these varieties since they are grown solely for the garden market. We could just grow the crops with little risk of scab but then these rare varieties could be lost. It’s not what Potato House is about!

      Please can you show me a quote from a reliable source to show your point that this goes against conventional wisdom. All gardening programmes give the same advice. We quote from two very well respected sources in the gardening world, and we use these quotes with permission.

      Our harvests are inspected (as are harvests from all growers) and a crop will either pass of fail, there are no degrees of passing. We do occasionally have crops that fail due to too much scab or other reasons. If a crop passes inspection we shall certainly intend to supply it and will continue to educate our customers about scab on seed potatoes. If you have issues with the amounts allowed on seed potatoes, perhaps you should try to change the legislation, rather than complaining that companies abide by it. The legislation comes about from many years of research by industry experts and can be found here The Seed Potatoes (Scotland) Regulations 2015.

      We have a 8-12 year cycle for our crops and so your suggestion to grow on less infected land is interesting – what do you propose we do?

      We are a Seed Potato company, but your suggestion about eating potatoes is great and one that we have already implemented. We had always sold some Potatoes to Eat to box schemes and locals. Last year we introduced this on our web – have you tried any yet? Perhaps this year you can try some heritage varieties to eat.

      Interestingly, you do not mention if your harvest had scab, just the seed potatoes.

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