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Scab on Maincrop potatos
AJ203
Posts: 15
in Fruit & veg
I've just dug up all my Maincrop potatos. My First and Second Earlies cropped well and were clean skinned. In the same area of ground my Maincrop Cara and Desiree are universally covered in scab but the Sarpo Mira are clean. This is the first time I've grown potatos in this area of ground (it grew Brassicas last year), so is this a problem with the soil or was it weather conditions or bad seed potatos or something else???
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Scab is caused by bacteria i think and they thrive in soil with a high Ph. Did you add any lime?
I didn't lime the soil and I used a soil testing kit earlier in the year which gave the pH as 6.5.
If you limed the soil for the previous brassica crop traces will remain in the soil - hence scab. In my experience, Sarpo Mira shrug off just about everything, including blight.
Hi luckily todate my earlies Charlotte, Rocket have been perfect and my 2nd earlies Nadine are now being lifted and they are perfect.
However next doors garden at the allotment Stu is going mad because his main crop Desiree has scab but his Cara dont.
I remember from last year he had his brassicas in that bed and he limed the ground when planting them so he may need adjusting the soil with some good old fashioned manure
I dug one of my Desiree up yesterday and all is good so keeping my fingers crossed for them and the Cara and Picasso
Happy Gardening
Spuds benefit from lots of muck/compost, and this produces an acid environment. I always exaggerate this by lining or covering each drill with fresh grass cuttings. These produce acid as they rot and also provide extra nitrogen, which helps the potato foliage develop. If the soil is insufficiently acid, susceptible varieties will get scab. (and DIY pH tests tend to be unreliable in mu experience)
As far as rotation is concerned, I reckon it's a good idea to follow spuds with onions which will benefit from the left over organic matter but don't want it too rich. Then a little lime for beans; more the next year for brassicas (if you must - I don't like them much); muck for squashes, roots, then more muck for spuds again.
Hope this helps
If the Ph is 6.5 you shouldn't have much if any scab. When using a soil tes make sure the water used is clean and Ph Neutral. Rain water collected in a plastic bucket is fine. Tap water is not good as the council put too many chemicals in it. We have our own supply but it has too much lime so all tests are Alkeline.
Councils in the UK do not have any responsibility for water supply so can't put any chemicals in it. In England and Wales private companies are responsible, Scottish Water is a publically owned company answerable to the Scottish Parliament.
It should be possible to see details of your water supply quality on your water supplier's website which will give you a detailed chemical analysis of your tap water. This is governed by EU legislation and enforced by the Drinking Water Inspectorate in England and Wales.
Interesting comments about water supply but I'm on spring water which comes off Dartmoor so I'm not sure how this would affect a pH test!
hi all just dug up another three rows of nadine and they are perfect all bar a few see first tray-in picture. a few desiree also came from no where however i am very happy with the 2nd earlies Nadine one to plant again next year.
amazing size for jacket potatoes and they are very white excellent