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Is this potato blight?
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Topic: Is this potato blight? (Read 8837 times)
pieman
Not So New ...
Posts: 24
Is this potato blight?
«
on:
June 18, 2009, 16:18:41 »
Hi folks.
Noticed quite a few yellow leaves on my potatoes the other day, and saw the same on a few adjacent plots as well. This picture shows a leaf that doesn't seem as yellow as most of them, but I'm rather worried it's something nasty. Any ideas?
Thanks
David
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Tee Gee
Hectare
Posts: 6,930
Huddersfield - Light humus rich soil
Re: Is this potato blight?
«
Reply #1 on:
June 18, 2009, 17:20:52 »
Quote
doesn't seem as yellow as most of them,
The above statement suggests your potatoes are earlies that are dying back (yellowing) and if so this is not blight (in my opinion)
Am I correct in thinking they are earlies?
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The Gardeners Almanac
Kepouros
Hectare
Posts: 782
Re: Is this potato blight?
«
Reply #2 on:
June 18, 2009, 17:23:06 »
To be absolutely sure in diagnosing potato blight (either early or late) it is essential to see the underside of the leaf, and it would be helpful if you could show a photo of this (preferrably top and underside of the same leaf). However, even without this I`m pretty sure that what you have is not blight, but is probably a physiological disorder caused by either soil or weather conditions.
If you have a lot of really yellow leaves on your plants, with brown markings interspersed between the leaf veins, then you may well have a magnesium deficiency, although this could quite easily be a purely temporary one caused by either heavy rain or abnormally dry soil conditions rather than a general soil deficiency.
You will probably be advised by others to reach for the epsom salts immediately, and spray generously, but I would suggest that unless the plants are badly affected you wait a while, keeping an eye on the plants to see whether the problem gets worse or stabilises itself before doing so.
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davyw1
Hectare
Posts: 2,530
I love My Country
Re: Is this potato blight?
«
Reply #3 on:
June 18, 2009, 18:30:18 »
have a look at the photo on this link
http://www.allotments4all.co.uk/smf/index.php/topic,52605.0.html
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When you wake up on a morning say "good morning world" and be grateful
DAVY
pieman
Not So New ...
Posts: 24
Re: Is this potato blight?
«
Reply #4 on:
June 18, 2009, 20:15:21 »
Thanks everybody, those pics of a magnesium deficiency are exactly it.
As suggested, I'll leave using salts for a bit - made sure I watered them properly and will keep an eye on them.
This really is a very handy place. Thanks again.
David
PS: just noticed that apart from the link davyw1 gave me, shirlton's got a similar post with the same problem. Perhaps I'll look around the other topics a bit more next time!
«
Last Edit: June 18, 2009, 20:18:18 by pieman
»
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Unwashed
Hectare
Posts: 2,735
Vexatious, moi?
Re: Is this potato blight?
«
Reply #5 on:
June 19, 2009, 07:10:53 »
With magnesium deficiency the leaf dies between the veins, but that's not happening with your leaf.
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pieman
Not So New ...
Posts: 24
Re: Is this potato blight?
«
Reply #6 on:
June 19, 2009, 07:51:34 »
I see what you mean, but it's a bit hard to tell on that rather poor sample I used for the photo. I'll have another look today and perhaps post another picture.
D
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Unwashed
Hectare
Posts: 2,735
Vexatious, moi?
Re: Is this potato blight?
«
Reply #7 on:
June 19, 2009, 20:15:33 »
My guess is that it's blight - see those concentric rings in the brown bits - but I'm not sure.
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An Agreement of the People for a firm and present peace upon grounds of common right
Kepouros
Hectare
Posts: 782
Re: Is this potato blight?
«
Reply #8 on:
June 20, 2009, 13:16:01 »
I`m afraid that I have to disagree strongly with Unwashed on two grounds:-
1. According to the Potato Council Reports, the only cases of Blight so far are in Northern Ireland and South West Cornwall.
2. The markings on the leaf are not indicative of blight, but of drying necrosis, were they blight they would not appear dry and blistering, and with the extent of the patches the whole leaf would be severely chlorotic.
The leaf shows green veins with interveinal chlorosis, and severe interveinal necrosis - typical of magnesium deficiency.
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pieman
Not So New ...
Posts: 24
Re: Is this potato blight?
«
Reply #9 on:
June 22, 2009, 09:51:57 »
Thanks again everyone for your comments.
Hopefully these pics will make it clearer:
Top of Desiree leaf:
Underside of same leaf:
Bad case on the neighbouring plot:
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OllieC
Global Moderator
Hectare
Posts: 3,390
Nairn
Re: Is this potato blight?
«
Reply #10 on:
June 22, 2009, 09:55:26 »
They look the same as my swift & rocket every year...
There's a kit advertised in my magazine, claiming to tell you for sure if it's blight... about £6 from Harrods Horticulture. Not sure if it actually works though!
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Kepouros
Hectare
Posts: 782
Re: Is this potato blight?
«
Reply #11 on:
June 22, 2009, 18:18:19 »
I still think it`s not blight. If all those dark brown markings had been blight lesions most of the foliage would be dropping off by now. I`ll stick with magnesium deficiency
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Toadspawn
Acre
Posts: 456
Re: Is this potato blight?
«
Reply #12 on:
June 22, 2009, 23:07:07 »
I would agree that it is NOT potato late blight. It could be a nutrient deficiency/imbalance or just general dying off which is common in early varieties at this time of the year. Potato early blight caused by a completely different fungus shows similar symptoms but it is usually not worth trying to control it..
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