Allotments 4 All
Produce => Edible Plants => Topic started by: Silverleaf on July 08, 2014, 13:24:44
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How do you tell the difference between blight and the normal dying-off process?
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I thought this should have it's own thread as there already seems so much L. Blight around.
I find potato haulms dying back naturally is gradual, with a slight yellowing browning of leaves and the stems quite often just sort of flop. Underneath you will have a good crop of mature potatoes at it's really an end of life cycle. L.Blight on the other hand can hit at any point (with the right conditions) and wipe out rows of previously very healthy green tomatoes in a short space of time. Blight is often first recognisable as dark or brown patch on a leaf, if you turn it over there is a sort of white area corresponding to the above patch. Stems are also affected, sometimes you get dry looking patches on the leaves but if wet weather continues the plant goes to a smelly mush even more rapidly.
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Thank you! I was wondering since I've never seen blight before. My Estima potato hauls are getting lighter in colour and look a bit floppy, and I found a yellowing leaf with a couple of dry brown patches on the edges. Didn't know whether to worry or not! Desiree and Charlotte either side of the Estima look dark green and healthy.
I guess blight's much easier to recognise if you have experience of it...
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First picture is my potato patch last year just as Late Blight struck,
The next two are blighted leaves I spotted that day
The last picture is 2 weeks later, the white flowering variety is one of the few survivors.
Normally I'd cut down the haulms as soon as seen, but last year I left them. I lost some spuds in the ground but surprisingly not that many, except for a few which had quite high losses including Pink Fir Apple.
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First two pictures are Sarpo Axona showing some signs of blight infection, but they grew through it and were able to shrug it off without too much harm.
Third picture is of two surviving varieties amongst those that weren't!
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If it helps someone some more photos of blighted leaves
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That's very helpful, thank you!
I think mine are fine, but I'll take some pics tomorrow and post them.
It's been a few years since I've grown potatoes and my poor old fibro brain doesn't remember very well... ;)
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When the blight hits the leaves rapidly go brown and the stems also tend to be hit quickly. When they die off, the stems may start to dry a little and take a woody texture but they don't look rotten. When they die off, the leaves go yellow, usually from the bottom up and these yellow leaves may get brown spots which is what I think causes confusion. The plants also tend to start to keel over a little.
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This is normal then, right?
(https://farm4.staticflickr.com/3912/14426040027_694572f868.jpg)
(https://farm4.staticflickr.com/3915/14425822468_f7b02fb92a.jpg)
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To me at least, that is how they look when they are dying off, yes.
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I think i might be seeing the start of blight now - the Charlotte and Estima leaves are yellowing and the plants flopping over, and I'm seeing some bigger patches of brown rather than just dry brown around the edges. And there are a few small brown patches on the otherwise not-dying-off-yet Desirees.
Think I'll cut off all the bits that have brown on them later today. I don't have many plants so I don't want to risk losing the crop! It's so hard to know if I'm panicking over perfectly healthy potatoes though, since I'm really not experienced with blight. :/
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What do you think?
(https://farm4.staticflickr.com/3863/14746696412_fdd361cd5b.jpg)
(https://farm6.staticflickr.com/5587/14746697112_16c2aa3e63.jpg)
(https://farm4.staticflickr.com/3889/14743819451_7bc9578d85.jpg)
(https://farm6.staticflickr.com/5572/14743820061_a11fbcbe8a.jpg)
(https://farm4.staticflickr.com/3856/14560532427_c8e7909235.jpg)
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Yellowing and flopping over don't really sound like Late Blight, which when it strikes takes hold at an incredibly fast rate, what you see as a small little mark one day will be a great big brown splodge the next.
Brown spots and patches sound like they could be part of the dying back process if yours are ready, but as you also have some brown patches on your Desirees it might be signs of Early Blight (Alternaria Species) or perhaps a mineral deficiency?
I've noticed some brown marks on my potatoes leaves which I think is Early Blight, I'll probably pick off a some leaves, but otherwise not much to do unless you want to spray with Dithane 945 Replacement.
I wrote the above and went for a cuppa, then saw your pictures. Top one looks like it is generally yellowing is it Charlotte?
Bottom two pictures look the iffiest although again some yellowing. Like you suggested take of the affected leaves. Any marks on the stems?
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Link for Early Blight info http://www.potato.org.uk/sites/default/files/%5Bcurrent-page%3Aarg%3A%3F%5D/Managing%20the%20risk%20of%20Early%20Blight%20-%20Alternaria%20Species.pdf
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I've forgotten which is which, but I think the top one is Charlotte, the next two are Desiree (darker leaves than the other two, and I can see a bit of anthocyanin in the foliage there) and the bottom two are Estima.
I can't see any affected stems...
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I cut off most of the brown bits this afternoon, and all of them are crispy and dry. Blight's mushy, right?
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I cut off most of the brown bits this afternoon, and all of them are crispy and dry. Blight's mushy, right?
Not quite. At the stage where there are just a few blackish blight spots on the leaves, it can happen that we get a few days of dry weather with low moisture in the atmosphere. This will crisp up the spots and stop further spreading - for a while! Most of the time the weather does not cooperate and then blight spreads at a dramatic rate. Once it goes to the stems in addition to the leaves, it is usually doom time! But leaf blight may not develop further (and I think yours in the photos have done just that - the dead blighted plant tissue crisps up.)
Looking at your last 2 photos, I would say these are blight spots.
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Thanks! I haven't seen any more brown bits since I removed the suspicious leaves, apart from a couple in the middle of yellow leaves.
I'll keep an eye on it and keep cutting off brown bits.
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I've seen that there is some evidence of early blight around our allotments now and some causing pretty severe dieback. Given that late blight will probably be along in a short while as well, I took the decision to cut down the manky looking haulms on my main crop desirée potatoes about 10 days ago.
I'm so glad I did - the harvest today has been spectacular ... the potatoes are so large, plentiful, and clean that I can't believe that leaving them in the ground until late August could possible have improved them. There were very few of the usual tiny potatoes that grow and I now have 3 big sacks of impressive pink potatoes.
:icon_cheers:
I'm not saying it will be the same in every area - but it might be a good idea to dig up a test plant of your main crop to see if there's a decent harvest already there - and then you won't have to worry about blight, slugs etc.
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That's not a bad idea, although my potatoes went in late this year so they may not be as big as they could be.
I might have an experimental poke around and see what they're doing down there.
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It isn't always easy to tell what's the problem more so in the early stages coupled with possible dual problems. Hope you tatties make it through :happy7:
Here's a couple of mine with I think Early Blight
I did read somewhere that if you take a leaf you suspect to have Late Blight (before it is obvious or weather is very dry to mask early symptoms) and put it on damp kitchen paper inside a bag and leave it for 24hrs, white fungal growth should be apparent on the underside of the leaf if Late Blight.