Topic: Potato Blight

[Monika]

My husband has just discovered that we have Potato Blight on our earlies - so he is now digging them all up.

This is not the first time he has had PB and is now wondering if it is now in the soil.

What is the procedure for dealing with this disease?

He rotates his crops on a three yearly rota to try to avoid such problems.

As I said, he is digging them up this morning to try to save some of them but, do you have to treat the soil after diging.

I'm grateful for any help on this matter.

[ceres]

Unlikely.  Read this thread and don't dig the potatoes up.

http://www.allotments4all.co.uk/smf/index.php/topic,53104.msg

[Kepouros]

If it is really Blight it certainly won`t have restricted itself to the earlies, and my guess is that if it really is Blight he`ll have it on the rest of his potatoes by this time tomorrow.  If he doesn`t, then 100 - 1 it wasn`t Blight

On the other hand,  I strongly suspect he`s panicking because he doesn`t know how Blight really manifests itself, and is mistaking the first signs of natural die back in the early foliage, or some simple physiological condition, for something much worse.

Either way there is no point whatever in digging up the potatoes immediately.  If there is no blight he is lifting the crop before he needs, and if there is blight he is actually exposing the tubers to risk of infection from fresh spores on the soil surface during the lifting.

Do as Ceres says, and follow the advice in the link she gives.

[OllieC]

Plenty of very experienced gardeners mistake natural die-back for blight... the easiest way to tell is after it's too late, when the spuds are putrid!

[Kepouros]

Shame on them.  They clearly haven`t learned very much from their experience - and one experience of blight is all that should be necessary to learn from.  There is virtually no similarity between the respective early manifestations of die back and blight when one has the actual plant (rather than a photograph) in front of one, and even where there is confusion on the first day of infection, there should be none by the second - which still leaves time to take necessary action.

[OllieC]

Go on then, what's the secret? Because some of them are on here... And I've had more than one experience of blight & haven't learnt so I must be a bit thick too!

[Kepouros]

There isn`t any secret at all, other than using one`s eyesight and memory, and any gardener who has anually seen his potatoes die back naturally (and ought to know very well what this looks like), and has also experienced confirmed Blight more than once (and has therefore had every opportunity to observe very well what this also looks like), and still hasn`t bothered to take careful note of the differences in symptoms must be either singularly unobservant or very unenquiring.

Natural die back in potato foliage normally starts with slight chlorosis of the leaf, which gradually deepens over a period of days and spreads over the whole leaf.  As it does so small irregular brown(ish) patches of necrosis may appear between the veins, or at the margins, and gradually spread, sometimes forming holes in the leaf as the necrotic tissue crumbles, until eventually the leaf either falls, or withers on the stem.

Blight, on the other hand, does not start with any preliminary chlorosis, but with a comparatively regular spot (which may be described as purplish/black, purplish/brown, blackish/brown - depending on your colour sensitivity) which appears (generally overnight) on the upper surface of a perfectly healthy leaf, indicating where a blight spore has lodged.  This mark is not necrotic and bears no similarity with the interveinal necrosis appearing in natural dieback. The colour staining does not at this stage extend through to the underside of the leaf, although it is visible through the leaf from the underside, and instead there is on the underside, and co-incident with it, a patch or halo of fine, whitish, furry looking fungus. These marks may appear at any point on the leaf, but more frequently near the tip or margins where rain or dew take longer to dry off. Once this spot has appeared the staining will slowly spread outwards, and as it does so a degree of chlorosis will probably also develop around it and spread through the leaf.  With stems, the spores  are most likely to lodge at a leaf axyl, again where moisture is more likely to have collected, or where the spore can more easily lodge, but occasionally on other parts of the stem, where they are categorised by a brown streak forming on the surface.

If blight appears on a healthy green leaf, particularly if more than one plant is affected, there can be no mistaking it for what it is.  Only if it appears on a leaf that is already dying or affected by some other ailment should there be any real confusion, but another 24 hours should resolve this as the blight spreads to other healthy foliage and uncontradictable symptoms appear.

[Bjerreby]

It can't be explained in more plain terms than that Kepouros. Thanks.

[OllieC]

Oh dear, I must be even more stupid than I thought, thanks for trying but this really doesn't clear it up for me at all.

[Hector]

Kepouros,
thanks for interesting info. Does same principals apply with Tomato blight? ie/not starting as a gradual chlorosis?

[Baccy Man]

Natural die back in potato foliage normally starts with slight chlorosis of the leaf, which gradually deepens over a period of days and spreads over the whole leaf.  As it does so small irregular brown(ish) patches of necrosis may appear between the veins, or at the margins, and gradually spread, sometimes forming holes in the leaf as the necrotic tissue crumbles, until eventually the leaf either falls, or withers on the stem.

Blight, on the other hand, does not start with any preliminary chlorosis, but with a comparatively regular spot (which may be described as purplish/black, purplish/brown, blackish/brown - depending on your colour sensitivity) which appears (generally overnight) on the upper surface of a perfectly healthy leaf, indicating where a blight spore has lodged.  This mark is not necrotic and bears no similarity with the interveinal necrosis appearing in natural dieback......

What you have said is true for late blight caused by Phytophthora Infestans however early blight caused by Alternaria Solani usually first becomes evident in senescent leaves, causing dark necrotic lesions in a characteristic concentric pattern. Both early & late blight are problems within the UK. Initial symptoms of early blight can be mistaken for natural dieback, if no action is taken then the disease spreads rapidly.

[Tattieman]

Monika can you put a picture on here of the suspect plants?

[Kepouros]

Baccy Man is quite correct.  My posting was entirely in respect of Phytophthera Infestans.  This was for 2 reasons:-
1. I thought the thread was intended to be about Late Blight
2. I saw no reason to confuse the issue by also discussing a disease that in fact does very little damage in the UK other than to foliage.  I don`t think it has ever been a matter of serious concern, and in fact the Potato Council has no advice to offer and considers it to be an economic irrelevance.

If Baccy Man were to be gardening in the USA or Africa I could understand his concern, since in those areas the effects of ignoring the disease are very much as he describes.  However, as I understand this not to be the case his fears are virtually  groundless.

To Hector, yes, the Blight infection starts in exactly the same way on tomatoes provide it starts on a healthy leaf.  But it obviously can, of course, start in a leaf that is already chlorotic for other reasons

[Bjerreby]

Again, it can't be explained in more plain terms than that Kepouros. Thanks.   :)

[OllieC]

Again, it can't be explained in more plain terms than that Kepouros. Thanks.   :)

Are you guys lovers or something?

[Baccy Man]

2. I saw no reason to confuse the issue by also discussing a disease that in fact does very little damage in the UK other than to foliage.  I don`t think it has ever been a matter of serious concern, and in fact the Potato Council has no advice to offer and considers it to be an economic irrelevance.

If Baccy Man were to be gardening in the USA or Africa I could understand his concern, since in those areas the effects of ignoring the disease are very much as he describes.  However, as I understand this not to be the case his fears are virtually  groundless.

If you had previously had previously had around 3 acres of potatoes, tomatoes & peppers infected with early blight you may view the matter differently. Admittedly it has only been a significant problem on one occasion in the last 9 years however I don't believe any concerns I have regarding this disease are groundless.

[amphibian]

Again, it can't be explained in more plain terms than that Kepouros. Thanks.   :)

Are you guys lovers or something?

Well if they are, I must be part of their love in, the explanations were detailed, helpful and accurate and deserve acknowledgment. Kepouros has provided this information many times over, in many threads and it is valuable information for any grower of potatoes or tomatoes. We are all wont to panic about blight and take rash actions to remedy a problem we often don't have, at huge detriment to our crop and our pockets. Attempts to educate us away from this folly, should be commended.

[OllieC]

I wasn't arguing about the advice, although I did find the earlier tone a bit patronising & also oversimplified... I know it was well meant. You can't say "shame on anyone who can't tell the difference" and then demonstrate that it is indeed more complicated than you originally said, without getting a slight ribbing! Just find it funny, that's all!

One person who sprang to mind was a chap I was talking to last week. He's 62 and has been a biologist all his life (and also a keen gardener), and it was him who told me he can't always tell the difference. So, shame on him, apparently!

[Bjerreby]

I wasn't arguing about the advice, although I did find the earlier tone a bit patronising & also oversimplified... I know it was well meant. You can't say "shame on anyone who can't tell the difference" and then demonstrate that it is indeed more complicated than you originally said, without getting a slight ribbing! Just find it funny, that's all!

One person who sprang to mind was a chap I was talking to last week. He's 62 and has been a biologist all his life (and also a keen gardener), and it was him who told me he can't always tell the difference. So, shame on him, apparently!

I wasn't going to write this OllieC, but now you replied as you did, I can't hold back.

Most people under 60 these days have learned to use computers. That learning was most likely a trial-and-error method, and they put it on their CV like some kind of qualification. The computer age has, in my view, intensified an  already insufferable arrogance among the human race.

Kepouros on the other hand, reminds me of the people who TAUGHT me the unchangeable basics of my business, which forms a solid foundation for what I have done for many years.

We might think we can manipulate plants, and to a certain degree, we might. But there comes a time when we pompous Homo sapiens must bow to nature. And I believe from Kepouros' postings, he is very clear when we must bow. Does that make him  patronising? Should we charge you with being arrogant? I think not. Kepouros is wise in my view, and I excuse his irritation at our folly. For your part, I am sure you are reasonable and will reflect on the wider issue.

[Tattieman]

Early blight or late blight you still want to control it as it will damage your overall crop. If I saw I had blight I would remove the leaves in question and dispose of them. There are plenty of images on google that you can use as a reference point.