Is It Blight?

[BertieFox]

The 'mechanics' of blight. What is actually happening in its spread?

Lots of interesting stuff here, and we all accept that blight is a fungus that spreads from plant to plant via the spores landing on and infecting the leaves... or does it? And that it is worse in wet and damp conditions, and more likely to infect crowded plants?

I watched a You Tube video yesterday in which it was claimed that as blight spreads UP the plant, the infection starts near the bottom. Our observations would confirm this as lower leaves are affected first and then the top ones last, in tomatoes, though with potatoes it doesn't follow the same pattern.

How does the fungus arrive? Some say in the rain and wind from other infections, but why do people claim you should burn the plants so it doesn't remain in the soil? Why should we destroy the 'volunteers' from tubers left in the ground? Often these make healthy plants and how would the fungus spread from these growing plants to our new plantings, especially if they are many metres away? If the fungus is in the soil, why doesn't it infect ALL our plants of this family regardless of weather conditions?

And why aren't tomatoes growing in the greenhouse infected with blight by the soil when we have grown tomatoes in there year after year?

As I say, the actual mechanics of the spread of blight seem very strange to me and I have yet to see it adequately explained. If we understood it better we might be able to prevent it more easily.

[SarzWix]

There are two mechanisms here I think. Blight spreads usually from spores on the foliage which as you said are spread via rain and wind to land on other susceptible foliage. The thing with volunteer potatoes is that blight may have affected those tubers in the previous year and they would then be the beginning of the blight cycle in the current year. Of course it's possible to grow a decent crop from volunteer spuds, but unless they're a blight resistant variety, the risk tends to be higher of them starting the blight cycle. Blight can only survive in the soil in infected plant material, it only survives in the soil without a host for a couple of weeks, hence the advice to chop down affected foliage and leave the tubers in the ground for a few weeks before digging up, in the hope that any spores on the soil surface will die off before you bring the spuds to the surface.

[Mizjazzi]

Help please? Is this blight or do they need a feed?

I have brown edges on my second earlies (back right on the last pic.)and yellow leaves on the bottom of my main crop!?

Very high temperatures here for a whole week. OH JOY!!!
Some of the plants in my back garden have major leaf scorch!

However, the tatties ( mains) otherwise look healthy, and new growth is coming out where the yellowed leaves at the bottom are.
I earthed up, and that seems to be where the yellow leaves are.??

I am going to rempve all the yellow leaves anyway.
Actually I am also not sure that I do not need to earth up again?
I did fertilize before planting, should I do so again?

Thanks in advance, I usually did bags before but my yields were rubbish last year!

[Thelma Sanders]

It's very unlikely you will get blight while it is hot and dry weather. It thrives in warm and humid.

There is nothing in those photos that I'd be worried about

[Mizjazzi]

Thanks for that,

I have just picked off the yellow leaves and will keep an eye open.

Happy harvest

[esbo]

Lots of interesting stuff here, and we all accept that blight is a fungus that spreads from plant to plant via the spores landing on and infecting the leaves... or does it? And that it is worse in wet and damp conditions, and more likely to infect crowded plants?

I watched a You Tube video yesterday in which it was claimed that as blight spreads UP the plant, the infection starts near the bottom. Our observations would confirm this as lower leaves are affected first and then the top ones last, in tomatoes, though with potatoes it doesn't follow the same pattern.

How does the fungus arrive? Some say in the rain and wind from other infections, but why do people claim you should burn the plants so it doesn't remain in the soil? Why should we destroy the 'volunteers' from tubers left in the ground? Often these make healthy plants and how would the fungus spread from these growing plants to our new plantings, especially if they are many metres away? If the fungus is in the soil, why doesn't it infect ALL our plants of this family regardless of weather conditions?

And why aren't tomatoes growing in the greenhouse infected with blight by the soil when we have grown tomatoes in there year after year?

As I say, the actual mechanics of the spread of blight seem very strange to me and I have yet to see it adequately explained. If we understood it better we might be able to prevent it more easily.

Interesting post!!

I am no expect but have some theories based on common sense, one thing I thing is that maybe blight is there all the time but just needs the right conditions to thrive? Maybe the extra warmth of the greenhouse protects the tomato plants in there? After all they are not a native UK plant?
Same may go for the potato? But I am not sure about that?

Also I think over crowded condition may be an issue, I think it is the same with humans.

SO basically I think the virus is always there but need plants weakened by other things, cold or damp or over crowding or whatever, I think these weakened plants may not be able to fight off the virus but healthier one can because it can't get a foothold in them?

I would compare it to what we call a cold, apparently a cold is not caused by the cold but virus, but in my opinion it requires *both*.

So you get the scientists saying it is not caused by the cold, but the very name 'cold' is the big give away, cold weather is usually require *or* some other condition which weakens a persons immune system.

SO I would say the disease is only manifest in the plant when the disease can replicate itself faster than the plant can replicate anti-bodies (or what ever you might like to call it). Indeed it may actually be attacking that plant all the time but when the plant is strong enough to repel the attack all is well. If is 1 virus against 100 ant-bodies all is well, same goes if it is 99v100, but when it is 101v100 then the plant is a gonna!!

I suppose there is an analogy with AIDS, immune system deficiency, we come into contact with viruses all the time but that is not a problem for most people, the problem is when you get the combination of the virus *and* a weakened immune system. Same goes for plants I think, the blight virus is probably every present, of course if it is present in large number it is more of a threat as it requires a bigger immune response to fight it off.
That's my take on it anyway.

[esbo]

found this which kind of agrees with what i said
Mosaic virus, pictures of the yellow leaves on tomato plants

" Increasing the temperature in the greenhouse above 24°C (75°F) has been proven to reduce the effects of mosaic virus."

that is about mosaic virus but the principle is the same, when the plant is in ideal condition's it can cope better with disease.

unfortunately i have no green house and some of the leaves on my toms are looking
a bit unhealthy, shinier than normal and misshapen, and it seems to have spread a bit, I am chopping off the worst bits.
Hoping the tomatoes get growing and ripening faster than the disease or whatever.

[BertieFox]

Important to note that blight is not a virus but a fungus, though what you say could apply equally. Here with very hot conditions but plenty of humidity (heavy morning dew, several torrential thunderstorms) there is absolutely no sign of blight now on the tomatoes, though of course they dry out thoroughly in the heat of the day. I guess the fungal spores are there on the leaves and stems but cannot germinate due to the heat and drying out. I just hope this continues long enough to benefit from the huge harvest that looks likely this year, though I have counted my chickens before with disappointing results. Can't wait for all those yummy tomatoes though, and picked the first ripe one outside yesterday. Even greenhouse ones are quite late this year.

[Martin H]

Yesterday was the first day this year that our local weather conditions met the full Smith criteria. Looking at today's forecast, we might be about to hit our first Smith Period.

I'll be keeping an extra close watch on the potatoes and tomatoes for blight symptoms...

[WPG]

As the blightwatch map doesn't cover Northern Ireland, just wanted to let other N Irelanders know that the Dept of Agriculture NI have a blight map at

DARD Blight-Net 2013 | Department of Agriculture and Rural Development

There's been several risk periods, but only one actual warning in early July. So far, touchwood and fingers crossed, everyones' spuds look fine on my allotment in County Down (last year the blight had spread by mid July).

[BertieFox]

June 17th 2014

On Sunday I harvested some potatoes and the plants were in great shape. Then we had a heavy thundery rain storm with a northerly wind, and today I noticed a whole load of the potatoes with the characteristic brown blisters.

I blame blight being blown in on the wind and rain from the UK! But wherever it came from, it is such a disappointment as it means we have to remove all the potato foliage and harvest whatever the plants have made so far.

Worse, a few of the tomatoes have already been affected, and stupidly, I planted a row of them just next to the potatoes.

I shall spray the tomatoes tomorrow with Bouille Bordelaise as a preventative and hope that the sunny weather will keep the blight at bay there, but it means soiling the fruit with all that horrible blue copper stuff!

How do people elsewhere cope with blight? Is it a problem in your area? I am almost at the point of giving up on growing potatoes in future as this happens every year. Otherwise I will have to copy the French locally and spray everything with Bordeaux mixture early on.

[Marb67]

Do i have blight

Only the odd leaf but mostly healthy foliage. Destroyed the picked off ones just in case. Just hope it isnt blight.

All first early crops

[Rocketron]

June 17th 2014

On Sunday I harvested some potatoes and the plants were in great shape. Then we had a heavy thundery rain storm with a northerly wind, and today I noticed a whole load of the potatoes with the characteristic brown blisters.

I blame blight being blown in on the wind and rain from the UK! But wherever it came from, it is such a disappointment as it means we have to remove all the potato foliage and harvest whatever the plants have made so far.

Worse, a few of the tomatoes have already been affected, and stupidly, I planted a row of them just next to the potatoes.

I shall spray the tomatoes tomorrow with Bouille Bordelaise as a preventative and hope that the sunny weather will keep the blight at bay there, but it means soiling the fruit with all that horrible blue copper stuff!

How do people elsewhere cope with blight? Is it a problem in your area? I am almost at the point of giving up on growing potatoes in future as this happens every year. Otherwise I will have to copy the French locally and spray everything with Bordeaux mixture early on.

That's the only way I have found successful in East Sussex.

[Penellype]

Ive had blight on tomatoes, which ruins the crop completely - once it strikes you can guarantee that any green tomatoes will rot rather than turn red. I've not had much of a problem with potatoes, possibly because I grow them in bags. The foliage flops over so the blight spores (if any) probably fall onto the path rather than onto the soil and potatoes. I also leave the potatoes in the bags until I need them, removing the dying foliage and moving the bags into the garage. Apparently if you get blight it is better to cut off the foliage and leave the potatoes buried until you need them rather than hurrying to get them out of the ground. If you have earthed them up there is a chance the spores will be washed away down the slopes whereas if you dig them straight away the spores get onto the tubers. That's the theory - I have not tested it myself.

[Marb67]

Only the odd leaf but mostly healthy foliage. Destroyed the picked off ones just in case. Just hope it isnt blight.

All first early crops[ATTACH=CONFIG]46769[/ATTACH]

So is this blight ? I found some more leaves today i have pulled off. All in containers and not soil.