Potato Blight

Alanstrainor

Hey guys, so this year is my first year growing veg of any kind. We have a large bed with about 20 seeder potatoes planted back in March. They've been growing really well, and are now just flowering. I just came back from a weeks holidays and noticed that some the leaves have spots and some are yellow. From my research it looks like blight.

As a first step I have removed the leaves the were affected. For the most part the plants look okay but I am wondering what my next steps should be. I've read that once blight sets in you should cut the plants back completely and leave whatever spuds have grown in the ground for a couple of weeks to harvest.

My thread really boils down to the question, do i:

a) Leave the plants as they are, with the spotted leaves removed and keep and eye on them moving forward.
b) Cut them back completely.

Keeping in mind that this has only set in, in the last week or so.

Cheers!

macraignil

Alanstrainor wrote: »

Hey guys, so this year is my first year growing veg of any kind. We have a large bed with about 20 seeder potatoes planted back in March. They've been growing really well, and are now just flowering. I just came back from a weeks holidays and noticed that some the leaves have spots and some are yellow. From my research it looks like blight.

As a first step I have removed the leaves the were affected. For the most part the plants look okay but I am wondering what my next steps should be. I've read that once blight sets in you should cut the plants back completely and leave whatever spuds have grown in the ground for a couple of weeks to harvest.

My thread really boils down to the question, do i:

a) Leave the plants as they are, with the spotted leaves removed and keep and eye on them moving forward.
b) Cut them back completely.

Keeping in mind that this has only set in, in the last week or so.

Cheers!

I would reckon it would depend on what variety of potatoes you are after growing. If they are an early variety you could already have a reasonable crop ready to harvest. If they are main crop potatoes there may be very little to harvest yet and there would be little point trying to harvest straight away. If you're unsure which they are I'd try digging one plant worth of spuds up now just to see what's after growing.

It's a good time now to "earth up" around potatoes as this will give a better crop and offer some protection from blight going into the potatoes in the ground. This simply involves pilling earth onto the potato plants leaving only the tops showing. This should not kill the plants which are vigorous enough to keep growing and will also stop new potatoes near the surface going green.

Alanstrainor

macraignil wrote: »

I would reckon it would depend on what variety of potatoes you are after growing. If they are an early variety you could already have a reasonable crop ready to harvest. If they are main crop potatoes there may be very little to harvest yet and there would be little point trying to harvest straight away. If you're unsure which they are I'd try digging one plant worth of spuds up now just to see what's after growing.

It's a good time now to "earth up" around potatoes as this will give a better crop and offer some protection from blight going into the potatoes in the ground. This simply involves pilling earth onto the potato plants leaving only the tops showing. This should not kill the plants which are vigorous enough to keep growing and will also stop new potatoes near the surface going green.

Thanks for the tips. They are main crop kerr pinks, grown from seed potatoes planted in March. We did earth up once when the plants reached maybe 1ft in height which spurred on the growth massively. They are over twice as high now and have just flowered. If you think a second earthing up will help then that's what we'll do. I'll post up pictures of what I have this evening, I wish I had photographed them before removing the affected leaves but oh well.

cuculainn

Hi,


first time growing spuds here too,
Do most people spray to prevent blight?
if so what do people spray, i am trying to stay organic so dont want to be doing too much spraying.



I have heard of copper sulphate being used?

gozunda

cuculainn wrote: »

Hi,


first time growing spuds here too,
Do most people spray to prevent blight?
if so what do people spray, i am trying to stay organic so dont want to be doing too much spraying.



I have heard of copper sulphate being used?

There have been blight warnings already issued about 2 weeks ago by Met Eireann. Always try and spray spuds at time of warning before rainfall etc with something like Bordeaux mixture which is a premix of copper sulphate and slaked lime.

I've came across a few sites that have instructions on how to do this on line.

Best of luck ...

Alanstrainor

So here's what I have. Keep in mind that I had already removed leaves yesterday before I had really thought about it.

Alanstrainor

So I dug up one plant today and found some decent spuds. So decided to cut back all the plants and hope for the best. The blight was pretty unstoppable across all plants so hopefully nothing has made its way into the spuds.

I'll dig up what's there in 2 weeks.

DBB

Have you cut the plants right back to the ground?
Kerr's Pinks are very prone to blight, although your photos don't make them look blighty to me, though you do say you'd picked off affected leaves so maybe it's hard to tell.
If you have cut the foliage right back to the ground, and it is blight, then I'd question the wisdom of leaving the spuds in the ground... Without foliage there'll be no more growth, and I'd fear you're leaving the spuds more vulnerable to blight by leaving them in the ground. If the plants were in flower, it's damn close to harvest time anyway!
For future reference, spray at the first sign of blight. Also, as already advised, spray as soon as blight warnings are issued. If blighty foliage appears, pull the affected leaves off and burn them. I'm kinda befuddled as to why one should cut all foliage away and leave the spuds put, to be honest... Unless I've picked you up wrong!

Zzippy

DBB wrote: »

Have you cut the plants right back to the ground?
Kerr's Pinks are very prone to blight, although your photos don't make them look blighty to me, though you do say you'd picked off affected leaves so maybe it's hard to tell.
If you have cut the foliage right back to the ground, and it is blight, then I'd question the wisdom of leaving the spuds in the ground... Without foliage there'll be no more growth, and I'd fear you're leaving the spuds more vulnerable to blight by leaving them in the ground. If the plants were in flower, it's damn close to harvest time anyway!
For future reference, spray at the first sign of blight. Also, as already advised, spray as soon as blight warnings are issued. If blighty foliage appears, pull the affected leaves off and burn them. I'm kinda befuddled as to why one should cut all foliage away and leave the spuds put, to be honest... Unless I've picked you up wrong!

AFAIK they are left in the ground for the skin to toughen up, if dug straight away the skin will be paper thin. Once the plants are cut back there is very little risk of blight getting to the tubers.

Alanstrainor

Zzippy wrote: »

AFAIK they are left in the ground for the skin to toughen up, if dug straight away the skin will be paper thin. Once the plants are cut back there is very little risk of blight getting to the tubers.

Yes that was the logic. All my reading online suggests the same. The plants were cut back right to the ground, there's no foliage left at all.

As for the pics not showing too much blight, it was a case of it being a never ending slow battle. Every evening more leaves would have spots on them, with some going yellow and brown. I'd pick as many affected leaves as I could see and repeat the next day. I had earthed up again to protect whatever crop there was also.

Thanks again for the advice everyone, I'll post a picture of the harvest when they're out of the ground.

yogibear77

I've been following this thread as I planted a couple of baby potatoes in a large pot to see if they would grow....they did to my amazement. I think they got blight so the flower s have died off. I have just pulled them up and was amazed what I got.

My question is when can we eat them?

Zzippy

yogibear77 wrote: »

I've been following this thread as I planted a couple of baby potatoes in a large pot to see if they would grow....they did to my amazement. I think they got blight so the flower s have died off. I have just pulled them up and was amazed what I got.

My question is when can we eat them?

You can cook them as soon as you dig them if you want to.

gozunda

yogibear77 wrote: »

I've been following this thread as I planted a couple of baby potatoes in a large pot to see if they would grow....they did to my amazement. I think they got blight so the flower s have died off. I have just pulled them up and was amazed what I got.

My question is when can we eat them?

Get the pot on!

You can enjoy them straight away or if you wish to keep some - let them dry out for a couple of days. I use a dark shed for this and spread them out in a single layer. It's important to exclude light completely or you risk them turning green. Cover with something like jute sacking or paper.

Once the skins are fully dry and are hardened place the potatoes in bags (not plastic) and store someplace dark cool and dry

Enjoy

yogibear77

Thanks for that. I only planted 2 just to see what happened lol unfortunately we don't have any for storing.......We had them for dinner. They were delish.....My OH still can't believe they grew

amandstu

Has anyone else noticed blight this year?

I don't recall seeing any warnings yet on RTE and with the spell of fine dry weather promised over the next while I am starting to feel confident that I might get some spuds before the blight arrives in due course.

hawkwing

Could it be that they are too dry also?,i have similar yellow leaves on some pinks that were not watered,but i watered them today--will see what happens.Have sprayed twice already with copper mixture. Think the whole crop badly needs rain. Surely a blight warning should be out currently,humidity at 99% and drizzly...

amandstu

hawkwing wrote: »

Could it be that they are too dry also?,i have similar yellow leaves on some pinks that were not watered,but i watered them today--will see what happens.Have sprayed twice already with copper mixture. Think the whole crop badly needs rain. Surely a blight warning should be out currently,humidity at 99% and drizzly...

Fantastic rain today. Should keep them(and the rhubarb) happy for a while -although I expect to be back watering them after a few more days.

This dry weather is a bit out of character:D

gk5000

There needs to be two consecutive days of high humidity. The UK used "Smith Periods" which specified 2 days with at least 11 hours greater than 90% humidity - but this is now being replaced by Hutton Criteria which suggests only 6 hours.

In Ireland Met Eireann use some formula - called something like "Irish conditions" to issue blight warnings.

I doubt if there is any blight spread in the current dry conditions, nor anything significant in the previous photo.

There may be little spots on individual leaves, but I don't think that's a problem. If the conditions don't allow it to spread then those leaves will die and the plant will continue to grow. I read somewhere that the tubers are still growing if 25% of the foliage is still there. I personally would not be a big fan of cutting off all foliage unless it was already dying and the stalk wilting.

• A Smith Period is at least two consecutive days where min temperature is 10 °C (50 °F) or above and on each day at least 11 hours when the relative humidity is greater than 90%.

https://www.fginsight.com/news/news/smith-period-blight-alert-set-to-be-replaced-17368
"While the current Smith Period’s threshold is marked by two consecutive days where the minimum temperature is above 10degC and the relative humidity above 90 per cent for at least 11 hours, the research suggested that relative humidity only needs to be above 90 per cent for six hours before there is a significant blight risk."

amandstu

gk5000 wrote: »

There needs to be two consecutive days of high humidity. The UK used "Smith Periods" which specified 2 days with at least 11 hours greater than 90% humidity - but this is now being replaced by Hutton Criteria which suggests only 6 hours.

In Ireland Met Eireann use some formula - called something like "Irish conditions" to issue blight warnings.

I doubt if there is any blight spread in the current dry conditions, nor anything significant in the previous photo.

There may be little spots on individual leaves, but I don't think that's a problem. If the conditions don't allow it to spread then those leaves will die and the plant will continue to grow. I read somewhere that the tubers are still growing if 25% of the foliage is still there. I personally would not be a big fan of cutting off all foliage unless it was already dying and the stalk wilting.

• A Smith Period is at least two consecutive days where min temperature is 10 °C (50 °F) or above and on each day at least 11 hours when the relative humidity is greater than 90%.

https://www.fginsight.com/news/news/smith-period-blight-alert-set-to-be-replaced-17368
"While the current Smith Period’s threshold is marked by two consecutive days where the minimum temperature is above 10degC and the relative humidity above 90 per cent for at least 11 hours, the research suggested that relative humidity only needs to be above 90 per cent for six hours before there is a significant blight risk."

Nice research.

I read that as 90% for six hours on just the one occasion.Would you agree?

Not for two consecutive days.

We had those conditions in spades yesterday.

Alanstrainor

Some good information there. Cheers. I'm a complete first timer here, so my concern was losing the crop entirely. The potatoes were watered daily with a timed soaker hose, once morning and once in the evening. So watering definitely wasn't a problem.

I mean I could have been completely wrong with my guess that there was blight. But the spreading of it was rapid, and every day leaves were covered in new black spots, removing the leaves and checking the next day saw more and more spread. I hadn't sprayed the plants at all to prevent blight. So in my mind I was playing it safe.

amandstu

Alanstrainor wrote: »

Some good information there. Cheers. I'm a complete first timer here, so my concern was losing the crop entirely. The potatoes were watered daily with a timed soaker hose, once morning and once in the evening. So watering definitely wasn't a problem.

I mean I could have been completely wrong with my guess that there was blight. But the spreading of it was rapid, and every day leaves were covered in new black spots, removing the leaves and checking the next day saw more and more spread. I hadn't sprayed the plants at all to prevent blight. So in my mind I was playing it safe.

For blight you look on the underside of the leaf and there is a sort of circular darkening and softening with a kind of a mildewy effect that you will recognize after you have seen them.

There are other blemishes you can get and actual leaf spot can be serious but some are just minor although if the plant is just generally in a poor condition that would need to be addressed of course.

macraignil

Alanstrainor wrote: »

Some good information there. Cheers. I'm a complete first timer here, so my concern was losing the crop entirely. The potatoes were watered daily with a timed soaker hose, once morning and once in the evening. So watering definitely wasn't a problem.

I mean I could have been completely wrong with my guess that there was blight. But the spreading of it was rapid, and every day leaves were covered in new black spots, removing the leaves and checking the next day saw more and more spread. I hadn't sprayed the plants at all to prevent blight. So in my mind I was playing it safe.

Just to make things more complicated there are two types of blight early and late that effect potatoes that are caused by two different types of fungi. Your description sounds more like early blight to me with the mention of black spots. Less watering will also reduce the humidity and help slow the spread of the disease spores. I think you're overdoing the watering with twice a day.

gk5000

amandstu wrote: »

Nice research.

I read that as 90% for six hours on just the one occasion.Would you agree?

Not for two consecutive days.

We had those conditions in spades yesterday.

No, I think it means 2 consecutive days with 6 hours above 90% rel humidity and 10 degreees (instead of the previous 11 hours)

gk5000

Alanstrainor wrote: »

Some good information there. Cheers. I'm a complete first timer here, so my concern was losing the crop entirely. The potatoes were watered daily with a timed soaker hose, once morning and once in the evening. So watering definitely wasn't a problem.

I mean I could have been completely wrong with my guess that there was blight. But the spreading of it was rapid, and every day leaves were covered in new black spots, removing the leaves and checking the next day saw more and more spread. I hadn't sprayed the plants at all to prevent blight. So in my mind I was playing it safe.

Still doesn't look like serious blight - where whole leaves are black and stalks start to wilt. The spots may have been blight but it may or may not have spread.

However, watering twice a day could create the humidity conditions to cause the spread of blight. I would suggest a longer single watering no more than every maybe 3 days or more for spuds .

There is a school of thought for most crops : better to water rarely, but with a good soaking. This way it forces the roots to grow down searching for the water. Often and light watering may cause the roots to stay near the top of the ground.

amandstu

gk5000 wrote: »

Still doesn't look like serious blight - where whole leaves are black and stalks start to wilt. The spots may have been blight but it may or may not have spread.

However, watering twice a day could create the humidity conditions to cause the spread of blight. I would suggest a longer single watering no more than every maybe 3 days or more for spuds .

There is a school of thought for most crops : better to water rarely, but with a good soaking. This way it forces the roots to grow down searching for the water. Often and light watering may cause the roots to stay near the top of the ground.

Would that apply less for shallow rooted crops? (eg strawbs)

btw I thought once the blight was noticed it would always spread (but have b=never had the opportunity to test that as it is always so damn damp here and a spell of v dry weather would be needed to see if the blight's progress could be slowed)

I always cut down the plants at the first sign of blight (at least all the plants nearby)

gk5000

amandstu wrote: »

Would that apply less for shallow rooted crops? (eg strawbs)

btw I thought once the blight was noticed it would always spread (but have b=never had the opportunity to test that as it is always so damn damp here and a spell of v dry weather would be needed to see if the blight's progress could be slowed)

I always cut down the plants at the first sign of blight (at least all the plants nearby)

I'm guessing - but I think it only spreads if the conditions are right.
Sometimes you see round black spots on leaves - which I take to be blight which has stopped/died.

amandstu

gk5000 wrote: »

I'm guessing - but I think it only spreads if the conditions are right.
Sometimes you see round black spots on leaves - which I take to be blight which has stopped/died.

Well I am not an expert but I have read that once you have blight you just have to save what you have in the ground by removing the haulms. (the tubers will actually sit there quite happily and you can harvest them at your leisure even through the winter so long as they don't start to reshoot)

Maybe ,if you are in a dry part of the country a little blight might not spread so quickly ,I wouldn't know as here we are "blessed" with frequent rain even if not always actually blight weather (day long warm drizzle ).

As a compromise ,I have 4 or 5 separate beds and if one gets the blight I will dig it or cut down the haulms . The others I leave grow in the hope they may not be affected ,

But really they do all get affected one after the other and sometimes I feel not much is gained by not cutting them all down together as not a lot of extra growth is ever achieved


As for your spots on leaves that you think might be blight that has "stopped/died" I would be very skeptical. It might be blemishes from something else.

You should learn to recognise blight and then you would be better armed to know if that was the case.(but apparently there are two types of blight ,so unless they look more or less the same maybe I don't recognise both kinds either)