Is it blight?

[timchorlton]

Hello,

I've just started gardening this year. I dug myself a small plot in the front garden (about 1.5 x 25 metres) and I've put some potatoes in (sorry, can't remember what type). They have been going just fine until a couple of days ago they started to look a bit limp. I gave them a water in the evening, but I've noticed some of the leaves at the base are going yellow and there are black spots on many of the leaves.

I've attached some photos.

Is this blight? If so, how do I deal with it?

[Flummery]

I don't think so. I think it's maturity. We all get a bit manky as we get older!

[timchorlton]

So have they had their flourish of youth? So fleeting - I think the first shoots popped up early may.

Do I just leave them or should I be thinking about harvesting them?

[Flummery]

Were they First Earlies, Second Earlies or Maincrop? If maincrop you often wait for them to die off on their owm so naturally they go a bit yukk. Genreally speaking you leave earlies 12 weeks, second earlies 14 weeks and maincrops 18 - 20 weeks - from planting time, so that will give you an idea.

[timchorlton]

Hi Flummery, I planted end of April with first shoots coming up early May. My plan is to dig up every other plant in the next week or two then leave the remainder for September. Does that sound like something that is a good idea of not? It's my very first time with a garden so this is my first attempt at anyhting.

[Nicos]

Every other plant???...hmmm- nah- I wouldn't bother, you'll probably disturb the neighbouring plants. I'd just take them from the end of the row when you need them for now. They'll store fine in the soil out of the light.
(If it turns out to be blight then you'll need to cut off the tops asap.)

[timchorlton]

Hi Nicos, given that I'm liking Flummery's 'old age potatoes' theory (based on nothing more than 'I hope it isn't blight')- if it did turn out to be blight - what are the unmistakable signs and how quickly do I need to react?

[sewer rat]

If the blackened areas spread the I would say it is blight - if it gets onto the stems then you need to lift asap. Sprays are available but they are preventive so cannot cure the problem. Blight spores are most active during what is known as a Smith Period - where for at least two consecutive days the minimum temperature is 10�C or above and on each day at least 11 hours when the relative humidity is greater than 90%.
A 'near miss' occurs when one or both of the above two consecutive days has only 10 hours when the relative humidity is greater than 90% and the temperature is 10�C or above. Note that a near miss is not recorded when temperature values are close to but not at the threshold value.
For more information you can google Blightwatch, where the disease is covered in more detail and they have an alert system where you can enter your postcode and they send out text warnings.

[Flummery]

However, lift a root and see how they are doing. That's what I'd do.

[timchorlton]

Hi everyone - what a helpful forum this is! I've been keeping an eye on them all week and they don't seem to be getting any worse. I'll take fummery's advice again and lift one of the sadder looking plants and see what lies beneath.

@sewer rat - I've just signed up for blight watch - can you believe it takes them 24 hours to gain access to the site! That can't help reduce the spread of a fungal disease!!

Thanks everyone for the help.

[Flummery]

I tend to work on the knowledge that vastly more people think they've got blight than actually have it. I'm a conservative gardener really (though not in any other sense).