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Potato blight


by Pippa Greenwood

The only thing to do when blight has affected your potato crop is to chop the haulms down to the ground and burn them so the spores don't overwinter.


Potato leaf affected by blightPotato blight, Phytophthora infestans, determines the quality and quantity of our potato harvest. We grow our own spuds every year, but harvest them in varying quantities, depending on whether or not they've been affected.

The fungal infection is triggered by warm, wet weather, and if the spores are present in the air or the ground you can pretty much guarantee problems.

So it's with a good deal of trepidation that I look at the rather unhappy looking foliage on my maincrop potato plants. We've already eaten and given away pretty much an entire row of one of our early varieties, but it's the maincrop potatoes that are worrying me (yes, I'm thinking ahead to Christmas lunch already). Small brown patches have appeared on the foliage and early signs of leaf chlorosis.

But it might not be blight, so I don't want to act too soon. There are several other, far less significant problems, which can cause similar symptoms, and - even after 20-something years of looking at infected, infested and otherwise miserable plants - I'm still unsure on occasion, especially with very early symptoms.

The only thing to do when blight has affected your potato crop is to chop the haulms down to the ground and burn them so the spores don't overwinter, reducing the chances of your crop being affected the following year. You then need to harvest the potatoes (big and small) before it rains, otherwise the fungus will reach them and render them inedible and rotten.

Luckily, the other day I was sent a potato blight testing kit - similar to a pregnancy testing kit. So my next job is to go out to the vegetable patch, cut off a small sample of affected foliage and pop it in the little kit - I'm nearly as nervous about this as if it were a pregnancy testing kit!

A positive result will involve hours of work, but a negative result means I know I can safely leave the haulms, allowing larger tubers to develop. At least I'll really know where I stand!



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Talkback: Potato blight
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Gardeners' World Web User 31/07/2008 at 22:04

And then it goes on to destroy your tomatoes! Blight really is the word!

Gardeners' World Web User 01/08/2008 at 11:16

Where are potato blight testing kit available from and at what cost?

Gardeners' World Web User 02/08/2008 at 20:53

I used to be a fan of Belle de Fontenay but if there is any blight about they will get it. So it really pays to plant the latest varieties, Orla is good but is thin skinned so cannot be left long in the ground because of slugs. 'D T Brown' gave away Emerald Vale this year as a trial and they have been fantastic so I would highly recomend them.

A few years ago the head-gardener from Heligan Vegetable Garden came to give talk, apparently it is impossible to grow main-crop potatoes in Cornwall organically, so maybe if blight has been a problem you just have to compromise and use a suitable spray?

Autumn fruiting rasps are cut down in the spring and a new cane grows and fruits in the same year. Summer fruiting have the old cane removed after picking and the new canes retained and tied in for next year.

Gardeners' World Web User 06/08/2008 at 12:35

The potato blight testing kits are available from the Pocket Check website, they were featured last month on BBC 4's Gardeners Question time. I see that they are also being offered as a competition prize on the Win page of this site.

Gardeners' World Web User 06/08/2008 at 20:57

Can anyone tell me if you can grow a younge cherry tree in a container and if so what to do.

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