Spots on potato leaves

stiggy · Post by **stiggy** » 28 May 2008, 15:54

Hi,
I'm new to growing my own crops - in fact it's my wifes 'job' to do all the planting and growing...

...it's my 'job' to do all the digging, building and general groundsman etc....

...but I thought I'd ask - hope you don't mind a newbie asking for help straight away - but we have little rust/brown spots on our potato leaves... only small ones, but some leaves are covered in them.

I expect it'd be more useful to have a photo, I'll add one later when I go down to the house, but any ideas of what this could be?

I have been looking online, and all I can guess at would be a mineral deficiency like manganese or potasium?

Post by Mo » 28 May 2008, 16:30

It might be the dreaded Potato Blight, cause of the Irish Famine.

There are things you can spray (copper based fungicides) but make sure you wear a face mask and don't breathe it in.

If it is blight you don't want the infection to get onto the spuds or they will go slimy and smelly and won't keep. So make sure you earth up well, remove dead leaves. When you harvest, cut off the tops and remove them carefully so that you don't shake the spores all over the tubers. Then look at them carefully,and use any you are doubtful about first.

If it isn't blight you'll get it later in the season, so do that anyway! Last year was bad,with all the wet weather.

stiggy · Post by **stiggy** » 28 May 2008, 19:40

Hi again,
ok... I took a couple of photos in the hope I can pin this down to one thing that I can (hopefully) sort out before it's too late...

These are the small spots..

And this is what happens when it gets bad..

Pleeeease tell me I haven't lost my crop!?

Thanks for your help!

:-D

Meanqueen · Post by **Meanqueen** » 29 May 2008, 10:07

Hi Stiggy, just looking in my library book for you, The Vegetable Expert by Dr. D.G. Hessayon. It could be as Mo says, potato blight. It says it is the most serious potato disease, capable of destroying all foliage in a wet season. First signs are brown patches on the leaves, look on the underside of the leaflets, each blight spot has a white mould fringe in damp weather. Says no treatment once the desease has taken hold. Prevention, spray with Dithane in July. Looks like it could spread to other plants, so destroy infected leaves. The picture in the book looks like yours.
If there is yellow patches and black stems this is frost damage.
If there is yellowing between the veins which turn brown this is magnesium deficiency, feed with multi tonic.

That's all it says, try this site for more info
http://www.allotment.org.uk/vegetable/p ... blight.php

Ilona
:cry:

Post by Mo » 29 May 2008, 11:45

That picture does make me think 'blight'. Earth up well (using clean soil from elsewhere in the garden possibly). Take off the worst leaves, and hope.
You've got it very early in the season!

stiggy · Post by **stiggy** » 29 May 2008, 11:53

Thanks for your replies...

... I checked, no whiteness under the leaves - the rusty spots are same either side.

I'll do what you say and earth up well, I've added some nutrients already and watered those in - I'll try to find a copper based spray and use that - see if it makes any difference.

What a shame for our first crop of potatoes!

:cry:

morph · Post by **morph** » 29 May 2008, 12:01

Hi there

I also lost my first crop last summer....leaves just wilted and died in the summer.

However, when I dug out the barrel to wash and prepare for this year, there were around 30 potatoes in there, so I was pleasantly surprised, that we were still able to have a few meals from them!

Meanqueen · Post by **Meanqueen** » 29 May 2008, 16:57

My potatoes look alright up to now, but I have run out of earth to 'earth up'. It seems a bit wastefull to use bought compost, I have some home made compost but it has a lot of hoss poo and wood chippings in it, it has been rotting since last summer. Would it be alright to use this? I read somewhere that you can use grass cuttings, is this ok? Can't find the answer to this in the book.

Ilona

Post by Mo » 29 May 2008, 21:40

My soil is sandy so I mix grass cuttings with the soil. I think they said on gardeners question time that potatoes grown on sandy soil are prone to scab (yes, mine do) but the bacteria or fungus from the breakdown of the grass competes with the sort that cause scab, and I've found I get cleaner spuds with lots of grass in.
But anything that keeps the light out and gives the spuds something to grow in should be ok. If I remember right, some advocate a no-dig method, seed potato on the soil covered by heavyweight black polythene with a slit for the stems, and just lift the plastic to harvest the crop. This was a while ago, so maybe it hasn't caught on for good reason.
Don't know how old the poo-compost would need to be.

Post by Mo » 29 May 2008, 21:42

Grass cuttings alone would rot down small. Also get very hot.