[Yana]

Ive been flowing the threads with regard to potato blight but need guidance please.......

It looks very much like I have blight ( informed today that it is at the other end of the lottie plots so bound to get to me), the leaves have developed brown spots and some of the plants seem to have collapsed and the leaves are yellowing.
One thread said to take the tops off, burn them and leave the potatoes in the ground for 2 weeks before lifting the potatoes. As I have grown my potatoes through layers of straw and grass cuttings, do I burn this as well?
I don't want to spread the disease any further so if it is to burn the straw, grass and tops of the potatoes (leaves), then that is what I will do.

Just when things seem to be looking up with the good weather predicted ...... 

[mondaysoff]

Hi again, just read your post. I also have an allotment, only had it 3 year, so relatively new. All 31 plots seem to have suffered the same fate with potatoes and tomatoes. Speaking to an old timer down there yesterday, he said to me you can compost as well as burn. Everything else you mentioned seems to be the case, chop down, leave for 2 weeks then dig up.

Next year I am going for blight resistance strains.

[mumofstig]

Brown spots on their own are not blight, it's the fungal infection that you can see around the spots that confirms blight or not. Just one collapsed spud in the middle of others is probably black leg - pull that one out straight away.

Some clear photos of blight in the link here
http://chat.allotment-garden.org/index.php?topic=56717.msg1070250#msg1070250

I wonder if the potato tubers will have the same amount of protection under straw as they would under soil 

[Salmo]

The basic principle is that you remove the tops to stop so that no more spores are produced.

The important thing is not to disturb the soil so that any spores lying on the soil are destroyed by drying and sunlight and do not infect the potatoes under the soil.

The act of taking your grass/straw off may well take away any protection the potatoes have.

Advice always seems to involve burning potato tops. That is a very difficult job. Better to bag them and seal the bags. After a week or two that material should be fit for composting as no spores will survive if there is no live material.

The reason not to compost them immediately is that tops lying on a heap will still produce spores until the tops are dead. If you can be sure to seal the heap then it is OK.

No doubt there will be critics of putting infected tops on the compost heap at all but BLIGHT SPORES CANNOT EXIST WITHOUT LIVE POTATO therefore will not be carried over inpotato tops and the compost will not infect next years soil.

What you must avoid is either putting infected tubers in the compost heap, that includes peelings and lumps cut off, as they may survive the Winter and infect next years crop.

Neither should infected tubers or small potatoes be left in the soil. Any that grow in the Spring are a primary source of blight and should be dug up, cut off or "Roundupped", rather than left to produce a bonus crop.

[sunshineband]

I agree with you Salmo 

I have often wondered though how the volunteers spread the bacteria exactly?

Does anyone know?

[fatcat1955]

BLIGHT SPORES CANNOT EXIST WITHOUT LIVE POTATO therefore will not be carried over inpotato tops and the compost will not infect next years soil.

Jury is out on this. Belief is that the new strains can overwinter in the soil, so i would play safe and take them to the tip.

[Salmo]

I agree with you Salmo  

I have often wondered though how the volunteers spread the bacteria exactly?

Does anyone know?

If a tuber is infected with blight and does not rot completly rot it may grow in the Spring, either as a groundkeeper or in a compost heap or farmers dump heap. The shoot that grows will develop blight and be a source of infection for neighbouring crops.

[Salmo]

BLIGHT SPORES CANNOT EXIST WITHOUT LIVE POTATO therefore will not be carried over inpotato tops and the compost will not infect next years soil.

Jury is out on this. Belief is that the new strains can overwinter in the soil, so i would play safe and take them to the tip.

Theoretically sexual reproduction between different strains of blight can take place and produce oospores which can last in the soil for many years. It happens in Mexico but has never been seen in the UK. If it ever happens we are in deep potato trouble.

[Yana]

Sounds very technical Salmo.
The brown spots don't have a yellow outer ring so maybe I am worrying unnecessarily.
I'll pull the collapsed plant out as Mum suggests.
Several lottie holders have said that their potato yield has been poor this year so even getting a few potatoes is a bonus, whatever size they are.