Tomato blight

[LilyL]

I had an appalling tomato crop this year - in fact, I didn't have 1 tomato! All the plants had loads of tomatoes and then the stalks of the plants went black, which spread to the tomatoes themselves.
I was told it was Tomato blight. How did that happen, did I over water, is it airborne or in the soil?
I have been told I should sterilise the soil or I won't be able to use it again for at least 2 years - is this correct?
Any advice would be gratefully received.

[LilyL]

[Plot 18]

The blight spores come in the wind once there is wet and warm weather there's not much you can do to prevent it, growing in a greenhouse or polytunnel gives some protection.

So far the varieties of blight we have in the UK do not overwinter in soil, only on living plant material in or on the soil. So make sure you remove all trace of the tomatoes and any potatoes you grew (It's the same disease on potatoes)

Don't sterilise your soil, the sorts of things sold for doing this kill off a lot of beneficial soil organisms. It's not advisable to grow anything in the same place again the next year, good crop rotation avoids this. 

[Tee Gee]

I agree with plot

You could try ring culture as seen here

http://www.thegardenersalmanac.co.uk/Data/Ring%20Culture/Ring%20Culture.htm

[winecap]

Or try a blight resistant tomato. For outdoors growing I only succeed with very early tomatoes like red alert or blight resistant ones like crimson crush and mountain magic. All my other varieties stay in the greenhouse. The greenhouse rarely has a blight problem so long as you don't spread water all over. Water direct to the roots.

[galina]

As said before, growing in a greenhouse largely prevents it, providing there is enough ventilation.  I leave doors open and have roof vents.  It can be more difficult in a polytunnel, where tomatoes should be grown towards the centre, to avoid condensation drips.  If you can grow in pots under the eaves of a house roof against a south facing wall that is also quite a good position with warmth for earlier ripening and shelter from the prevailing breeze. 

Blight spores start blowing when it is warmer than 10C and very damp for 2 days or longer.  The first sign are black spots towards the edges of the leaves.  This happens before the stems blacken.  When you see black spots and the weather forecast is for hot and sunny, leave them, but if it is going to be damp, then harvest all full-size green fruit and ripen on the window sill.  They will colour up.  Not quite the same, but at least you will get some fruit, if you act promptly.

Best advice you got already, early varieties and blight resistant varieties and start early.   

[Vinlander]

All good advice, but LilyL is at the first post, and might have been spray watering - which is just the best possible invitation to blight. As Galina says, even in a greenhouse the spores are always about - and it's mostly the dryness (and drying heat) inside that protects the plants.

I once tried to very carefully water-spray aubergines under cover to control spider mite - it worked,  but the tomatoes nearby immediately got blight.

Always water with a trickling hose to the soil right next to the plant, especially outside - no splashing at all. It's even better to give each plant an empty pipe or cut-off bottle sunk into the soil so all all splashing is 20cm underground.

If your plants are well established outside then try not to water them at at all unless it's a scorcher (sadly 2006 was the last one). We aren't growing in Spain or Italy - our soil is always damp (unless your garden is a sandhill). You will rarely see an established tomato wilting outside - and the tomatoes will taste better. Why do you think our tomatoes taste better than the shops'? It's because the shop ones taste of water.

Ventilation is important even outside - if the wind can get between the plants they will dry quicker and that can stop the spores in their tracks. Get to know your prevailing wind and if you can't cover the plants against the rain it carries, then open them up so you can use the wind to dry them afterwards.

An open-sided, sloping clear cover (awning? Car port?) can be effective against anything except days of horizontal rain - even slightly dryer plants plus excellent ventilation can do the trick.

Cheers.

PS. in a really bad year nothing works, even the chemical sprays failed the people who like them (and always made their toms taste of rotting cabbage) but the last really bad one was years ago when the blight mutated before a damp summer.

[Digeroo]

We started our allotments on a site which had never grown potatoes or tomatoes so it could not have been in the soil.  And got blight the first year.    They do not grow potatoes near us either, soil is too alkaline so they end up with scab, most fields are rape seed or wheat with a few fodder maize. 

[Tee Gee]

rape seed is often a host plant for blight

[johhnyco15]

blight watch is a good service to join its free put in your post code  and it emails you when blight is likely in your area then i spray  with copper mixture which can be bought from any good garden centre here on the sunshine coast we dont normally get blight until late sept/early oct so we are very lucky  hope this helps

[Plot 18]

rape seed is often a host plant for blight

I've never heard that said - where did you find out about that?

[ancellsfarmer]

Regarding the infection with late potato blight, my understanding is that the spores arrive with rainfall, are carried at high altitude and may be in fact from areas of contamination hundreds of miles away. These could be the result of harvesting/cultivation in continental Europe or Eire. Some protection may be created by 'roofing over' outdoor crops, to enjoy similar protection as greenhouse crops, in a poly tunnel or simplified large cloche arrangement. Last year (2017) I succeeded thus, until the crop had grown above the height of the cover. This coming (soon) year , the plan is to grow "espalier" fashion, to keep the height within the cloche size, but accomodating the plant horizontally(at 60 degrees of inclination).This will be at the cost of limiting to 3 or 4 trusses per plant, which should be ripened by Sept.