Tomatoes and tomato blight

The current hot weather and last night’s storm have left us expecting to see Phytophthora infestans when we get up to the allotment. It’s the fungus which causes both tomato and potato blight and in both cases the warning signs are the same, brown marks on the leaves which spread quickly and then the tomato fruit will begin to brown and rot away. Underground, if it attacks the potatoes, they too will begin to rot and the blight can spread from one plant to another with astonishing speed.

The fungus is carried by wind and rain and takes a real hold during Mill’s periods which are times of warmth and dampness. It takes around three or sometimes four days of warm and wettish weather to allow the fungus to proliferate, so the first rule to obey during warm times is to water when necessary only and not to spray water on the leaves of tomato or potato plants – water the roots only.

There’s no organic treatment for this kind of blight, so we’ve been having a low level debate about whether to try to prevent/control it or not. We lost all our tomatoes on 235 last year to tomato blight.

To try and treat it, you have to destroy infected plants in their entirety – ripping them out and removing them from the site, preferably burning them to destroy the fungal spores which will otherwise lurk in the soil for years. You can also try to preserve your tomatoes by spraying them with a copper treatment (which is not organic) BEFORE the blight appears. This means that 24 hours into what might become a Mills Period you have to spray … and that’s what we’re debating, because you can always hope that dry weather will slow the progress of the fungus and that by planting with good spacings and removing and destroying any parts of the plant that have blight, you can save your crop – but only if the weather cooperates!

We haven’t reached a decision yet – remain organic and possibly lose our tomatoes or spray with copper and lose my organic principles? Watch this space!

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Posted by The Allotment Blogger on Friday, June 26, 2009

6 Comments:

Anonymous Amy said...

It is a difficult one, in the end I have decided to stick with the organic way and keep my fingers crossed.

One of the very non-organics on my allotments told me there was no point on sprayong tomatoes, they always get it anyway so they keep them in greenhouses instead.

June 28, 2009 at 12:36 AM  
Blogger The Allotment Blogger said...

We went for ruthlessness - removed half the plants to try and stop any spread, took off every sign of brown and crossed our fingers!

July 1, 2009 at 3:33 AM  
Anonymous Patrick said...

Tomato blight is always a big problem, and there's not a lot you can do about it. Growing them in a greenhouse helps a lot, but is not a complete solution. Spraying them with chemicals almost never helps much.

There are some things you can do to help by choosing the right tomatoes to grow. If for example you choose early varieties, they may produce tomatoes before blight appears.

Some 'wild' or 'current' varieties have some blight resistance, but these produce very small and sweet tomatoes that are not to everyone's liking.

There is one of these wild tomatoes, 'Tomatito de Jalapa' a number of us are growing this year, that is said to be totally resistant to blight. We are also going to start trying some crosses with this tomato, to see if we can get some more 'normal' tomatoes that are blight resistant.

If you get in touch in the winter, I can send some seeds or put you in contact with others who have seeds.

July 18, 2009 at 2:38 AM  
Blogger susanandstewart said...

I was told that there is an old law says you are not allowed to remove blight from your allotment.
is this true if so we must be allowed a fire to dispose of it.
sue

July 19, 2009 at 12:39 AM  
Blogger coops said...

very upset that i lost all my tomatoes this year in greenhouse and outdoors.Do i have to remove all soil from greenhouse for next year.

September 17, 2009 at 1:54 PM  
Blogger harrybrew69 said...

smiths period, not mills

January 6, 2010 at 2:49 PM  

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