Avoiding tomato blight

It’s warming up and that means that those who grow their tomatoes in the open are dreading the arrival of tomato blight. The proper name for it is Phytophthora infestans and it’s a fungus which causes the fruit to brown and rot away – it’s the same organism as potato blight which means that the prevalence of Mill’s Periods will increase the likelihood of blight.

A Mills Period is when ‘environmental conditions are favourable to promoting the development of a vector (spores in the air or soil and insect populations) or disease’ – in other words, when the weather is both warm and damp. Because this promotes the spreading of the organism and because it travels both above and underground, the blight moves very fast, spreading from plant to plant and from plot to plot, wiping out crops.

There are things you can do to avoid it – like growing your tomatoes in a greenhouse where you change the soil annually to stop the organism overwintering in the soil. That’s what we do. If you want to grow tomatoes in the open, try:

1. Limiting watering – irrigate your plants only when necessary, preferably using a bottle watering or funnel type system and avoiding any spray of water landing on the leaves of the plant or on surrounding soil.
2. Try not to water in very windy weather as this can encourage water to spray around
3. Increase planting distances so that if one plant is affected, you might be able to limit the spread of the blight by removing others so that distant plants are not attacked.
4. Non-organic growers may want to try spraying with a copper treatment – but this has to be done before blight appears, so you have to gamble on spraying not less than 24 hours into what might become a Mills Period – it’s a tricky business.

Treatment is drastic – you have to destroy infected plants completely by pulling them out (carefully, so you don’t chuck contaminated soil etc over other areas of the plot) and burning them.

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Posted by The Allotment Blogger on Friday, June 18, 2010


Anonymous allotments4you.com said...

Luckily we haven't had tomato blight on our plot but I didn't know about the disposal process so thanks for pointing this pout as although I don't grow tomatoes on the plot my neighbour who uses my compost bin does so i will make her aware that in the event of blight she should not put them in my bin. Fires are banned on our plot so how should we dispose of them??

June 20, 2010 at 12:00 PM  
Blogger The Allotment Blogger said...

To be honest Tanya, that's a major problem that a lot of sites are wrestling with at present - and I'm being very careful about where I buy compost from, as a lot of the waste that is collected as 'green waste' is then resold as compost down the line, but could be packed full of such joys as blight. Not to mention of course, the recent horror that Green Lane Allotments have catalogued with such care, over the herbicides that have contaminated manure. If I couldn't have bonfires, I would probably bundle my tomato waste into binbags and send it to landfill, but it's a very poor solution at best.

June 21, 2010 at 8:58 AM  
Blogger Joanna said...

Would adding chicken manure to make the compost heap good an hot kill off the blight? When we had chickens we had temperatures of 70C and I would have thought that would kill off just about everything as this is pasteurisation temperature

June 21, 2010 at 9:13 AM  

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