tomato blight

[moonshadow]

i've just had to destroy the tomatoes in my greenhouse border, how do i prevent this recurring next year?

[Capsid]

It won't be easy, your options are to hope for a hot and sunny summer, spray with a fungicide, keep the greenhouse door shut.

[nerobot]

Prehaps grow blight resistant varieties?

Steven

[moonshadow]

i grew ferline outdoors and even that got it!

[moonshadow]

i should think we are all hoping for a hot and sunny summer after these last 2!

[Paulottie]

You can spray with Bordeaux mixture every fortnight. It will help stave it off but won't cure it. Approved by soil association.

Unfortunately I was away during later part of August and have lost 8 rows of spuds and 30 tomato plants. Very irritating.

[Alice]

What a shame Moonshadow. My beautiful tomatoes got blighted too. It's a problem I've never had before but this is the plan for next year.
Grow early maturing varieties (I believe blight doesn't arrive until August)
Limit the plants to 1 or 2 trusses and get them early.
I'll spray if I have to - but I don't want to
But I don't want to bin beauties like these again.

[womble]

Has anyone had a re occurrence of blight in a greenhouse after having it the year before?
Not I mean when blight is all around them, but early on. Because I've never heard of it.
Everyone also talks about diseases building up in greenhouses soil when you grow tomatoes in it, yet Mr Flowerdew said it took his, I think 15 to 20 years to build up.

[SueA]

I only grow tomatoes outdoors & the last couple of years they've been struck by blight because of all the wet weather. It's supposed to be rarer on greenhouse tomatoes because they are largely protected by the glass but as Moonshadow has had it & a few others too it's obviously becoming more widespread. If you don't want to use any sprays ( & they don't always work anyway!) the best you can do is dispose of any affected plant material (not in your compost) & thoroughly clean the greenhouse. The blight spores are not supposed to remain active on the surface of the soil but if you wanted to be doubley safe you could skim off the top couple of inches of the border & replace with fresh compost. I've been told by a couple of experts that it's O.K. to dispose of used grow bags which have had blighted toms. in them in your compost bin as the spores would not survive in the bag. Other things to try are to not get the foliage of your toms. wet when watering as the spores love the damp, wash your hands well if you remove any blighted leaves/toms. etc. as you will carry it to the next plant & try not to leave the greenhouse door open on damp windy days.

[womble]

The blight spores are not supposed to remain active on the surface of the soil but if you wanted to be doubley safe you could skim off the top couple of inches of the border & replace with fresh compost. I've been told by a couple of experts that it's O.K. to dispose of used grow bags which have had blighted toms. in them in your compost bin as the spores would not survive in the bag.

Could someone please explain how blight spores could then stay in the border soil in a greenhouse. Because I am not believing it.

[andrewo]

I'm giving up on my tomatoes next year, this is the third year they've got blight. They're outdoors and I'm against it for that. I think I will leave it for two years and see if the spores are out of the soil.

[Capsid]

Could someone please explain how blight spores could then stay in the border soil in a greenhouse. Because I am not believing it.

That's right, the spores are airborne and can travel from miles away or can survive in the affected plant. I suppose it is possible for diseased tomatoes to drop off the plant and remain undetected in the greenhouse soil. But I would think the tomatoes will rot over winter so it's more likely that the spores are blown in by the wind. It's the same with potato tubers; that's why it is recommended to buy new seed potatoes that are certified disease free each year.

[womble]

Thanks Capsid, thats what I was thinking.
Also for around 3 years I composted my blighted tomatoes and never had a problem, I only started throwing them away after being repeatedly being told I was doing it wrong. I'm not convinced you can't compost them (properly) either.

[Capsid]

Thanks Capsid, thats what I was thinking.
Also for around 3 years I composted my blighted tomatoes and never had a problem, I only started throwing them away after being repeatedly being told I was doing it wrong. I'm not convinced you can't compost them (properly) either.

Well, the spores come from somewhere, so there must be a place that they overwinter. I don't think they survive very cold conditions in the soil such as our UK winters.

The late blight fungus survives the winter in diseased potato tubers including those infected during the growing season and left in the soil, those discarded and not destroyed, or those stored for seedpieces the next spring. Potato tubers and tomato fruits discarded in late winter or early spring can be especially troublesome sources of the fungus because they do not necessarily freeze, so provide the spores that can infect the next crop. The presence of late blight one year seems to favor the occurrence of the disease the next year, probably because of these overwintering sources.

Source: EB0958 Late Blight of Potato and Tomato and Its Control in the Home Garden

ETA: later on in that article, it advises against composting since the pile may not get warm enough to kill the spores.

[Demeter]

Interesting, that article says:

"Do not place [infected plant parts] on the compost pile (back yard compost piles may not reach sufficient temperatures to kill specialized survival spores called oospores, if they are present)."

Detective Demeter scours the internet to find what the b***y hell oospres are anyway...

It appears (from what I can make out) that these oospores are "hardy" blight spores which only form if compatible strains of blight infect the same plant and then mate with one another and produce viable progeny. So this will only happen if both of the necessary strains are present, and even then is not certain.

If oospores are produced, they can survive away from the infected material (which other spres can't) and might be able to survive temperatures from -20 up to 43 degrees C. A compost heap or bin would normally exceed that temperature, I believe, at least if it is looked after "properly" - I think they can get up to around 60 degrees - although I guess if you just have a smallish pile in the corner which you never turn then it may well not get that hot?

Late Blight Workshop Paper - Fry
Phytophthora infestans

From all this, I would conclude that composting blighted material MIGHT cause reinfection the following year, but only if the right kind (or rather the wrong kind!) of oospores happen to have been produced and only if your compost heap does not heat up sufficiently for them to be killed... As others have suggested, it seems much more likely, if you get it, that this will be from airbourne spores, presumably from the bloke down the road who left his blighted tubers in the ground and allowed the spores to overwinter there... Grr.

(Anyway, it makes me a feel a whole *heap* better (geddit) about binning my tomatoes as I was only about 80% sure that they didn't have blight...)