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!

Labels: allotment-potato-blight, allotment-potatoes, allotment-tomato-blight, allotment-tomatoes

Allotment Potatoes

We’ve just put in our potato order:

First earlies – Accent
Second earlies - Kestrel
Maincrop – Pink Fir Apple.

I can’t tell you how good it is to say that! Placing a potato order really proves you’re an allotment holder. Of course there’s a lot of mythology and mysticism that surrounded the growing of the great British staple food, and some pretty confusing terminology too: all those earlies and chitting and blight and what have you. But it’s nowhere near as difficult as it sounds.

First – potatoes have two main problems: blight and slugs. We already know that on Duncan’s plot we have slugs (the evil little black keel slugs) so we shall be giving both plots a lovely dose of nematodes in the hope of killing the slugs before they get to the potatoes.

Second – the early and maincrop terminology is all about how long it takes from planting to harvesting so:

1. First earlies – ten weeks
2. Second earlies – thirteen weeks
3. Maincrop – twenty weeks.

Third – chitting is just the process of getting your potatoes to produce shoots and I’ll go into that when the time is right.

And while maincrops store much better (larger thicker skinned tubers) than the thin-skinned smaller early varieties, is the maincrop types that are likely to get hit by potato blight. Usually the earlies and second earlies have been harvested before it strikes.

Potato blight is properly called Phytophthora infestans and it happens in warm humid weather. The signs of blight are brown freckled leaves or leaves with brown wilted patches. The blight causes the potatoes to die in the ground but even worse because it’s airborne, it can get into your harvested potatoes and rot them too. Worst still, it spreads literally overnight – one day you have a crop, the next day you have a rotting stinking mess.

Fighting blight – don’t water the leaves of your potatoes, only the plants. Earth them up carefully and well so the spores of the blight can’t get in. If you see an early sign of blight, dig up that plant and burn it, but to be honest, if blight is within three or four miles of your crop, there’s little you can do to fight it, except grow earlies only, or blight resistant varieties.

Preventing blight – don’t leave a single potato, no matter how small, in the ground when you harvest – the spores can overwinter in the potato much easier than in the ground, where a frost usually kills them. Rogue (volunteer) potatoes left in the soil can infect the whole of a subsequent year’s crop. And rotate your crops – that way it should be three years before potatoes go back into the ground they occupied before, which gives the spores much less chance to hang on and ‘get them’. And store your harvested potatoes off the plot, if you possibly can.

Labels: allotment- potatoes, allotment-potato-blight

Oh dear, blight on the horizon?

So, there we are with our wonderful new plotshare, half of it already in excellent cultivation, and already the serpent has appeared in our little Eden.

I was making the most of Sunday’s sunshine when I looked along the row of potatoes our ‘official’ plotholder had planted with such care, and I saw a single potato - out of line but earthed-up - and with the wrong colour flowers just about emerging, to boot.

So I dragged our lovely plotholder, Duncan, out of his Sunday lie-in to tell me what he thought and we agreed that it's probably a rogue from the previous owner not clearing the bed properly which Duncan had earthed up by mistake. Being a remnant means it may well be harbouring blight, so out it came, I carried it home in a plastic bag and it's going in the bin tonight!

The dirty on potato blight

The first signs are darker or brownish patch and yellowing of the leaves, which may either curl up or turn black, then a white bloom develops on the underside as the foliage dies. The spores produced by the fungal bloom are washed down into the soil resulting in dark spots on the potatoes and reddish-brown stains like rust appearing right through the flesh. Potato blight can survive the winter as mycelium (tiny spores) especially if tubers are left behind in the soil after harvest. The fungus grows on shoots from these tubers the next spring and – in the nastiest possible way -produces asexual spores which are airborne to new crops during warm moist conditions.

Treatment

At the first signs of infection the top growth or haulms, should cut off and destroyed to prevent the spores being washed down to the tubers. All leaf debris should be removed too, and the entire blighted crop should be removed from the site.

Now we just have to wait and see if we got to it in time! Potato blight is the absolute pigging end in my opinion.

Labels: allotment-cultivation, allotment-potato-blight