[rwhittington]

Hi,

Long time lurker - first time poster.

After 6 months of planning we decided to give vegetable production a go, and this is our first "serious" attempt at producing a harvest, so forgive me for any elementary errors here.

Last weekend, I sprayed our potato crop with some anti-mildew fungacide (Milraz MZ), as we were told by the neighbours that we should always do it this time of year (we live in Northern Spain).

Following some heavy rain and nasty humidity this week, I checked our spud patch and one of the plants has a few "black" sections on some of its limbs. I've spoken to the resident experts here, but the advice goes from "tear off the affected branches" to "rip out the affected plants" to "leave it and spray it again in 14 days".

Colour me confused.

Could anyone here point me in the direction of a good guide for spud mildew on this site, or give me some general advice, I would be greatly appreciative!

All the best,
Russell

[BabbyAnn]

It sounds like Black Leg - as far as I know, there's no cure for affected crops 

http://www.gardenorganic.org.uk/factsheets/dc3.php

[mumofstig]

here's the Potato Councils disease help sheet

http://www.potato.org.uk/department/knowledge_transfer/pests_and_diseases/viewer.html?type=diseases

[rwhittington]

Crikey! Thanks for the heads up there BA & MoS! I'll be ripping it out as soon as I put the laptop down.

The potatoes were a gift from our neighbour, so I'm hoping they're not all affected.

[rwhittington]

Okay, just removed about 5 affected plants, and I've got a general question about going forward with this:

1) About 40-50% of the remaining plants have blackening on their stems. It's not quite rotted, or anywhere near as bad as the 5 or so I've removed, but should I just rip them out too?

2) As I said in the original post, I sprayed my entire crop with a fungicide last weekend, before any real signs of Black Leg appeared. I've got it in my diary to do it again next weekend, but in light of the above, should I spray them again as soon as possible, or are those already affected beyond saving?

3) For next season, what should I be looking for when I buy potatoes for planting? Are there any give away signs for Black Leg? It sounds as if it's the biggest problem for potato crops in this region, so if anyone can suggest the warning signs I would be more than grateful.

Cheers

[Yorkie]

1) I would probably get them out, as it is a fungal disease so can spread.  However, see whether others would do the same thing.

2) Don't think so.

3) It doesn't normally come in on the tubers, but arrives through the environment.  Just make sure you get certified seed potatoes i.e. from a proper supplier rather than reusing cooking potatoes.

[mumofstig]

the RHS page on blackleg has some advice and shows a few resistant varieties, which may be a good idea if your site is prone to it.

http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=223

[rwhittington]

Buffff... depressing! I've taken a few more out and I'll monitor the rest over the coming weeks. Thanks for all the help, by the way. The RHS website is superb!

We bought this place last May, divided the land in two, and we're using the south-side as the veggie plot (600m²) and the land hasn't been used in nearly 10 years, so I dread to think what other kinds of nasty are in the soil. 

[rwhittington]

Further developments:

80% crop ruined; I've removed all infected plants and I've sprayed the remainder with fungicide, though my breath is not held!

Carrying the bags to the tip was pretty depressing.

So, more questions:

1) The potatoes from the infected plants, are they edible, or do they need to go too? The seeding potatoes for all the plants were ruined (some were like custard!), but there are a number of good-looking spuds under the soil, are they bad to eat?

2) What do we do with the land now? Double dig it all over and use it for something else immediately? Or dig it over every once in a while and leave it for next year?

Thanks again!

[Yorkie]

1. I guess this will depend on whether the fungal spores washed down to infect the potato tuber or not.  Perhaps get them up, store them in a dark, dry and airy place, not touching, and keep an eye on them?  See what others say as I'm not 100% sure.

2. I think black leg is potato specific so you would probably be OK with plants from other families (i.e. not tomatoes)

[DD.]

It is potato specific and can survive in the ground over winter. Crop rotation is of paramount importance here.

Where are your seed spuds cultivated?

[shokkyy]

If the land hasn't been used for 10 years, there really shouldn't have been anything still lurking in the soil, so I'm kind of surprised that you'd get such a devastating attack of black leg.

[JayG]

I lost a few Lady Christl plants last year from what I think was blackleg; I'd never seen it before on my plot so I guess there has to be the possibility that it was imported with the seed potatoes (even though they were "certified Scottish seed potatoes".)

Some varieties have more or less resistance to the many diseases they are unfortunately prone to, and I don't know what the situation is where you live or what varieties you have to choose from (worth trying to find out if there are similar organisations to the British Potato Database and a system of health certification I would think.)

I'm pretty sure that blackleg is specific to potatoes so you should be OK with anything other than related species.

If the spuds look sound I'd certainly eat them (probably start with just one to make sure there was no tainting of the flavour!) 

[Aunt Sally]

I hate to put a spanner in the works but potato blackleg is a bacterial infection NOT a fungal one.

[Yorkie]

Ah.  I think I thought they were the same thing 

I know viral is different from bacterial.

You learn summat everyday, thanks Aunt Sally.

That might explain why the anti-fungal spray had no effect, I guess!