Potatoes not looking too healthy! Advice needed

[SuburbanGardener]

Hi there!
After a successful summer in our veg patch, I decided to plant some Christmas potatoes in the same patch where we'd got a great crop of Spring/Summer potatoes. They were planted mid August & have been growing vigourously & earth up twice now. They are 'Duke of York' variety.

However in the last few weeks (since the cold snap), they are looking decidedly unhappy.










Any advice from those wiser than I? Have I lost them?

[Scarlet]

We'll the first pics look like slug damage, I'm not sure on the last pic, it may be blight with that black stem - how quick did it change from green to black?

" Christmas spuds" are very difficult to grow as they need to be kept somewhere frost free, not sure where you are but we've had a couple of frosty morning already. They really need protection. Most people that try for a couple of Christmas spuds grow them in buckets so that they can be protected when temperature are low.

[Zelenina]

Yes I agree. It looks like slug damage and late blight. If not blight then some other fungal disease, or frost damage if you've had any frost. They can recover from slug damage but not blight.

But all may not be lost. The advice I've read, and it seemed to work for me, is to cut off all the tops immediately, then wait at least two weeks so the blight spores on the soil surface die off, and hope that none get washed down to infect the spuds. Then you can harvest them.

Or you could probably leave them there until Christmas if the ground doesn't freeze hard, but there's a danger that underground pests will attack them. Although if there's only a small amount you might be better to dig them up now and cook them straight away before the blight gets a chance to rot them. They probably won't be very big yet though.

Have Spanish slugs reached the UK? Because as far as I remember, native English slugs didn't used to like potato tops, although the small underground grey ones loved to drill holes in the tubers.

But the fat orangey brown Spanish slugs that we have in Slovakia just love munching potato leaves, and almost everything else that people like to grow. I saw one recently eating another Spanish slug, and there wasn't much of the second one left, but I think it was probably dead before it was eaten.

[SuburbanGardener]

Thanks Zelenina & Scarlet,
We are on south London area & over last few weeks the mornings have certainly been very crisp .

I'll do some careful digging but suspect there aren't any/enough potatoes to harvest yet (I only planted mid August).

I'm not that keen on putting down slug pellets, so may try removing the slugs I can see and cut back the worst leaves. Any tips to control slugs with less invasive means?

Reading up on blight, I'm quite concerned that if I don't do anything, this will affect my crop next year - as once you have it, it sounds difficult to eradicate from the soil.

Thank!

[Kristen]

may try removing the slugs I can see

Problem will be the underground-ones, which will eat the tubers whilst still in-the-ground

Reading up on blight, I'm quite concerned that if I don't do anything, this will affect my crop next year - as once you have it, it sounds difficult to eradicate from the soil.

No, that won't be a problem. Blight can only over winter on plant material. Your own real worry will be if any tiny spuds get left in the ground and sprout next Spring. So long as you pull them up when you see them there is no risk for next year (more likely infection will come from nearby, from someone with less careful husbandry).

Don't compost any Blight'd parts of the plant nor tubers either though, as that may survive in the compost heap until next year.

Growing First Early spuds (next year) would help too - they will be up, and done, before Main Season Blight starts to be a problem. XMas spuds are the most tricky as they are planted and sprouting right at the time that Blight is at its worst ... any period of Wet and Warmth allows blight spores to "germinate" easily (so called "Smiths periods")

[SuburbanGardener]

Thanks Kristen.
Do you recommend I trim off the tops of the plant/shoots & hope the blight hasn't travelled underground?

Or should I go the whole way - cut my losses & dig up everything now (removing any new potatoes & tubers)?

Thanks

[Zelenina]

It looks to me more like blight than frost, especially with the dark patches on the stems. I can see even the green slug-eaten plant has a dark patch on the stem that will probably spread. But I could be wrong.

Blight is a worse problem than slugs, because if it affects the tubers, they will rot in storage. You need to cut off the whole tops if it's blight.

What I've read is that blight spores don't survive in the soil, only on living plant material. When the conditions are right it arrives on the wind and rain, so there's not much you can do about it, except for preventative spraying which can help if you don't mind the chemicals.

But it is better to rotate your spuds and not grow them in the same ground next year, to prevent other diseases building up. And make sure to dig up even the tiniest spuds, which might stay in the soil over winter and grow as volunteers next year.

The slugs! I go on slug patrol in damp weather or at night and collect them. I also attract them with small piles of wilted vegetation, which they love even more than fresh seedlings, and pick them off. Then they go in the salty bucket of doom i.e. lots of salt mixed with water. It kills them very quickly and seems the most humane method.

But only the Spanish ones, and sometimes the small cream and grey field slugs. I leave the leopard slugs alone, and I relocate the big Roman snails to a wild patch when they occasionally take a fancy to my veggies (we don't have the common British garden snails here). You can't be that selective with slug pellets.

You have to make it VERY salty. More salt than water. The last time I thought I'd made it strong enough, but I found one merrily crawling around the rim in the morning, and other escapees gliding off in all directions.

But if it's a cold winter a lot of them will die anyway, because they're less tolerant of cold than native slug species.

Well Kristen said most of it a bit faster than I did

[solanaceae]

Definitely looks like the ol' blight to me.

Looks like the infection is too far progressed to save the plants.

If you plan on doing the same next year then my advice would be to spray the plants with an organic fungicide and make sure you remove any infected material asap. I've been doing that this year and my tomatoes and potatoes are still thriving.

[Zelenina]

Yeah, your best bet is to dig them up and use the space for garlic, or overwintering onion sets and shallots, or broad beans. Or maybe you can get some plants of winter brassicas e.g. kale and sprouting broccoli.

[SuburbanGardener]

Thanks all, I've taken a good look & they certainly aren't in a good way.
So have dug then up & will dispose of the foliage, etc..

Ahhh we'll you don't know if you don't try, it's all a learning experience

[Kristen]

Do you recommend I trim off the tops of the plant/shoots & hope the blight hasn't travelled underground?

The conventional advice is to cut off the tops (dispose of them, don't add them to your compost heap) and then wait [at least] a couple of weeks before harvesting the spuds, the idea being that any spores that fell on the ground will be dead and when you harvest the spuds the spores won't infect them (which would cause them to turn black and rot, in storage). You could also harvest them as you want to eat them, rather than risking harvesting them and them becoming infected, but in that case you run the risk that slugs might attack the tubers in the soil. IME the spuds keep better in the soil, provided they don't get eaten!

If you have dug them up then best to use them quickly, in case they are infected (and start to rot, as a consequence). Did you get a reasonable crop?

[Martin H]

Latest evidence is that the pathogen can only overwinter in seeds and tubers, so it's safe to compost the tops. Just be vigilant for any growth in the spring from little tubers that you missed, dig them out as soon as you can.

[Kristen]

Latest evidence is that the pathogen can only overwinter in seeds and tubers, so it's safe to compost the tops.

Interesting, not seen that advice ... I wonder what happens if the Tops are composted and someone throws some "unwanted spuds" on the heap too?

Personally I prefer not to put anything diseased onto the compost heap.