Potato Late Blight

[Jayb]

Watch out Late Blight is about, spotted some suspect leaves on my Pink Fir Apples yesterday. I picked them and popped them in a plastic bag overnight, it's developed at quite a pace. Just in time for a wet week, Oh joy!

It's been much dryer here than usual, but still two Full Smith Periods 13th and 14th June and 21st and 22nd June, plus a near period 28th and 29th June. Obviously it was all it needed to get a hold,   particularly on a vulnerable variety like PFA.

[Jayb]

[BarriedaleNick]

Today feels like a blighty sort of day.  Warm and muggy here in London.  Time to spray everything blue!

[Digeroo]

This is bad new indeed.

We also had a full period 14th and 15th though it has been so dry I cannot remember the wet days.  Not clear why this did not trigger the blight but it was very cold the next morning. It says it was minimum 8 but on the ground in the middle of a field it was much much colder so perhaps that prevent it. 

We have gone a lot longer this year without problems.   I am hoping that we already have quite a few potatoes. 

Our site is normally amongst the first to show signs but so far fingers crossed we are clear.  I am pleased to find I have no potatoes up wind on one plot and a resistant variety on the other.   

[Robert_Brenchley]

I'm hoping to get away with it a bit longer, but you're right, it does feel that way. After last year's good summer there shouldn't be too much blight on the site, which may be why we've got away with it so far. The longer we go without it, the more chance there is of getting reasonable tubers off susceptible varieties. I've discovered that minute TPS tubers will overwinter and produce plants, but I'd far rather have decent sized ones!

[sparrow]

Am really hoping I escape for a bit/totally. Most of my Charlottes won't be ready for another 4 weeks because they had to go in late.

It did feel properly 'blighty' today though - humid and with mizzle all evening. A brisk drying wind tomorrow would be great.

[Digeroo]

We have just had a full smith period,.  Yesterday we had 24 humid hours and today will be another one. So three days in a row!  I am sure the blight is gathering for attack.



More space for the squashes and pumpkins.

[Jayb]

There is some suggestion that the more modern and aggressive strains of Late Blight can function in broader conditions, so a Smith Period can only be a guide and own local conditions should be noted with this in mind. I think as well the map for listing incidents is not a true reflection as many of those reporting will be commercial and using sprays not available to home/allotment growers. The incidents of LB were they known from allotment/home gardeners would be much higher and perhaps a truer reflection.

Blightwatch  http://www.blightwatch.co.uk
Fight Against Blight - Blight Incidents  http://potatoes.ahdb.org.uk/fight-against-blight/blight-incidents

[Jayb]

Some recent pictures
These two pictures are LB just starting off, the first just a small spot and easy to miss from the top view, then underneath it looks more obvious and typical.

[Jayb]

Here's a patch obviously more developed, the area is spreading through leaf and veins, again the underside too.

[Jayb]

This first leaf is majorly infected following wet and warm conditions, if left the infection would soon kill the plant leaves and stems, it would also rapidly be producing spores to infect other plants too. The second picture shows how drips of water holding on a leaf can often give the right moisture conditions for spores to incubate.

[gray1720]

So what can you get for it these days? I can finish my Dithane stocks (incurring the wrath of organic mangement), or.... what? I believe Bordeaux Mixture is now off the market, so which nasty copper salts are left?

Adrian

[Ellen K]

^^ I've seen copper fungicides in Wyevales this year.  Or you could get a recipe from the internet and buy copper sulfate and lime frim ebay and have a go yourself.  Dithane is still for sale on Amazon.

The potato websites seem to agree that the more important thing in when you spray rather than which fungicide you use so be quick if you haven't already done it.

Oh Jayb, virtual hugs to you :-(

[Silverleaf]

You know, I'm still confused about LB. I keep checking my plants almost obsessively, but I can never tell whether I need to be worried or not.

Some leaves have little brown patches, but they are a redder "dry leaf" brown and not a chocolatey "rotten leaf" brown. They are dry and crispy, no fuzziness underneath or anywhere else, and they aren't spreading fast.

I'm just not confident in identifying it, and that means I worry that I have it without knowing. I've only seen it once in person, at the meetup last year.

[squeezyjohn]

I know what you mean Silverleaf ... I'm always thinking I have it when the leaves are just dying back ... but there really is no doubt in my mind when I actually get it badly!!  It's looking for those early signs I have the trouble with.

I'm afraid all my potatoes and tomatoes are bright blue now ... bang goes my organic gardening credentials!!

[Silverleaf]

I'm rather glad in a way though, since my lack of knowledge is because I've never had LB. I know I've totally jinxed it saying that, and I'll probably go out later to find my potato bed nothing but a brown mush, but there you go.

It'll happen sooner or later.

[Digeroo]

Went to buy some Bordeaux mixture there is no alternative on sale.  With three full criteria days in a row and today no better I am sure my tomatoes are doomed.

Any suggestions as to alternatives.

Wyevale have a copper product but it is nearly twice the price of last years Bordeaux.   It says it is for adjusting for copper deficiency in the soil.  Huh?

[Ellen K]

Digeroo: if you search on ebay for Bordeaux Mixture in Weed Pest Control, there are a few listings for a DIY kit, starting at about £3.50.

Here you go:

http://www.ebay.co.uk/itm/121695469519?_trksid=p2060353.m1438.l2649&var=420697631758&ssPageName=STRK%3AMEBIDX%3AIT

4 packs sold in the last 24 hours

[Jayb]

You know, I'm still confused about LB. I keep checking my plants almost obsessively, but I can never tell whether I need to be worried or not.

Some leaves have little brown patches, but they are a redder "dry leaf" brown and not a chocolatey "rotten leaf" brown. They are dry and crispy, no fuzziness underneath or anywhere else, and they aren't spreading fast.

I'm just not confident in identifying it, and that means I worry that I have it without knowing. I've only seen it once in person, at the meetup last year.

If you've been checking your plants daily and already have brown patches that aren't changing much it is unlikely they are LB (unless it has been particularly dry for some time as it is then harder for LB to make progress). If you do notice something new overnight keep an eye on it, if it is a wet day it will likely have enlarged by evening. You can always pick off a suspect leaf, wet it and place in a sealed plastic bag, put it somewhere warm to incubate, overnight is ideal. You should be able to tell by morning, if you are still unsure leave for a few more hours. LB on leaves can look a bit different depending on conditions and early signs can be difficult to spot, but if you do see some and remove infected leaves it gives a little longer for the rest of the crop.

Although I think I must live in Late Blight central, I don't spray, I did up until a few years back as I always used to think if I don't harvest potatoes for me then I'll end up buying some and they will have been sprayed with a lot more than I would have used. But as all we are left with now are copper sprays I'd rather not use them on my veg plot. I'm growing 3 blight resistant potato varieties this year so hopefully will have something to harvest from them later on, plus I've got some trial varieties and might be lucky and find one that is resistant.

[bluecar]

Hello Jayb.

Great pictures showing the early stages of LB. Most of the websites have pictures that show it at a much later stage.

[Digeroo]

I will not bother with potatoes hope to have enough already and have a resistant variety.  I was confuse about blight a few years ago, and I would say if you are confuse you have not got blight. If you have totally devastation then yes that is blight.   

Might spray my tomatoes though.