Thursday, 3 July 2014

Alternaria

Alternaria species - also known as Early Blight.  Not a problem I was anticipating having in the vegetable patch but this is one of those occasions where what I want doesn't count for much.

On Tuesday evening I noticed some very sick looking leaves on the Maris Piper haulms. I harvested a couple of plants and the potatoes were outstanding, much better than the Maris Bard I've been digging up from the other end of the bed.  The thought of blight crossed my mind but it's too early ... and it might be lack of water (no rain here for nearly four weeks) ... or the fact that our visiting pheasant family rampage through the foliage on a daily basis!





By yesterday morning I knew it was early blight and it had raced through the bed.  My pictures aren't brilliant but I could see the tell-tale circular lesions, exactly the same as on the the Potato Council of Great Britain factsheet, which doesn't really have a lot to say on the problem:

Early blight, caused by Alternaria species (spp.), was previously considered to be a risk only to potatoes grown under a warmer, continental climate. Indeed, early blight is the most significant foliar disease of potatoes in the USA, Asia and Africa. Recently, early blight has become far more widespread in mainland Europe, Scandinavia and, increasingly, in GB. It has always been possible to find Alternaria spp. lesions on GB potato crops, although the disease did not develop early or severely enough to affect crop yield or quality. However, in the warmer summers of 2010 and 2011, earlier and more severe effects of early blight were observed on several crops of susceptible potato varieties. Several factors may have led to increased incidence of early blight in GB potato crops:
Climate change, resulting in warmer summers
Growing of more susceptible potato varieties
Decreased use of broad-spectrum fungicides for
the control of late blight (Phytophthora infestans)


And a particularly unhelpful footnote:

This technical note summarises the limited knowledge available for the control of Alternaria spp. in GB.

Seeing as I garden organically, this is of no use whatsoever:

Many of the most effective, modern late blight fungicides, which contain the following active ingredients, have no measurable activity against
Alternaria spp.:
• Cyazofamid
• Fluopicolide
• Mandipropamid
• Propamocarb hydrochloride


This morning I have cut down all the foliage, put it in the green bin and the Council will take it away tomorrow.  Every leaf has been picked up, the secateurs disinfected and my clothes went in the washing machine. All I can do now is cross my fingers and pray that the spores did not make their way into the greenhouse where they could devastate this year's tomato crop before it even gets started :{





We're some way from the village allotments and I had hoped that our relatively isolated location would protect me from this sort of thing.  Maybe the tubers I purchased were infected? Lack of organisation early in the season meant I didn't get to order virus-free tubers from a reliable online source.  I bought some potatoes from a local store, and some from Wilko.  That'll teach me :{

Bit ticked off but hey, luckily we're not dependent upon the crop for a filling meal.  Apparently I need to leave the tubers a couple of weeks before harvesting them, so that's one job less to do before the weekend.  Another gardening lesson ... you never stop learning :}



4 comments:

  1. Blight will come some years whatever you do - although I doubt that your Wilko seed potatoes were infected. In my opinion, it's far better to take a chance on blight rather than buy blight resistant spuds (sarpo varieties) as they taste of sod all.

    Your best chance is to grow potatoes as early as you dare (fleece if necessary) and get the spuds up and out the ground as soon as they've had 12/14 wks. Conversely, now that you have a the blight spores around, keep the spuds safe underground for another month or two before you dig them up.

    Good luck with the tomatoes - my early-planting-early-cropping strategy means that I've not had potato blight at the Hill (when others have), but two years in a row of crushing disappointment when I lost every single tomato plant and masses of green fruit in 48hrs mean that I only grow tomatoes at home, and that seems to work for me.

    I believe that bordeaux mixture is certified as safe to use by the Soil Association, but without reading up on the subject, I may be wrong.

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  2. Hazel, wonderful comment, thank you for taking so much time.

    Warming the soil with fleece for early planting is excellent advice, unfortunately this year they went in on 10th April and it was exactly 12 weeks yesterday ... but they will be in a different part of the garden next year so fingers crossed.

    I understand leaving the spuds underground for a while but is that only if you're going to store them? I usually harvest about 5 minutes before they hit a pan of boiling water ...

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  3. Yes, with the mild winter and fleece to warm the soil and protect the haulms against lower temps as they grow, you could have got them in probably a month earlier than you did.

    You're right in that the plan is to keep the spores on the soil surface, and the potatoes tucked up underneath so that when you dig up the spuds to store they haven't passed through blight spores which will cause them to rot.

    But with your plan of digging up a plant-at-a-time to use immediately, you will have to be careful not to disturb the rest of the tubers in the soil in case you transfer blight down to those.

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    Replies
    1. Thanks Hazel, I've got a lot to learn about growing veggies!

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