Blightwatch revisited

Good looking potato foliage and flowers

Once upon a time I wrote about potatoes and the excellent service called Blightwatch which warns when weather conditions become ripe for an outbreak of potato blight.

Back then the service looked out for a Smith Period i.e. a time during the potato/tomato crop season when the weather served up 90% humidity over an 11 hour period in temperatures above 10°C for 24 hours, and for both conditions to exist over a period of two days. If this occurred for my postcode area, then I'd get an email warning me that a Smith Period had happened, or one saying there was a near miss if the conditions only occurred for a day.

These emails usually started around July/August time and I always received them with a sense of impending doom.

Now since May this year I've had several emails called a Hutton Alert from the same service instead. This is much earlier to receive a blight warning and slightly worrying. Is my practise of growing early spuds to avoid late blight in danger now?

It seems the Smith criteria are no longer performing well, so the James Hutton Institute conducted some research to see if the system could be improved. All aspects of the criteria were tested and their results showed lowering the humidity factor to a mere six hours improved blight prediction significantly.

From what I've seen so far, it means pretty much any period of rain or damp weather results in a warning email and as a consequence I've become more blasé about the future health of my crop. I'm sure the farmers for whom this service is really designed take it much more seriously than I.

I do remember an incredibly early blight year a couple of years ago (in June) so I do have anecdotal evidence of the need for a different system, perhaps in response to a change in the way the blight fungus performs. However, my allotment is on a windy site, which I'm sure helps keep the blight at bay.

In the meantime, I'm watching my potato leaves for signs of an earlier blight than usual. All's well so far *crosses fingers*.

How's your potato crop faring this year? Do you subscribe to the Blightwatch alert system?


  1. An interesting, informative post. My potatoes have done well do far but I've yet to lift any as I'm waiting for the foliage to start dying back.
    I don't subscribe but keep an eye out when the weather heralds the possibility of blight. xx

    1. Thanks Flighty, I planted mine late, so I'm playing catch up!

  2. We do subscribe to Blightwatch but to be honest if you don't spray crops there is little you can do about it if you do get a warning other than to worry about it.

    1. Yes, back when I first posted bordeaux mixture was still available and garden organic said it was OK as a last resort. That's withdrawn from sale now and I was never sure I wanted to use it anyway. The service is more of use to those who do spray, such as farmers, but at least it gives a warning to keep a closer eye on crops so we can cut down the haulms asap if needed.


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