How far does blight travel?

[Sylvan]

I've been growing tomatoes since 1985 and this year was the first time we had the dreaded blight.

Makes me wonder whether the reason we've never had it before was living in the middle of nowhere - miles away from other tomato growers, or living on cold windy hillsides.

[snohare]

Several years ago I remember reading that research had just been done which indicated that the upwellings of air that go up into thunderclouds, (which then turn into very powerful cooler downdrafts and sometimes tornadoes) have a dramatic and large effect on mixing all sorts of atmospheric ingredients, and can thus move bacteria, viruses and spores scores if not hundreds of miles. This was a bit of a blow to the traditional idea that barriers like the Channel can prevent the passage of pathogens. (Many will be killed by temperature and UV thankfully, but spores in particular may not be.)
So probably, if you didn't get it before, it was because there weren't enough nasties per cubic metre in the air, conditions locally weren't warm or humid enough or something similar, or perhaps more likely - maybe the spores are just more virulent nowadays because they have mutated into thousands of forms since the new strain arrived in the 70's. The latter might make it more likely to overcome less than ideal conditions for infection and reproduction.

[Sylvan]

Eek! I hope that doesn't mean we'll continue to get it, even if we move back to the boonies

[Aberdeenplotter]

Probably very likely likely that the blight spores have been present in previous years but the necessary temperature and humidity to trigger the disease has not been reached or maintained for long enough.

Strange names are used to define the necessary conditions:-

1. A Beaumont Period is a period of 48 consecutive hours, in at least 46 of which the hourly readings of temperature and relative humidity at a given place have not been less than 20 °C (68 °F) and 75%, respectively.

2. A Smith Period is at least two consecutive days where min temperature is 10 °C (50 °F) or above and on each day at least 11 hours when the relative humidity is greater than 90%.

[Sylvan]

That explains it then. Not many Smith Periods at 1500 feet - and even fewer Beaumont Periods!

Are both needed for blight to flourish?

[Aberdeenplotter]

yes, it's a combination.

[Thelma Sanders]

'Smith Period' was the result of reworking the 1950-1955 operations charts of A Beaumont (of the 'Beaumont Period', the classic UK potato late blight forecasting scheme published in 1947) to test the validity of using a shorter period of higher humidity. He found that 29 out of the 43 failures of Beaumont would have been valid using a 90% humidity criterion for 11 h in each of two days instead of the 75% for 48 h. Smith records that "The differences in effectiveness of the two systems, however, would appear to be small in practice and there would be little point in altering an established system unless the benefits are likely to be considerable". It was not until 1975 that the Smith period came into full operation and formed the basis of blight forecasting in the UK. It is still the most widely used forecasting scheme in the UK and has proved to be very robust. Topically, LP published a paper in Nature on an analysis of the foot and mouth disease outbreak of 1967, concluding that weather played a greater part in the spread of the disease than was previously recognised.

so they're nearly the same

(quote from BSPP News L P Smith obit)

[Sylvan]

Thank you

[snohare]

Subscribe to Blightwatch Sylvan, it is Smith Periods rather than Beaumonts, and for potatoes rather than tomatoes - but it will give you a heads-up for your postcode area even if it cannot predict with certainty whether or not it will strike you.

[Sylvan]

I started to snohare, but the trouble is my postcode area covers more than 30 miles, so I didn't think it would be much use.

[snohare]

30 miles ! Where are you - the Great Plains ? ! Wales ??

The secret there I'd say is to pick a postcode that is just below your area in altitude, and the same distance from the sea. When you get a warning for there, you will know that a little bit warmer where you are - if you are not already warm enough - and you will be at high risk.

[Sylvan]

North Pennines snohare

[snohare]

Oh, worse ! My condolences.

[binley100]

This year I've had two alerts about near misses.......my toms have all been fine and my tatties. However I've just had to pull out the selfsown toms in the CG cos they were showing signs . Luckily managed to rescue a lot of the fruit .

[Sylvan]

Good going though Binley. Mid-October.