Topic: smith periods - eek

[Multiveg]

Caernarfon has had 2 days of full smith criteria this month already  :( (though not consecutively so not a Smith Period  :-\ )

Smith Period conditions are conducive for sporulation of the potato blight pathogen on lesions - leaf wetness is also necessary for infection to occur. If Smith Periods occur at frequent and regular (7-10 day) intervals, there is a greater chance of blight development. This is because the generation time i.e. from original infection through to lesion development to subsequent sporulation is around 7-10 days. Smith Periods at these intervals would prove ideal for the blight pathogen.

http://www.potatocrop.com/blight/

[philcooper]

As I u nderstand it,Smith periods provide the ideal conditions for blight spores to do their worst, but you do need them present to start the spread in your area.

The disease tends to spread from the south west where the mild winters help it survive during the winter, then wind borne spores and aphids, whcih act as vectors, spread westward with the prevailing winds.

Local sources of blight can also occur, the overwintering volunteers being the worst offenders and that is the reason why they should be removed as soon as they are spotted.

Phil

[Multiveg]

Caernarfon is now in a Smith Period  :'(

[Ceri]

north east had a near miss a couple of weeks ago, but by the weather report, the north east may well be about to hit a full smith - today is day one of meeting the criteria - if it is the same tomorrow I think we'll be joining Caernarfon - and the weather forecast is not hopeful right now.  I'll be wandering around checking leaves tomorrow.

[Debs]

Seeing as I have never hear of this 'Smith period'  I would like to know what the signs and symtpms are...

Sounds like the Black Death for potatoes though... :'(

[philcooper]

As I said above, a Smith period in itself means nothing. It is, however a time, when, if blight spores are around, the disease will have ideal growing conditions. The time to get out with the copper spray to prevent the spores getting there little roots into the plant haulms is when blight is forecast in your area. For a fuller definition:

Smith Period Definition

A full Smith Period has occurred when:  
At least two consecutive days where min temperature is 10ºC or above and on each day at least 11 hours when the relative humidity is greater than 90%.  

A Near Miss occurs when:
One or both of the above two consecutive days has only 10 hours when the relative humidity is greater than 90%.  

Phil