A full Smith Period has occurred when at least two consecutive days have had min temperatures of 10ºC or above and on each day at least 11 hours when the relative humidity has been 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% and the temperature is 10ºC or above. Of course, microclimates in the garden will also come into play and I find that going into the garden a couple of times a day to get a feel for the temperature and, more importantly, the humidity is a better guide to when conditions make blight more likely to occur.
|Full Smith Period alert for RG4|
Blightwatch.co.uk is run by the Potato Council's Fight Against Blight. To receive alerts of full Smith Periods you first have to register (free of charge) and then give it the first part of the postcode you want monitored. You can receive alerts by email or by SMS and view the charts online.
When it comes to treating plants, by the time the symptoms of blight have appeared it is usually too late to do anything. Most of the chemicals that have been used in the past to prevent blight have been withdrawn from sale to home gardeners in Europe but it has been suggested that aspirin may help protect plants (Trouble in the vegetable patch? Break out the aspirin). Prevention remains the best strategy. See Identify, prevent and treat Tomato Blight in the UK