So far this has been a lousy summer - at least here in N. Wales. Yet there have been very few reports of blight in potato crops in UK. So far, according to the Potato Council (now called AHDB Potatoes) website there is blight in 4 crops in Scotland, 4 in England and just 1 in Wales. Undoubtedly, there must be more than this as lots of outbreaks remain unreported.
What is clear is that the amount of blight reported is a whole lot less than in any other year recently. Usually, by this time, blight has been seen most areas of the country and some crops are severely infected. Why can this be?
We certainly have had lots of dry weather that does not suit the pathogen and this has been combined with cold nights. Blight does not multiply and spread in these conditions. However some districts have had Smith Periods (warm and moist), conducive to blight but the organism has not been around to take advantage and growers there have been lucky so far.
But we should not be complacent. We still have August and September left in the growing season and plenty of opportunity for blight to appear in force to cause havoc particularly in the maturing tubers. If the new potatoes get infected, they will not store and could start to rot soon after harvest. You can check on the incidence of blight in your area and the recent weather conditions here
A good method for controlling blight in a susceptible variety is to treat the crop with a liquid containing phosphite (phosphonate). A product like Phi-Diamond produced by Emerald Crop Science showed good control when we used it in 2013. It controlled foliage blight and treated crops gave a good yield advantage. Phosphite is thought to act by stimulating the natural resistance mechanisms in the potato and is a benign chemical compared with other biocidal chemicals and a whole lot safer to use than the heavy metal poison that is copper.