Potato growers need to be on their guard for signs of stem blight as crops reach maturity. The British Potato Council (BPC) blight mapping programme (www.potato.org.uk/blight) reveals that in some areas there has been little spread of the disease, although inoculum levels are high and problems have flared up locally.
"Tuber blight is the sting in the tail that can catch out growers who drop their guard towards the end of the blight-spraying period," warns BPC's agronomist Mark Prentice.
"Stem infection can be difficult to spot, but produces a lot of spores, that can wash down to tubers. Meanwhile dry conditions have led to cracking on some soils, increasing the risk of spores washing down."
Although there have been few new blight outbreaks reported recently to the BPC website, there will be some areas of the country where blight risk will now be high, notes ADAS' Nick Bradshaw.
"There are reports from a number of areas of blight in crops at very low levels, and this year stem infections appear to be more common compared with leaf infections.
"Parts of the haulm such as the leaf axils are more likely to retain moisture in dry conditions. Any sporangia landing on these parts of the plant have a much better chance of surviving. Infection in these areas is more likely to lead to the development of stem lesions."
Stem lesions are closely linked to tuber infections, warns Mr Bradshaw. "The more forward maincrops have already bulked well and are approaching desiccation, while others are still some way off reaching market specification. In both situations, the blight control strategy must clearly focus on preventing tuber infection."
BPC advice is to remain vigilant, check the BPC website for local outbreaks, and match fungicide use to local blight risk. Spray choices should include tuber blight protection, advises Mr Prentice.
"Grower vigilance and tight spraying regimes have helped ensure incidences of blight have been relatively low this year. But all growers must keep up the pressure - there's no point in putting high risk crops in to store."