The strains of blight that potato growers face in protecting their crops are becoming ever more aggressive, as only the fittest survive.
A good example is the recent strain 36A2. It is very capable of taking a crop down quickly, and even managed it in the heat of the 2018 summer. All it needs is some leaf wetness. Blight can change very rapidly, meaning these robust new strains are appearing in the wider population on a frequent basis.
For this reason most growers employ a suitably rigorous spray programme to keep this ever-increasing threat at bay. But they may be overlooking weak links created by poor cultural control, with potato dumps, volunteers and cover crops all potentially harbouring the water mould.
Site, variety and weather are all key factors which could potentially undermine a good spray programme.
Volunteer potatoes are incredibly capable of surviving all manner of things, such as cultivations, disease, frost, wet and herbicides. Volunteer potatoes must be treated as high risk as they may start an infection within the crop. They also host other things such as rhizoctonia, black dot and virus, so getting rid of them is a high priority.
Another aspect of cultural control which is frequently overlooked is that of volunteers in the autumn pre-cropping, as these are a potential time-bomb. If volunteers are left uncontrolled, they will normally become infected with blight.
This autumn will be the last for diquat use in potato crops, and this brings another challenge for growers. With existing alternatives to diquat, burn down will be slower and this will make things tricky at the tail end of the season.