hello Sir
Potato blight (Phytophthora infestans)
Control:
Grow resistant varieties
Where blight is common, grow early bulking varieties that produce a reasonable crop before blight appears.
Earth up or mulch with a thick layer of leaves, straw or hay, to reduce tuber infection.
Once the disease has taken hold it cannot be cured.
To save the crop cut off and remove all foliage.
Wait three weeks before lifting the tubers so any lingering spores, that could infect the tubers as they are lifted, will have died.
Common scab (Streptomyces scabies)
Grow resistant varieties
Improve soil moisture holding.
Scab is much worse in alkaline conditions. Do not lime soil before planting potatoes.
Put a layer of grass mowings in the planting hole/ trench.
Water, if conditions are dry.