The bacteria causing scab is found in most soils - it’s usually the growing conditions which cause it to become a problem. Scab is reduced by irrigation and getting spuds up early also reduces damage.
Dry scab or also called common scab
Most severe in light soils in dry conditions . Dig in plenty of compost & do not lime before planting , try growing scab resistant varieties .
Powdery scab a darker colour than common scab & it becomes powdery when rubbed .
Severe in heavy wet soils , practice a five crop rotation system .
Add compost to the proposed site the previous winter . Plant without liming , try growing Estima or Pentland Crown which have a bit of resistance to it .
If you do have a soil test done it may indicate that the soil needs liming ,grow brassica on the limed ground in the next season .
Spuds & Animal dung based manures that have been three or more years of undergoing composting .
Use it once every five to seven years in late autumn , at the rate of one big barrow load per square yard , double dug in ,
Put your spuds on it in the spring , practice a five year crop rotation plan .
The spuds umbrella of leaves will choke off most weeds that grow through , pull out the really tall ones . The ridging also helps keep weeds down , run your rows North to South so they get even sunlight on each row side .