Heavy soils and those rich in organic matter are more likely to be ruined by worm activity. Try to remove grass clippings and other plant debris from the lawn and try to increase the acidity of the turf - annual top dressing with peat and the application of lawn sand containing sulphate of ammonia . Casts are most likely in Spring/autumn in mild damp weather. Try to disperse the casts by brushing out when dry before attempting to mow the lawn.
There is currently no chemical control registered for this problem.