how do you rid lawns of worm casts

I dont know what effect the ferrous sulphate would have, possibly kill the worms which over time would cause damage to the soil strucutre and therefore lawn.
to get rid of the casts you can use a stiff brush/beesom to sweep the soi away. or collect it and use it as part of planting mixtures.

You shouldn't use any treatment on worms, they're good for the lawn. When they look unsightly, I just stamp them down!!

These are only a problem in autumn and spring, and a small price to pay for earthworm activity in the garden. Stiff brush when they're dry, collect up with a trowel or something when they're wet and put on the borders - they're full of good nutrients for plants.

Just to echo what bamboo said.

Yup totally agree with Bamboo and SBG!

Glad bamboo and I are on the same wormlength oops sorry wave length :o)

Looks like we're all on the same wormlength, Seaburng!

not one helpful comment so far i see where they are coming from,suphate is used by gardener for green lawns and getting rid of moss,i have read somewhere it also deters worms ,i know the products that kill worms have been taken off the market,but still widely used on golf courses,so those playing golf ,your game is slaughtering millions of worms.

I thought Seaburngirl's advice was very clear - take a stiff brush and sweep the casts off.

I thought we had answered the question of how to get rid of worm casts. as to how to stop them then you would have to kill the worms and that will in time be the 'death' of your lawn as there will be less air less nutrients etc.
sorry if my first comment wasnt helpful. if my humour in my later posts caused offense then I cant help my sense of humour, I have always enjoyed playing with the language. :o)

I knew there was a reason I didn't play golf...

Yup - me too! I go for a walk!