You could spray the weeds with a systemic weedkiller keeping the spray off the plants you want to keep. However, I would remove the offending plants by hand and either burn or compost them.
I have just found this forum hence the slow response to your question.
What you have found are worm casts on your lawn and are not caused by slugs. The casts are effectively worm poo, so rake them over to break them up and leave on the grass.
