If you have a trade name of Cascaded Landscaping INC.?

Question:and someone els has Cascaded landscaping WITHOUT the INC can they leagely sue you.

Answers:
Who had the company name first? Are you both located in the same vicinity? Did anyone register the name or get any type of trademarks on it?

Anyone can sue anyone else, business or otherwise, for anything they'd like. Whether they win or not is another question.