Just for fun I bought some lawn spray at Walmart, and then bought some from a gardening store. Of course Walmart was cheaper. But on closer inspection I found that the stock number for the Walmart product was exactly the same except for a suffix at the end of the stock number. It was "WMS". I contacted the company to inquire about the reason for the "WMS" on the Walmart item. The bottles looked exactly alike, same amount, same wording, everything. Everything except that "WMS". After some rather extended questioning, the representative finally admitted that the bottle with the "WMS" was a special run, just for Walmart. He would not admit to any differences, but I think most will be able to draw some conclusions as to why Walmart stuff is cheaper.