Each time you place a Land F/X object (such as a block or hatch) or pipe to a piece of irrigation equipment, you see the Selection dialog box pictured to the right.
You have the Selection Cycling tool turned on. This tool can be handy in drawings that include a large number of overlapping objects. However, for your workflow as a landscape architect or irrigation designer, it's probably pretty tedious to have to close that dialog box repeatedly.
You can prevent this dialog box from popping up by turning the Selection Cycling tool off.
Type SelectionCycling in the Command line and press Enter. When prompted to enter a value, type 0 and press Enter.
Selection Cycling will be disabled, and you won't see the Selection dialog box anymore.