Preen is successfully used to stop seed germination by many iris growers including myself without any problem. Late in the fall you might try trimming your DL's back and covering a few at a time as you spray the perennial weeds in that area with a mixture of Round-Up and Weed Be Gone. Use full strength Round-up mixed with a little water. Grass Be Gone has worked well in my garden on the difficult perennial grasses. Fall is a great time to spray as the plants will draw the spray down and kill the roots....our goal
