Herbicide Resistance Should Only Be Suspected When ....<BR> other causes of herbicide failure have been ruled out. <BR> <BR> the same herbicide or herbicides with the same mode of action have been used year after year. <BR> <BR> one weed that is normally controlled is not controlled while other weeds are. <BR> <BR> healthy weeds are mixed with controlled weeds (same species) <BR> <BR> a patch of uncontrolled weed is spreading. <BR>