If you notice pure white patches of grass in a lawn or spread throughout a lawn, these are likely weedy grasses sprayed with mesotrione. This herbicide is a chlorophyll inhibitor. It breaks down chlorophyll to prevent photosynthesis causing plants to die. A common brand is Tenacity.
At one time the only way to control weedy grasses in turfgrass was to dig them out or apply glyphosate (Roundup) to the weed, then reseed the area. This is referred to as nonselective control since glyphosate kills any plant it is applied to. Mesotrione provides selective control. Some weedy grasses are killed while some turfgrasses, like Kentucky bluegrass and tall fescue, are not usually harmed. Label directions must be followed to avoid injury to lawns.
Annual weedy grasses killed by mesotrione are crabgrass, goosegrass, yellow foxtail and others. As annuals, these weeds grow from seed each spring and summer then die after producing new seed. They do not overwinter as plants. The best way to manage annual weeds is maintaining a dense turf, using a tall mowing height, and applying preemergence herbicides in late April and May. If needed, mesotrione can be used for postemergence control after grassy weeds have emerged and are growing.
