There is some crabgrass growing on the field and you may have noticed that it is turning white. This is a bleaching effect that comes from a chemical called Tenacity.  The active ingredient, mesotrione, is based on a naturally occurring compound produced by the bottlebrush plant (Callistemon citrinus) that inhibits photosynthesis in the crabgrass plant.  As you see the plant begin to turn white this shows that photosynthesis has been inhibited and the plant begins to die.  We have some Poa Anuua grass growing on our field as well among the perennial ryegrass.  The Poa tends to thrive in the shady and damp spots on the field while the perennial rye favors full sun.  With all of the extreme temperatures we experienced so far this summer, the grass plants have been under tremendous environmental stress and disease pressure.  Poa is susceptible to damage from Tenacity if it is stressed out already.  Therefore I did not spray for crabgrass for two weeks when stress levels were high (and we were losing some of the poa to disease already).  This allowed a window of opportunity for crabgrass to grow in certain areas on the field.  When stress conditions alleviated, I sprayed the crabgrasss immediately and what you are seeing now is the crabgrass plant dying.  The crabgrass will continue to die back and will be gone shortly.