Large crabgrass
Digitaria sanguinalis
Summer annual.
Grows up to 2 ft. tall; decumbent growth habit; swollen nodes. may root at nodes. Dies after the first frost in the fall.
By seed. Seeds germinate from spring through late summer.
Mowing the lawn too short. Thin turf with bare spots.
Mowed crabgass
Rainfall or irrigation is required to dissolve the herbicide which is then absorbed into the upper portion of the soil and forms a barrier which kills weed seedlings. Preemergent grass herbicides have residual activity that lasts for several weeks after application. High temperatures and rainfall will decrease the length of time they remain at sufficient concentration to be effective.
Tips for application
If it is growing it can be spot treated with a postemergent herbicide before it matures and goes to seed. Look for the following active ingredients.
Common Name: Quinclorac; Trade Name: Drive; others, can be combined with other active ingredients, Common Name: Fenoxaprop-p-ethyl; Trade Name: Acclaim Extra, others.
Publication: (PDF) TT43-Herbicides for Crabgrass and Goosegrass Control in Turf