In Indiana, you can spray crabgrass with a post-emergent herbicide anytime after the grass germinates until the middle of July. Crabgrass is too big to kill effectively in the mid to late summer, and the plant will soon be killed by cold temperatures.
About this Author
Melody Lee worked as a newspaper reporter, copywriter and editor for 5 years. In addition, she has edited magazine articles and books. Lee holds a degree in landscape design and is a Florida master gardener. She has more than 25 years of gardening experience, which includes working at nurseries and greenhouses.