“Crabgrass” is sometimes used for any coarse-looking grass in a lawn. Start with a close photo showing the leaf, stem and growth habit. Correct identification separates an annual weed strategy from a problem that needs a different approach.
Understand the next generation
Maryland Extension describes crabgrass as a summer annual that reproduces primarily by seed. Thin turf and bare spots give it opportunities. Mark recurring edges and gaps so the long-term plan includes improving cover, rather than only responding to weeds each summer.
Coordinate prevention and repair
Preemergent products target germinating weeds; they are not a universal answer for mature plants. Timing should follow local conditions and the specific label. Many products also affect desired grass establishment, so plan overseeding and weed prevention together and check the required interval. A fixed national calendar date is not enough.
Keep the response proportional
A few identified young weeds may be manageable with a suitable hand tool. A widespread infestation calls for a broader review of mowing, turf density and the repair season. Before considering an herbicide, confirm the lawn species, target weed, permitted use and current label. Record what was applied so a later seeding decision is based on facts.
Do not assume the same herbicide fits every warm-season and cool-season lawn.