Many gardeners reach for a crabgrass-specific herbicide when they spot a clump of rough grass marring a smooth lawn, but not every grassy weed is crabgrass. Annual crabgrass (Digitaria sp.) and perennial tall fescue (Festuca arundinacea) require different treatments.
Crabgrass seeds germinate in spring and grow best in the heat of summer. The young clumps start out as upright blades before maturing into both vertical and horizontal tillers, or grassy offshoots. The blades grow 1/3 inch wide and up to 5 inches long. In late summer or early fall, long branching panicles appear before frost kills the annual.
Tall Fescue Identification
In contrast to crabgrass, tall fescue is a perennial cool-season grass. Cultivated varieties grow into tough, adaptable lawns, but the grassy weed is coarse and forms rough clumps. Tall fescue blades are larger than crabgrass blades, often growing nearly 1/2inch wide and up to 2 feet tall. Spiked flower heads appear in early summer.
Because crabgrass is an annual weed, pre-emergent herbicides that stop spring seed germination are the best defense. Tall fescue, on the other hand, survives winter cold and is more difficult to eradicate. Use a shovel to remove fescue clumps to a depth of 4 inches and re-seed the area, or spot-treat with a broad-spectrum herbicide.