Controlling Summer Annual Grassy Weeds in Lawns

crabgrass

Crabgrass

By Donn Meindertsma, Fairfax Master Gardener
As we enter the summer season, you might notice some new outlaws sauntering onto your lawn. Gone are the turf weeds of late winter and early spring, such as hairy bittercress and chickweed. A new crop is in town, the “summer annuals.” What are summer annual turfgrass weeds, and what can you do about them? This Article discusses some of the more common summer annual weeds found in our lawns that have a grass-like appearance, sometimes referred to as “annual grasses” or, as here, “grassy weeds.”

Summer annuals germinate in spring and grow until the first frost, completing their life cycle in one season. The self-seeding grassy weeds discussed here produce copious quantities of seed that, once dispersed, remain dormant in the soil in winter, ready to sprout when warm weather returns. While we might not ever be able to beat these formidable yard nuisances, we can control them.

Types of grassy weeds

Goosegrass

Goosegrass

Crabgrass (Digitaria sanguinalis, D. ischaemum) is readily distinguishable from desirable turfgrasses due to its scraggly growth habit and flat, relatively wide blades. It is a prolific self-seeder. Numerous sources accept the notion that one plant can produce up to 150,000 seeds per year. The seeds germinate, if exposed to light, when spring soil temperatures reach the mid-fifties. When summer temperatures arrive, crabgrass—as a warm season grass—is very competitive against the cool season, less-heat-tolerant turf grasses common in our region.

Crabgrass lookalikes include goosegrass (Eleusine indica). Goosegrass sprouts about a month later than crabgrass because its seeds require somewhat warmer temperatures for germination. If you successfully reined in your crabgrass early in the season, only to see it mysteriously reappear, you might in fact be looking at goosegrass. Goosegrass features a tight center rosette and silvery or whitish flattened sheaths. Viewed from above, it looks like spokes from a central hub.