Signalgrass

Signalgrass is a warm-season grassy weed commonly found in lawns, pastures, roadsides, and disturbed soils throughout the southeastern United States. It grows aggressively in moist, fertile soils and can quickly form dense mats that crowd out desirable turfgrass species. Because it thrives under high humidity and warm temperatures, signalgrass can become a major problem during summer months.

How to Identify

Signalgrass is easily recognized by its broad, flat leaves and creeping growth habit. The stems often root at the nodes, forming low mats or patches. Leaves are smooth with a prominent midrib and a small membranous ligule at the base. The seedhead resembles a “signal” shape — with two to six finger-like branches radiating from the top of the stem, often giving the plant a zig-zag appearance when mature. Its seeds are small, oval, and dark brown.

Lifecycle

Signalgrass is a summer annual, germinating when soil temperatures rise above 65°F in spring. Growth is rapid through the summer, especially under warm and moist conditions. It reproduces solely by seed, and a single plant can produce thousands of seeds that persist in soil for years. Plants typically die after the first frost, but seedbanks allow rapid re-emergence the following season.

Prevention & Control

Control is best achieved through a combination of cultural and chemical methods. Maintain dense, healthy turfgrass to shade the soil and prevent seed germination. Mow at the upper range of recommended height to reduce light penetration. Pre-emergent herbicides applied in spring (before soil temperatures reach 65°F) can significantly reduce germination. For established plants, post-emergent grass herbicides labeled for signalgrass control are effective if applied while plants are young and actively growing. Repeated applications may be required.