Rough Bluegrass (Poa trivialis)

What it looks like

Patches of fine, soft, bright lime-green to yellow-green grass that stand out against the darker, coarser tall fescue. The leaf tip is boat-shaped like other bluegrasses, the underside of the blade is glossy, and there is a long, pointed membrane (ligule) where the blade meets the stem. It spreads by above-ground runners (stolons), so patches peel up like a mat. In July and August the patches thin out and turn brown, then green back up in fall.

Often mistaken for: Annual bluegrass (clumpy, seeds out in spring, dies in summer), creeping bentgrass, Kentucky bluegrass, or brown patch when it browns out in summer

When it shows up in the Triangle

Greens up early and is most obvious in March through May in the Triangle, then thins and browns out in summer heat and drought before returning in September.

Where you’ll see it

Shady, damp or over-watered parts of tall fescue lawns, often near downspouts, irrigation heads or under trees, and it usually arrives in a bag of contaminated seed.

What you can do

• Buy certified tall fescue seed with 0.00% other crop and weed seed on the label; this grass gets in through cheap seed
• Water deeply and less often; it thrives where the soil stays wet
• Reduce shade and improve drainage in the spots where it keeps showing up
• For small patches, dig out the mat plus an inch of soil and reseed in the fall
• Expect persistence: the stolons regrow from small pieces, so one round rarely finishes it