What is causing brown patches in my lawn?
Lawn problems are read from the shape of the patch and from whether the grass is still rooted. Pull gently at the edge of a patch before anything else: turf that lifts like a carpet has lost its roots to a pest, and turf that stays put has a leaf disease.
The one observation that decides it
Pull, then measure. Turf peeling back with no roots, plus birds tearing at it, is leatherjackets. If it stays rooted, the pattern names it: coin-sized straw spots are dollar spot; irregular bleached patches with tiny coral-red threads binding the blades are red thread; a dark green ring or arc, sometimes with toadstools, is fairy ring; matted grey-brown patches with cobwebby growth appearing under or just after snow are snow mould.
Start from the plant in front of you
6 things it could be
Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.
Young plants cut clean through at soil level and left lying beside the stump. Later in the season, surface grazing on potato tubers and carrot shoulders. Scrape the soil within a few centimetres of a felled plant and a fat grey-brown caterpillar curls up in a C shape.
Conditions: 12–30°C · dry air ≤60%First move: Treat, then re-check in 5–7 daysSeen on: Sweetcorn
Yellowing, thinning patches of lawn that peel back like a carpet because the roots are gone. Birds — starlings, crows, magpies — tear the turf up in numbers, which is often the first thing noticed. Grey-brown, legless, tough-skinned grubs sit in the top 5 cm of soil.
Conditions: 5–22°C · humidity ≥80% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Lawn
Round patches 5–30 cm across of yellowed, then greyish-brown, matted grass. In damp mornings the edge of a patch carries white or pale pink cobwebby mycelium. Patches merge into large dead areas in a bad winter.
Conditions: -2–8°C · humidity ≥90% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Lawn
Small, sharply defined straw-coloured spots the size of a coin, which can merge into larger sunken areas. Individual blades carry a bleached lesion with a distinct reddish-brown border across the leaf.
Conditions: 15–30°C · humidity ≥85% · wet leaves / rainFirst move: Watch it before you actSeen on: Lawn
A ring or arc of unusually dark green, lush grass, often with a band of dead or thin turf just inside it, and sometimes a circle of toadstools after rain. The soil under a severe ring becomes water-repellent and the grass there dies of drought.
Conditions: 12–28°CFirst move: Watch it before you actSeen on: Lawn
Irregular bleached or pinkish patches from 5 to 30 cm across. Close up, tiny coral-red needles or threads bind the grass blades together at the tips — the feature that gives the disease its name.
Conditions: 15–25°C · humidity ≥85% · wet leaves / rainFirst move: Watch it before you actSeen on: Lawn