Poa annua pre-emergent (late summer)
Annual meadow-grass germinates in late summer and early autumn. A pre-emergent applied in late August stops it before it establishes.
- When
- Aug 15 – Sep 10 (northern hemisphere) · Feb 15 – Mar 10 (southern)
- Material
- pre-emergent lawn herbicide authorised in your country
- For
- Cool-season lawns (ryegrass, fescue, bluegrass)
- Rule
- au-poa-preemergent · Turgeon
Annual meadow-grass (Poa annua) germinates in late summer/early autumn — a pre-emergent applied late August stops it before it establishes. ⚠️ Like all pre-emergents it blocks lawn seed too, so do NOT use it the same autumn you overseed; choose overseeding OR pre-emergent.
Why Poa annua is a problem
Annual meadow-grass (Poa annua) is a light green, clumpy grass that seeds prolifically, even at low mowing heights, and dies off in summer heat, leaving brown patches. It germinates mostly as soil cools in late summer and autumn, which is why prevention is timed then.
When
Mid-August to early September in a continental climate, as nights cool and soil temperature drops toward about 21 °C (70 °F) at 5 cm deep. Apply before the first flush of seedlings appears.
How
- Use a pre-emergent lawn herbicide authorized in your country, at the label rate, and water it in as directed.
- Do not scarify, aerate or rake hard afterwards; that breaks the barrier.
Overseeding or pre-emergent: choose one
Early autumn is also the best time to overseed. The pre-emergent stops grass seed too, so you cannot do both on the same area in the same autumn. If the lawn is thin, overseeding is usually the better long-term choice; a dense lawn leaves Poa little room.
Sources
- A.J. Turgeon — Turfgrass Managementturgeon