Weed Control in St. Augustinegrass: A Complete Strategy

Three Methods – Use All Three

1. Healthy Lawn: Vigorous grass resists weeds. Proper fertilizing, watering, mowing at correct height/frequency. Weeds invade bare/thin areas first.
2. Mechanical: Frequent mowing per guidelines limits weed development. Hand-pull annual weeds (effective, good exercise). Too time-consuming for perennials. Pull new/strange weeds immediately to prevent spread.
3. Chemical: Herbicides proven safe/effective. Must be applied at specific times for specific weeds. Many can't be used on all turfgrasses. Always read the label.

For a specific plan: know your turfgrass, know your weed, know your control options.

Weed Types

Broadleaf: Chickweed, henbit, dandelion, spurge, wild onion. Easy to spot – not grass. React differently to herbicides.

Grassy: Annual bluegrass, crabgrass, dallisgrass, bahiagrass. Harder to notice. Walk lawn regularly to recognize.

St. Augustine Weed Control: Two-Pronged

1. Prevent germination: Pre-emergent herbicides. Different chemicals/products for different seeds/longevity. Apply before germination. Summer weeds (crabgrass) → spring after 4 days of 60°F nights (forsythia bloom). Winter weeds (annual bluegrass) → early October. Water in after application.
2. Kill existing weeds: Post-emergent for grassy (goosegrass) or broadleaf (dandelions, onions). Apply when weeds actively growing (early summer).

Critical: Know weed name before using chemicals. Check label for weed control and turfgrass safety. Never exceed label rate – double dose can kill entire lawn.

Moss

Moss doesn't kill/crowd St. Augustine. Grows where St. Augustine can't (too shady/wet). Best control: change environment so soil dries faster (scrape moss, dig soil, plant fescue). Lime/moss chemicals = band-aid. Dry soil = no moss return.

Weed 'N' Feed Products

Generally apply one ingredient at wrong time. St. Augustine, zoysia, centipede: fertilize during/after green-up; pre-emergents before green-up. Fescue: "Weed 'N' Feed" with broadleaf killer OK in fall – but lawn must be damp for weed killer to cling.

Labels Are Not Decoration

Read label before buying. Ensure product does what you want on your grass. "If 1 tbsp good, 2 tbsp better" = FALSE. Overdose severely damages even tough grass.

Specific Weed Controls

Annual Bluegrass (Poa annua): Prolific reseeder. Attractive in winter, but April → thick mat chokes better turf. May → thousands of seeds/blade. Hot weather → dies, leaves bare spot + seeds. Best control: pre-emergent mid-September. If present in spring: non-selective herbicide (RoundUp, Roots & All, Finale) before seed forms. Mist foliage only. Alternative: wrap cotton towel on rake, dampen with RoundUp, "paint" weeds, avoid turf. Discard cloth in plastic bags.

Chickweed: Winter annual. Pre-emergent: isoxaben (Portrait). Post-emergent: 2,4-D + MCPP. Use on non-dormant grass (incl. fescue). Not on fall-seeded fescue until mowed 4×.

Wild Onions (wild garlic): Clumps ruin brown St. Augustine look. Reproduce by seeds + bulblets. Control: 2 sprays spring (6-week intervals) with non-selective (RoundUp, Finale) or broadleaf herbicide (Weed B Gon, Wipe Out). 2 sprays fall when foliage emerges. Imazaquin (Image) also works. DO NOT apply when turf emerging from dormancy. DO NOT apply to new/sprigged turf.

Nutsedge: Use imazaquin (Image).

Wild Violets: Difficult. Best = population management. Broadleaf killers (Weed 'B' Gon, Trimec) = fair. Spray 3× at 1-month intervals. Avoid spraying during green-up (wait until late April). Avoid drought – violets take up herbicide best when growing strongly.