Using Weeds as Indicators of Turf Management and Environmental Conditions

It is commonly thought that large weed populations are responsible for driving desirable grasses from a turf area. In reality, the presence of weeds, and the lack of turf, often indicates the turf's inability to compete and survive in settings where weeds can. Although it is impractical to expect totally weed-free turf, the presence of large numbers of weeds is often an indication of problems in the growing environment or in turfgrass culture. Employing recommended cultural techniques and altering the growing environment can improve turf quality and health and, thus, reduce the need for pesticide applications.

Reasons for weed invasion

Large populations of weeds in turf are usually indications of:

Weeds specific to certain environmental and management conditions

Often, the presence of specific weeds in turf provides clues to the type(s) of environmental and management problems. By learning about weeds that commonly occur under certain conditions, managers can more easily identify these problems and correct them. The following list groups weeds by the environment in which they often occur.

Acid Soils High-Fertility Soils
bentgrasses (Agrostis palustris) annual bluegrass (Poa annua)
red sorrel (Rumex acetosella) bentgrasses (Agrostis palustris)
  bermudagrass (Cynodon dactylon)
Compacted Soils crabgrasses (Digitaria spp.)
annual bluegrass (Poa annua) mallow (Malva neglecta)
common chickweed (Stellaria media) purslane(Portulaca oleracea)
goosegrass (Elusine indica)  
knotweed (Polygonum aviculare) Low Fertility
mouse-ear chickweed (Cerastium vulgatum) plantains (Plantago spp.)
prostrate spurge (Euphorbia supina) red sorrel (Rumex acetosella)
Dry Soil Low Mowing Height
black medic (Medicago lupulina) annual bluegrass (Poa annua)
red sorrel (Rumex acetosella) bentgrasses (Agrostis spp.)
  crabgrasses (Digitaria spp.)
Dry, Infertile Soils white clover (Trifolium repens)
yarrow (Achillea millefolium)  
  Moist Shade
Moist or Poorly Drained Soils annual bluegrass (Poa annua)
annual bluegrass (Poa annua) nimblewill (Muhlenbergia shreberi)
bentgrasses (Agrostis spp.) violets (Viola spp.)
common chickweed (Stellaria media)  
crabgrasses (Digitaria spp.) New Seedings
goosegrass (Elusine indica) crabgrasses (Digitaria spp.)
ground ivy (Glechoma hederacea) henbit (fall plantings) (Lamium amplexicaule)
mouse-ear chickweed (Cerastium vulgatum) purslane (Portulaca oleracea)
violets (Viola spp.) yellow foxtail (Setaria glauca; also listed as S. lutescens)
yellow nutsedge (Cyperus esculentus)  
Moist, Fertile Soils annual bluegrass (Poa annua)
curled dock (Rumex crispus) common chickweed (Stellaria media)
henbit (Lamium amplexicaule) ground ivy (Glechoma hederacea)
yellow woodsorrel (Oxalis stricta) mouse-ear chickweed (Cerastium vulgatum)
nimblewill (Muhlenbergia shreberi)
Moist, Infertile Soils violets (Viola spp.)
white clover (Trifolium repens)