Do you have a bright green, grassy weed in your lawn this month? It’s most likely annual bluegrass (Poa annua).
Annual bluegrass is a cool-season, annual weed that grows in compacted and moist soils.
It can even be found in shady locations. Sadly, annual bluegrass is a prolific seed producer with each plant producing over 350 seeds. Annual bluegrass is native to Europe and is found worldwide. Annual bluegrass has smooth leaves with a boat-shaped tip.
It produces greenish white seed heads throughout its life cycle, majority appearing during the spring months.
To keep this weed under control in your home lawn begins with irrigating the lawn properly.
Apply deep, but infrequent irrigation to the lawn during periods of inadequate rainfall.
Deep irrigation will encourage the turfgrass to grow a deeper, more vigorous root system. It will also help compete with the annual bluegrass for moisture. Wait until the lawn shows symptoms of drought stress before irrigating, especially in early fall. When the soil temperatures drop below 70F in the fall, annual bluegrass will begin to germinate. Limiting soil moisture near the soil surface reduces annual bluegrass’ germination rates.
Reducing soil compaction through core aeration is another cultural control method for annual blue grass.
Aeration should be performed early enough in the season so the turfgrass has completely recovered before annual bluegrass seeds begin to germinate in the fall.
Core aeration is best performed in early summer after the lawn has become fully green.
Raising the mowing height of the lawn during the fall will reduce annual bluegrass seed germination. Low mowing heights and scalping stress the turfgrass and limit its growth. Returning grass clippings to the soil when mowing is important to return nutrients to the soil and reduces fertilizer requirements. However, its recommended to bag the clippings when annual bluegrass is in flower. Bagging will help limit the spread of problematic seeds for next year.
Pre-emergence herbicides should be applied to well-established lawns in late summer or early fall when temperatures drop to a daytime high of 75 °F for four consecutive days. For most products, a second application needs to be applied 8 to 10 weeks later in the fall for continued control.
For more information on annual bluegrass or for an extensive list of recommended herbicides, please visit the Home and Garden Information Center website at
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