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Weeds: What's in Your Lawn?

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Weeds: What's in Your Lawn?

This winter, like most, seems to have been an ideal recipe for producing an abundance of winter annual weeds in cool season lawns throughout the Saint Louis area. As warmer days arrive these plants, which have been there all winter, will take off like weeds!

Winter annual weeds are one of our frequently encountered Common Garden Pests and Problems. They germinate in the fall and winter, grow actively in early spring, and complete their life cycle by early summer. Their life cycle ends after flowering and producing seeds for the next generation. The plants die and a new crop of weeds emerge from these seeds later in the year.

Both broadleaf and grassy winter annual weeds can be present in the landscape. So what’s in your lawn and landscape?

I know in mine, there’s an abundance of common chickweed (Stellaria media) and some annual bluegrass (Poa annua), pictured above. You probably have noticed lots of deadnettle (Lamium purpureum) and henbit (Lamium amplexicaule) in lawns, along roadsides and in fields throughout the area. Their pink/purple flowers are often rather beautiful, especially when they are not in your own lawn!

Winter annual weeds can either simply be tolerated in a lawn or controlled thru cultural methods and/or with the use of herbicides.

Culturally, a thick, healthy turf is much less susceptible to weed germination and establishment than a thin and weak stand of grass. Good maintenance practices such as proper mowing, fertilization, watering and aerification can all lead to a turf that is less favorable for weed growth.

Chemical control of winter annual weeds can be accomplished either with the use of a pre-emergent or post emergent herbicide.

Pre-emergence herbicides are those that are applied before the weeds come up. In the case of winter annual weeds, a pre-emergent herbicide would have to be applied in the fall prior to the germination of the weed.  One FAQ is which pre-emergent herbicide should I use? As a reminder, most of these products will also keep cool season grasses from germinating. Fall applications are best made on established turf. Applications may also be made to newly seeded grass that has germinated and been mowed at least 3 times.

Post emergence products are applied after the weeds are up and growing actively.  Winter annual broadleaved weeds could be controlled in the fall after germination and/or again in the early spring when growth resumes. For a listing of commonly used post emergent products follow this link to the pesticide page on Trimec.

A word of caution-in addition to the targeted weed, herbicides can also damage desirable plants. How do weed killers damage plants? The linked FAQ answer gives you much more information on the application and usage of these types of chemicals.

Need more information about winter annual weeds or other gardening information?  At the William T. Kemper Center for Home Gardening we can help. Just use this website, call in your questions to the Horticulture Answer Service (M-F from 9-Noon @ 314-577-5143) or ask your questions in person at the Plant Doctor Desk (Monday-Saturday from 10-3.)

Weeds: Take a look at what’s in your lawn!

Posted in: Spring | Tags: weeds , cool season lawns , St. Louis , winter annual weeds , chickweed (Stellaria media) , bluegrass (Poa annua) , deadnettle (Lamium purpureum) , henbit (Lamium amplexicaule) , herbicide , | Comments (0) | View Count: (3070)
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