Controlling weeds in turf

Thursday, April 5, 2012

Crabgrass Control -- There is always the urge to apply pre-emergence herbicides too early for crabgrass and other annual grasses. This is even more the case this year with the warm days that we've been experiencing.

Crabgrass germinates when soil temperatures reach and remain at 60F which usually occurs sometime in May. Pre-emergence herbicides only work when seeds are beginning to germinate and absorbing a lot of soil moisture. If the moisture contains pre-emergence herbicide, seedlings die.

For homeowners who apply products to their own lawns, the time to apply is the last week of April through mid-May. To prevent the need for a second application in June or reduce crabgrass problems later in summer -- "do-it-yourselfers" should apply pre-emergence herbicides at the correct time.

For professional applicators, the window of timing for application is expanded due to the number of lawns they treat. They would be unable to treat all contracted turf areas during the ideal application period. Observing professional applicators creates confusion. Homeowners should understand that professionals are applying different products with longer residual control and they have better equipment that can be accurately calibrated to apply products at the higher rates needed with earlier applications.

Pre-mergence Herbicide timing for crabgrass control is covered in an in-depth publication now available on the following UNL turf website. http://turf.unl.edu/pdfcaextpub/Crabgrasscontrolhomelawn2010b.pdf

Henbit, Speedwell and Blue Mustard -- are the purple and blue flowering weeds blooming now with blue mustard being the earliest to bloom. As winter annuals, most of the seed germinated last fall. The overwintering plants bloom in early spring, produce seed and die once hot weather arrives. Post-emergence herbicide applications are not very effective at this time. Hand-pull weeds if feasible. Determine why turfgrass is not competing with winter annuals and change cultural practices to promote grass density. Where herbicide control is needed, apply a pre-emergence herbicide in early September.

For more information on henbit and other winter annuals see the following UNL turf website. http://turf.unl.edu/ pdfctarticles/april%20pro%20winterannuals.pdf

Tall Fescue Injury -- Lawns seeded last fall might be showing winter injury from desiccation (drying) over winter because of our dry fall and fairly open winter. Bare areas may require reseeding this spring. Seed by May 15.

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