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herbicides and cultural practices can take care of weeds like this dandelion

Questions From The Plant Clinic: Pre-Emergent Herbicides in Lawns

This week in the Plant Clinic we had a question from a resident on what Pre-Emergent Herbicide he should use to take care of weeds in his lawns. Pre-emergent herbicides work by inhibiting the growth of seeds, keeping them from sprouting for a certain period of time. They must be applied before the seeds begin to sprout!

Can I get a recommendation on pre-emergent herbicides?

Which pre-emergent weed control you use is determined by what weeds you currently have in your lawn.  In the previous e-mails I don’t see what type of lawn you are growing, so I am going to assume it is St. Augustine. Healthy, well maintained turfgrass is its own weed control as it can out compete many different weeds.

If you have struggled with control in the past though, there are chemical options on top of proper cultural practices. According to the Weed Management Guide for Florida Lawns found on UF’s website [here], there are several different chemicals that can work as pre-emergent herbicides on St. Augustine. Pages 7 and 8 of that document list chemical names and examples of brand names to look for. The paragraph quoted below is the information on which chemicals work for which type of weed. I have bolded the chemical names so they are easier to find.

“In established turfgrass, members of the dinitroaniline herbicide family (e.g., oryzalin [Surflan], benefin and trifluralin [Team Pro], prodiamine [Barricade], or pendimethaline [Pendulum, Pre-M]) control annual grass and some broadleaf weed species when applied prior to weed seed germination.

Bensulide (Bensumec) and dithiopyr (Dimension) also provide preemergence annual grass and broadleaf control.

Atrazine and isoxaben (Gallery) primarily provide preemergence control of broadleaf weeds.

All these herbicides must be activated with irrigation or moderate rain within 2 days after application so they will be in direct contact with the germinating seeds and emerging weed seedlings. If the soil is dry, their weed-killing effect is greatly limited. On the other hand, if the turf is over irrigated, most pre-emergence herbicides will be moved below the soil layer where the germinating weed seeds are, reducing weed control.”

In that list above, the chemicals currently available to Home Owners are oryzalin (Surflan), benefin+trifluralin (Team Pro, Team 2G), pendimethalin (Pendulum, Pre-M, Halts Crabgrass Preventer), bensulide (Bensumec, Weedgrass Preventer), and Atrazine (many brands have this one).


Contact the Plant Clinic

The Seminole County Master Gardener Plant Clinic is open Monday – Friday from 9am-Noon and 1pm-4pm. For more information on how to contact a Master Gardener about your gardening questions, visit our website at this [LINK].

2 Comments on “Questions From The Plant Clinic: Pre-Emergent Herbicides in Lawns

  1. I live in South Florida, and I am wondering about a pre-emergent for our St Augustine in particular to prevent crab grass from seeding. Is there one that I can recommend to our professional chemical guy and one that I can use myself as a homeowner? If yes to both, when are the best times to put them down? I am a snow bird, and we always put pre-emergent down in March up north, but our lawn care professional in Boynton beach has never heard of a pre-emergent for St Augustine. Yikes! Hard to keep up is we are doing nothing preventative down here, I think.
    Many thanks!

    • Hi Sims!

      According to our UF/IFAS Website on crabgrass control, the time for pre-emergent application has already passed (back in February). They do have a list of both pre and post emergent herbicides to use on their website however.

      You can find the website at this link: https://edis.ifas.ufl.edu/ep395
      The easier to read PDF version of the website is at this link: https://edis.ifas.ufl.edu/pdffiles/EP/EP39500.pdf

      In order to remain unbiased, only the chemical names have been provided, with no trade names. You’ll have to look them up to see what brands are actually using those active ingredients.

      Let me know if you have further questions!

      Kaydie McCormick

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