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  • Jared
    • Sep 3, 2020
    • 3 min read

So you have crabgrass... now what?

Updated: Oct 6, 2020

Whether you live in the north, transition or south, crabgrass can become a nuisance and without care, could ruin a beautiful lawn and landscape.


The Problem:


What is crabgrass?

Smooth crabgrass (Digitaria ischaemum) and large or hairy crabgrass (Digitaria sanguinalis) is a warm season annual grass that thrives under hot and moist conditions. Crabgrass is common for invading turf once soil temperatures reach 55°F. In the fall, crabgrass will slow its growth and die as soon as frost occurs.



What attributes to crabgrass growth:

  • Not applying a pre-emergent herbicide in late winter or spring prior to crabgrass germination

  • Hot weather causing drought resulting in thin turf

  • Thin turf due to less than optimal maintenance such as

  • 1) not applying fertilizer (or not enough) or,

  • 2) mowing grass too low

  • Thin turf due to insect and disease problems



The Solution:


What should I do now?

First, you want to find a selective herbicide that controls crabgrass, post-emergent. A selective herbicide is a type of herbicide that will only kill a certain type of plant, while leaving other plants unaffected. In this case, killing crabgrass without causing harm to your grass. Two common active ingredients that control and eliminate crabgrass are: quinclorac and mesotrione. Be sure to check the market label for specific information regarding these active ingredients, as other products on the market contain them, but at such small quantities that they won't control crabgrass.


What are some products that provide post-emergent control?


Which product is right for me?

Even though all of the products mentioned above are selective herbicides, not all of these are safe for all types of grass species. Prior to buying and applying any kind of herbicide, establish which type of grass, or all types of grass species, make up your lawn or application area.


All of the products listed above that contain quinclorac will harm fine fescue (if not part of a blend) and St. Augustinegrass. Prime Source (Select Source) Meso 4SC, which contains mesotrione, will harm Zoysiagrass and Bermudagrass.


Always reference the market label of the specific product to read the full list of restrictions, tolerant grass species and susceptible grass species.


What should I expect?

Prime Source (Select Source) Quinclorac 1.5 L: Crabgrass growth will stop after application and will start to yellow by the 3rd day following application. By the 10th day, crabgrass will be dead (pictured below). Expect similar results with BASF Drive XLR8 or Ike's Grass Weed Killer.


Quali-Pro Quinclorac 75 DF: Crabgrass growth will stop after application and will start to yellow by the 3rd day following application. By the 10th day, crabgrass will be dead (pictured below).


Prime Source (Select Source) Meso 4SC: Crabgrass growth will stop after application and start to turn white (due to loss of chlorophyll) after 5 days. Death may take between 2 and 3 weeks. A repeat application is required after 2 to 3 weeks for improved post-emergent control. Tolerant grass species may whiten temporarily after application.


What can I do in the future to help prevent this?

Apply a pre-emergent herbicide that prevents crabgrass in late winter, early spring or late spring depending on your location. Crabgrass begins to germinate when soil temperatures reach 55°F. Please reference our lawn care guide for specific regions (north, transition, and south) for an estimated time when a pre-emergent herbicide should be applied.


Sources:

  1. https://turf.purdue.edu/crabgrass/

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