Crabgrass is Everywhere

August 23, 2016

Many people have been calling and emailing us the past couple of weeks with questions over crabgrass (Digitaria spp.). If you have a light yellow green grass with wider blades than the rest of the turf, that seems to be growing at a much quicker pace than other parts of your yard, you more than likely have crabgrass.

Crabgrass with seed heads.

These plants germinated in the spring, but you didn’t notice them until recently probably. The good news is this grass is a summer annual and the growth will soon slow with the cooler temperatures and the plant will die after a killing frost. If a seed head forms on crabgrass, it can produce thousands of seeds on each plant, so your problem is already started for the next year.

Crabgrass can take over quickly.
Crabgrass quickly moves into areas where turf has been lost.

If you have crabgrass you have a few options:

  1. Since it is so late in the year it is best to just let the cool temperatures remove the crabgrass for you.
  2. Chemical controls exist, but at this stage in the plants development you will need to apply a couple of applications and it still may not kill the plant.
  3. Preemergence herbicides don’t help once the crabgrass has emerged.

Tips for preventing crabgrass:

  1. Fertilize your existing turf this fall. A healthy turf stand will have less weeds due to a more uniform canopy with few openings for crabgrass to move into.
  2. Seed thin spots in the next couple of weeks to help thicken the turfgrass you want.
  3. Maintain turf at 3-4” height of cut. Taller turfgrass stands tend to have less weed pressure since the leaves shade out the germinating crabgrass.
  4. Put out a preemergence herbicide by May 1st in central Iowa, since crabgrass germinates from seed each spring. Crabgrass will germinate once soil temperatures reach 55 degrees Fahrenheit.Try to time this application with a ½ inch rainfall or irrigation within 3-5 days of applying the preemergence herbicide.

Crabgrass is excellent as self seeding.
This area may need some additional grass seed after the first frost.



Adam Thoms Assistant Professor

Adam Thoms, Ph.D. - Assistant Professor specializing in Commercial Turfgrass Management, Iowa State University, Department of Horticulture, Ames, IA. Dr. Thoms received his B.S. from Iowa State University, and both his M.S. and Ph.D. in Plant Sciences and Plants, Soils, and Insec...