NC State Extension

Lecture 9: Non-Selective Postemergence Weed Control in Landscapes

Go to Horticulture Information Leaflet (HIL-648), Postemergence, Non-Selective Herbicides for Landscapes and Nurseries.


Many formulations of glyphosate are currently on the market. Some of the common products include: Glyfos, Glyfomax, Glyflo, Target, and Touchdown Pro. They have the same active ingredient but inert ingredients differ. Specifically, the adjuvants included in the formulation are different. These differences are generally only evident in the rain-fastness and when you have hard water.

Roundup-Pro is rain-fast within about 2 hours whereas the generic formulations of glyphosate need 4 to 6 hours without rain or irrigation.

When mixed with hard water, the ions in the water bind with the glyphosate, essentially deactivating much of the herbicide. The result is reduced weed control. Roundup-Pro has an adjuvant that buffers the water and reduces the “deactivation”. Generic glyphosate formulations often suggest adding ammonium sulfate to the spray solution to improve performance in hard water.

If using pond water, it should be filtered to remove suspended clay particles which may bind with the glyphosate or glufosinate or diquat, thus reducing herbicide effectiveness.

Study Questions:

  1. Contrast systemic and contact.
  2. Compare and contrast the Scythe, Reward, Finale and Roundup-Pro. Aspects of comparison should include behavior in soil, contact vs systemic, relative effectiveness on annual and perennial weeds, how rapidly symptoms are expressed.
  3. What is the optimum timing (season or growth stage) of glyphosate applications on the following weeds: Johnsongrass, Bermudagrass, Mugwort, Catbriar (green briar), Japanese honeysuckle?
  4. In general, when is the best time to treat (with glyphosate):
    1. An herbaceous perennial that dies back to the ground in the fall.
    2. An evergreen woody weed.
    3. A deciduous woody weed.
    4. A perennial grass
  5. Describe three ways we “selectively” use non-selective herbicides such as glyphosate.
  6. What types of weeds will vinegar and flame weeders control?
  7. What types of weeds will they not control?
  8. How would you categorize hot-foam or steam weeders? Systemic or contact? Selective or non-selective.