NC State Extension

Lecture 2: Principles & Tools

• Site Preparation
• Sanitation & Exclusion
• Mulches
• Preemergence Herbicides
• Postemergence Herbicides
• Hand weeding

Site Preparation

The best time to control perennial weeds is before planting.

There are basically three options: repeated cultivation, fumigation, or glyphosate (Roundup).

If the site is to be amended with topsoil or organic matter, inspect the sources of these materials for noxious weeds. Topsoil from farmland or stream banks is notorious as a source of nutsedge tubers and seeds of many annual weeds like morningglory and sicklepod. Inspect piles of compost or mulch for signs of weeds. Some species frequently found in mulch piles include mugwort, thistle, spurge, bindweed, and field horsetail. If these weeds are present, find an alternate source!

Cultivation.

Repeated cultivation on a regular schedule will control most weeds. Area will have to be left fallow for at least one full year possibly two. Generally not an option in landscape plantings.

Glyphosate (Roundup-Pro & others).

Nonselective, systemic herbicide that kills most weeds – shoots and roots. Note that even Roundup does not control all weeds. For species like nutsedge, Florida betony, field horsetail (Equisetum), and wild violet, fumigation may be necessary.

Site Preparation with Glyphosate (Roundup-Pro & Others)

• Timing is critical for perennial weed control. Some species are well controlled in the fall but not in the spring; and vice versa. (We will cover this in more detail later.)
• Understand what can be controlled and what cannot.

Fumigation is the option of last resort

Fumigants are very toxic, expensive and require significant site preparation.
If this is to be done — DO IT RIGHT!

Solarization

Using the sun’s energy to build heat in the soil; thereby killing weed seeds and vegetative propagules. Not as effective as Fumigation but simpler. Requires significant time and only effective in the summer. Even then, many perennial weeds will not be controlled. Not widely used.

Effectiveness of Pre-plant Weed Control Measures on Certain Hard-to-Kill Perennial Weeds

Species Roundup
Fall
Roundup Spring Fumigation Cultivation
Bindweed Good Poor Fair Poor
Japanese knotweed Good Poor Good Good
Mugwort Good Poor Fair Poor
Canada thistle Good Fair Good Fair
Wild Violet Poor Poor Good Good
Goldenrod Good Poor Good Good
Nutsedge Poor Poor Good Poor
Bamboo Poor Poor Good Good
Johsongrass Good Fair Good Poor
Bermudagrass Fair Fair Good Poor
Equisetum Poor Poor Fair Poor

Study Questions:

  1. What are the 3 main options for weed control at site preparation?
  2.  How do you know if fumigation is necessary?
  3.  If you have a landscape bed infested with crabgrass, henbit and other common annual weeds would you advise fumigation?
  4. Goldenrod is well controlled by cultivation. Why is this not a feasible option in landscape bed installation?
  5. Roundup (glyphosate) is non-selective. Under what situations would it not provide acceptable control for site preparation?

Written By

Photo of Brandon Hopper, N.C. Cooperative ExtensionBrandon HopperBusiness and Technology Application Technician (919) 515-3705 brandon_hopper@ncsu.eduHorticultural Science - NC State University
Page Last Updated: 2 years ago
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