Lecture 1: Goals & Principles
Primarily aesthetic — maintain and improve the visual quality of the landscape
Functional: weeds can affect safety, health, allergies, insect and diseases
Principles: 5-step process (Handout: Plan Before You Plant)
Recommended (strongly) reading:
Plan Before You Plant — A 5-Step Process for Developing a Landscape Weed Management Plan
Step 1. Site assessment
Key weeds – perennial broadleaves and sedges
Grassey weeds can be controlled postemergently with selective herbicides
Ask yourself the question: “Can I control these weeds after Planting?”
Step 2. Define the Planting: 5 Types of Landscape Plantings
The type of planting will define the post-plant weed management options and the importance of pre-plant weed control.
- Woody tree & shrub beds — Most post-plant weed management options
- Woody groundcover beds
- Annual beds
- Perennial beds
- Mixed planting — Fewest post-plant weed management options
Step 3. Selection of ornamental species and compatible weed management options.
Example 1: Florida betony cannot be selectively controlled in beds planted to herbaceous ornamentals. Therefore, opting for a woody planting instead will make maintenance easier by allowing the use of effective herbicides.
Example 2: Yellow nutsedge can be controlled with preemergence applications of Pennant Magnum in Ageratum or Petunia beds but not in Begonia or Coleus.
If yellow nutsedge has been a problem in the past – plant petunias instead of coleus.
Table 1. Weed management options and limitations for the five types of landscape plantings.
- Geotextiles and mulches are useful.
- Many broad-spectrum herbicides are available for pre- and postemergent control.
- Spot or directed applications of non-selective herbicides, like Roundup, are possible.
- Therefore: species selection is flexible and pre-plant weed control is not as critical.
Recommendations: Control perennial weeds before planting (although control may be possible after planting), use geotextiles with a shallow layer of mulch, use a preemergence herbicide if needed, and supplement with spot applications of postemergence herbicides and/or hand weeding.
- Limited uses for non-selective herbicides; therefore, control perennial weeds before planting
- Do not use geotextiles where ground covers are expected to root and spread.
- Control annual weeds with mulching, hand weeding, and/or herbicides.
- Several preemergent herbicides are available.
- Few uses for postemergence herbicides
- Postemergence control of annual and perennial grasses is possible.
Recommendations: Control perennial weeds before planting, use geotextiles where possible; else use mulches with a preemergence herbicide and supplement with hand weeding.
- Periodic cultivation (annually or between display rotations) will suppress many weeds.
- Very limited use of non-selective herbicides; control perennial weeds before planting.
- Geotextiles generally are not useful (due to the short-term nature of the planting)
- Few preemergent herbicides are safe; careful species and product selection are required.
- Mulches will suppress many annual weeds.
Recommendations: Control perennial weeds before planting, carefully select species for weed management compatibility, use mulches, a preemergence herbicide, and hand weeding.
- Lack of periodic cultivation will encourage perennial weed encroachment.
- Fewer herbicides are labeled; check the labels carefully.
- Geotextiles may useful in clump-type plantings or to restrict growth of spreading-types.
- Very limited use of non-selective or postemergence herbicides.
Recommendations: Control perennial weeds before planting, use geotextiles where possible, use mulches with a preemergence herbicide (where possible), and supplement with hand weeding.
- More complex due to the diversity of species.
- Different areas of the bed could receive different treatments.
- Site preparation is usually critical.
- Few herbicides are registered for a wide spectrum of ornamental plant types.
- Geotextiles may or may not be useful.
Recommendations: Maximize the number of weed control options by compatible species selection. Control perennial weeds before planting, use geotextiles where possible, use mulches with a preemergence herbicide where possible, and supplement with hand weeding.
Step 4. Site Preparation:
Goal: eliminate weeds that cannot be controlled after planting
Fumigation (last resort with no other options are available)
Step 5. Installation and implementation.
- Site preparation and sanitation.
- Preemergence herbicides
- Postemergence herbicides
- What are the 5 types of landscape plantings?
- List the types of landscape plantings in order from the most to least post-plant weed control options.
- Give an example of how landscape plant selection can influence your weed management choices.
- What are the key weed management option differences between the 5 landscape bed types?
- Following a site assessment — What is the key question you ask yourself (and answer) concerning the weeds present in a proposed landscape planting?