Lectures 1 and 2. Landscape weed Management Goals and Principles

Goals:

Primarily aesthetic -- maintain and improve the visual quality of the landscape

Functional: weeds can affect safety, health, allergies, insect and diseases

Poison ivy causes allergic dermititis; Sandbur can be a real pain in bare feet; and, ragweed pollen causes allergic "hay fever" in many.

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.

1. Woody tree & shrub beds ----------> Most post-plant weed management options

2. Woody groundcover beds

3. Annual beds

4. Perennial beds

5. 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.

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Table 1. Weed management options and limitations for the five types of landscape plantings.

Tree and Shrub Beds: Densely shaded plantings exclude weeds.
• -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.

Woody Ground Cover Beds: The ground cover should ultimately exclude most weeds
• -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.

Annual Flower Beds: A closed canopy will shade-out many weeds.
• 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.

Herbaceous Perennial Beds: Similar to Annual Flower Beds except:
• 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.

Mixed Plantings (of woody and herbaceous plants):
• 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.
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Step 4. Site Preparation:
Goal: eliminate weeds that cannot be controlled after planting
Options:
Cultivation
Non-selective herbicides
Fumigation (last resort with no other options are available)
Solarization

Step 5. Installation and implementation.

• Site preparation and sanitation.

• Mulches

• Preemergence herbicides

• Postemergence herbicides

Study Questions

1. What are the 5 types of landscape plantings?

2. List the types of landscape plantings in order from the most to least post-plant weed control options.

3. Give an example of how landscape plant selection can influence your weed management choices.

4. What are the key weed management option differences between the 5 landscape bed types?

5. Following a site assessment -- What is the key question you ask yourself (and answer) concerning the weeds present in a proposed landscape planting?