Integrated Pest Management

IPM Manual for Landscape Pests in British Columbia

Chapter 4: IPM for Vegetation

Learning Objectives

When you have completed this lesson, you should be able to:

1. Classify common landscape sites into three categories according to maintenance level required for problem vegetation.
2. List ways to prevent weed problems in hard-surfaced sites and in planted beds.
3. Know where to look for help in identifying plants.
4. List six characteristics of plant populations that can be counted or measured in a monitoring program.
5. Give examples of vegetation treatment thresholds.
6. Describe physical and mechanical controls for vegetation.
7. List guidelines for selecting appropriate herbicides.
8. Describe the role of evaluation in an IPM program for vegetation.

Introduction

IPM for vegetation (also called integrated vegetation management or IVM) is an important area of pest management in BC landscapes, particularly in coastal areas where the climate favours plant growth nearly year-around. Vegetation management described in this chapter covers:

• areas where no plant growth is desirable, such as paved surfaces and sidewalks;
• areas where low-growing or minimal vegetation is acceptable, such as along fence lines and around lamp posts, and
• planted areas, where weeds occur among desirable plants in flower and shrub beds.

Problem vegetation is any plant in the wrong place. This includes herbaceous annuals, biennials, and perennials as well as woody plants and mosses. As described in Chapter 2, using a system for categorizing sites according to maintenance level can help in planning an IPM program.

Facility Categories

Examples of sites that might be included in each category include:

• Class A - High level of service: formal display beds, high traffic areas, cemeteries, playing courts, botanical gardens, city hall grounds, residential yards.
• Class B - Moderate level of service: boulevards and medians, general park and playground area, parking lot perimeters, sidewalks, perennial borders, residential backyards.
• Class C - Low level of service: utility areas, works yards, natural parks, low use recreational areas and trails, fence lines.

The following section describes steps in an IPM program for vegetation and gives examples of techniques currently available to vegetation managers. This information is intended as a starting point, to be adapted to specific sites and improved as new products and methods are developed.

Prevention

Designing facilities to prevent undesirable plants from becoming a problem is the key to long-term vegetation management. Sites can be designed or modified to eliminate "weed zones", which are trouble spots that are repeatedly filled by invading weeds.

Hard-surfaced Areas

Examples of design changes that can make a large difference in future weed problems include:

• Install a paved or mulched mow strip under fence lines to block weed growth and eliminate the need to use herbicides or trimmers.
• Extend asphalt surfaces, such as playing courts or parking lots, past the outside edge of fencing so there is no "weed zone" under the fence line proper.
• Install brick-patterned concrete or asphalt instead of using bricks or paving stones for sidewalks, driveway and other paved surfaces. This is most applicable in coastal areas of BC, where weeds growing in cracks is a serious problem; some municipalities have incorporated this design requirement into local building codes.
• Fill cracks in asphalt and concrete surfaces with a sealant to remove germination sites.

Planted Beds

Ways to avoid future weed problems at the design and construction stage of shrub beds, borders and other planted sites, include:

• Use weed-free nursery stock and bedding plants to prevent the importation of weed seeds.
• Prepare the soil to provide the best growing conditions for the desired plants so that they can out-compete weeds.
• Before planting new beds, deplete the seed bank in the soil. Do this by allowing weed seeds to germinate, then cultivate to kill the seedlings; repeat this 2-4 times, if possible.
• Apply organic or geotextile mulches to prevent weed from emerging or becoming established
  (see Chapter 3).
• Plant aggressive ground-covers and massed plantings that rapidly cover the soil surface and reduce the space, nutrients and light available to weeds.

Identification

Collect leaves or whole plants and identify them to species, if possible. Find out whether the plants are annuals or perennials, as well as other characteristics, such as whether they are grasses, broadleaf weeds, noxious weeds or woody plants. This information will help in deciding the best management methods and when to use them.

For plants that cannot be positively identified, collect leaf or flower samples or whole plants and press them, if possible, to preserve them for future diagnosis.

Identification resources include:

• reference books, plant guides (suggestions are listed at the end of this chapter)
• resources on the internet
• staff at garden centres, community colleges, botanical gardens
• professional diagnostic services

Note: Professional services and companies can send samples to the provincial Plant Diagnostic Laboratory, Ministry of Agriculture and Lands (there is a charge for this service).

Monitoring

Monitoring programs for vegetation are based on regular inspections. These can be simple visual inspections (rough estimations) to check for the presence of unwanted plants and their stage of growth. There are also characteristics of plant populations, however, that can be counted or measured to arrive at a more accurate estimate. This will be more useful than visual inspections in setting thresholds and assessing progress. Examples include:

Which Method: The choice of monitoring method depends on the site and the user. Once a method is chosen, the same one should be used each time so that counts and averages can be compared from one year to the next. For more information on the principles of sampling, see Chapter 1.

How Often: Frequency of monitoring depends on the category of the site, its history of weed problems and the local climate, as well as the budget. Most pest managers find 1-4 inspections per growing season sufficient for problem vegetation. On low maintenance sites, occasional visual inspections may be the only monitoring required. On high maintenance sites (i.e., Class A), the vegetation situation may be more accurately estimated by taking quantitative measurements.

Vegetation records should be kept for each major site. It is important to keep written records of all counts, as well as notes from visual inspections for future reference. Some managers also find it useful to take photographs for comparison from year to year.

Action Decisions

Given the large variety of sites and the many species of plants that may be a problem in landscapes, it is hard to generalize about injury and action levels. How much vegetation is tolerable depends on where the weeds are growing, the maintenance category of the facility and the consequences of leaving weeds untreated. Three main factors to consider in setting injury levels include:

a) Safety and security of site users, including:

• degree of trip or slip hazards from plants
• blocking sight-lines on roadways, parking lot exits
• concealment of signs, curbs or ditches by weeds

b) Potential for damage to structures and facilities, including:

• hard-surfaced sidewalks, playing courts and parking lots
• fence-lines, sign posts, culverts and ditch banks
• building foundations
• fire hazards

c) Aesthetic standards, which are affected by:

• visibility and use pattern of the site
• nature of the surrounding area (i.e., rural, urban, natural vegetation)
• nearby facilities that might be affected
• nearness to sensitive natural areas

It is important to develop written injury and action levels for major sites, particularly those requiring higher levels of service (i.e., Class A and B sites). This may take a few seasons to work out, using monitoring records and annual evaluations to fine-tune the levels. Where weed treatments are rarely used, as is often the case on low maintenance sites (i.e., Class C), developing action levels may be a low priority. In such sites, simpler criteria, such as degree of fire hazard or presence of noxious weeds might be suitable.

For any sites where herbicides use is being considered, decision levels should be quantitative (stated in terms of numbers or measurements). Examples of injury levels are:

• number of plants per linear metre of fence line or curb
• number of weeds per square metre of shrub bed or display border
• average height of vegetation around signs, guardrails, ditches or sight lines along roads
• number of plants of particular problem species (i.e., blackberry, Scotch broom, poplar) present on a site
• presence of any plants of a noxious weed species

For future reference and to help in later evaluation, write down the criteria used to set the injury and action levels. Although there may not appear to be much difference between injury and action levels for vegetation when herbicides are used, other types of treatments may have different action levels. For example, equipment that uses heat to kill vegetation is more effective on seedlings than established plants, therefore treatments could be timed to coincide with a flush of newly germinating weeds.

Treatments

Control of annual weeds should focus on preventing seeds from spreading and preventing dormant seeds in the soil from germinating. Controls for established perennials are usually most effective before the plants bloom, when nutrient reserves in the roots are at their lowest and the plant is least able to grow new leaves.

Remove weed seeds and organic material from cracks in hard surfaces, by regularly sweeping or flushing with water. Manually remove plants. Complete removal of roots is necessary for long term control of plants that resprout after cutting (for a weed pulling tool, see text box). Cultivate soil to kill weeds; use a tractor blade to scrape a gravel or sand surface to destroy weeds.

Chemical Controls

If chemical controls are necessary, the least toxic, effective herbicide should be used. Select the product according to the following guidelines. Make sure it is:

• effective and registered for the specific weed type
• applied as a spot treatment instead of broadcast application where possible
• applied at the right time to have the greatest effect on target plants
• does not have long-term residual effects if the area is to be planted later

Preferred Herbicides: Fatty acid herbicides are of low toxicity and are effective on annual weeds and some perennials (for more information, see Chapter 3).

Other Herbicides: There are two general types of herbicides: pre-emergent herbicides, which are applied to soil before weed seeds germinate, and post-emergent herbicides, which are used on plants in an actively growing stage, before seed heads form. Post-emergent herbicides can be divided into selective herbicides and non-selective herbicides.

• Selective herbicides affect some types of plants, but not others. For example, several herbicides kill broadleaf weeds, but do not affect grasses.
• Non-selective herbicides can kill any type of plant. They are used to control all vegetation in an area or as spot treatments on deep-rooted plants and those that spread by rhizomes, especially in sites where there is no desirable vegetation present.

First, the entire thicket must be mowed or cut down in May or early June to remove all woody top growth. The roots will sprout new shoots, which should be left to grow for the summer. In early September, treat the plants with the non-selective herbicide glyphosate. At that time of year, the herbicide is readily translocated to the roots. The plants may not appear to be affected for some time, however, they do not grow back in the spring.

Application Methods: The most target-specific application techniques available should be used where practical. This includes using back-pack or hand-held sprayers, low-volume closed-system applicators, and "wipe-on" applicators.

For more precautions and guidelines for using pesticides in landscapes, see Chapter 11.

Evaluation

After any type of treatment, the treated areas should be inspected for results at intervals appropriate to the type of treatment. For example, schedule an inspection 1-3 weeks after an herbicide treatment.

Use this information, along with other monitoring records, observations from field staff, feedback from clients, budget records, etc. to assess the effectiveness of the vegetation IPM program and find ways to improve it for next year. After several seasons of recording and evaluating, a long-term decrease in the vegetation problems should be noticeable.