IPM Prescriptions for Terrestrial Weeds
and Other Common Urban Vegetation Management Situations

Following are general IPM prescriptions for some common "urban" situations where "weeds" are typically a problem. Types of sites include planting beds; ornamental turf; around the base of trees, signs, fences, and other features in and adjacent to turf areas; gravelled areas; hard-surfaced areas; street and sidewalk joints and cracks.

Perennial Weeds in Planting Beds

Rhizomatous weeds are some of the most difficult to control weeds with non-chemical measures because, once established, their extensive network of rhizomes is impractical to remove and even tiny fragments of rhizomes left in the soil after manual or mechanical treatments will regeneration quickly. The weed problem that develops can often be more extensive before treatments were applied.

Target/Host
Planting beds.

Symptoms/Typical Damage
If allowed to become established, perennial weeds will spread quickly, creating conditions that are aesthetically unacceptable and potentially damaging to horticultural plantings due to competition for water, nutrients, and sunlight.

Potential Natural Controls

"Forces of Nature"

The natural environment (site, climate) may combine to create conditions unfavorable for the development of perennial weeds. Also, competition from desirable vegetation, planted or natural, may suppress weeds.

Cultural Management

Healthy, vigorous, and dense ornamental plantings are better able to minimize and withstand weed competition. Avoid deep cultivation of the soil when possible to prevent bringing the seeds already in the soil to the surface, encouraging their germination.

Habitat Modification

Reduce access to sunlight, moisture, and/or nutrients, using, for example: application of a spunbonded weed control fabric in combination with mulch; application of mulch only; denser planting of shrubs; and in some cases, groundcovers (see notes below about the use of mulches and ground covers and their effectiveness for weed control); utilization of drip irrigation rather than overhead sprinkler irrigation to manage availability of water.

Notes:

1. Often used for weed control, mulches can be much more effective if used in combination with weed control fabrics. This is especially true with fine mulches, like "bark dust", which are an optimum growing medium for developing weeds. Almost any mulch however, applied at an adequate depth, will provide weed control benefits. (See "Physical" below for further information.)
2. Although healthy, densely growing ground covers can be effective at competing against weeds, they do not exclude weeds entirely. In the case of noxious rhizomatous and stoloniferous weeds (e.g., quackgrass, horsetail, Canada thistle), once established, they are very difficult to remove manually, and in some cases even with the use of herbicides. In any case, damage to the groundcover is likely.

Design and Construction

Where shrub beds are designed to have an open ground surface, utilize spunbonded weed control fabrics or their equivalent, in conjunction with a mulch. (See "Habitat Modification" and "Physical" in this prescription.)

Incorporate physical barriers (e.g., mowing strip, heavy metal strip set on edge) at shrub bed/turf interface to prevent turf and turf weeds from encroaching into planted beds.

Design plantings so that they will quickly become dense and limit favorable conditions for weed development.

Where appropriate, utilize informal and/or naturalistic planting design rather than formal planting design. This makes a few weeds much less noticeable, and therefore more aesthetically acceptable.

When built-in irrigation is provided, utilize drip or micro irrigation systems and techniques in favor of broadcast irrigation systems.

When developing design specifications, do not allow new installations on weed-infested sites before control is established. This may require repeated cycles of cultivation/irrigation/weed germination/cultivation, and/or spot application of systemic post-emergent herbicide). Use high quality soil containing as few weed seeds, rhizomes, and other reproductive plant parts as possible. When it is expected that weeds will appear following landscape installation, develop a monitoring and treatment schedule that will provide for effective control when weeds are small. When possible, wash all equipment used in development projects prior to start of work to help prevent importation of weeds. Oversight and inspect landscape installations to ensure compliance with specifications.

Manual

Removal of the entire plant is necessary and, in the case of rhizomatous weeds, is only practical for new seedlings. However, removal of above-ground plant parts will prevent seeds from developing and may help reduce thriftiness of the existing weeds. Because rhizomatous weeds have the ability to reproduce new plants from very small fragments left in the soil, manual removal treatments can exacerbate some weed problems.

Mechanical

Power trimming of weedy areas can be used to prevent seed development and reduce plant vigor. Usually this method is considered a temporary treatment to keep weeds in check until a more effective option can be implemented.

Physical

Spunbonded weed control fabrics in combination with mulch can be used effectively where shrub beds have an open ground surface. Weed roots cannot reach the soil for moisture and nutrients or to become established in the ground (this is especially important with rhizomatous and taprooted weeds).

Where fabrics are not used, application of relatively coarse mulch containing little or no "fines" to a depth of 5-10 cm will help control weeds but must be supplemented by other treatments to provide effective results. If perennial weeds become established, control becomes more difficult and the use of herbicides may be necessary.

Chemical

When deemed necessary and appropriate, systemic post-emergent herbicides (e.g., glyphosate) can be used to effectively control established perennial weeds. Timely spot treatment of young perennial weeds before they become widely established and cutting of dense stands before treatment will help minimize applications. Fatty acid-based contact herbicides (e.g., Topgun) have shown effectiveness (on hot, sunny days) in killing some newly emerged weed seedlings. This product is not applicable to control of established perennials.

Pre-emergent herbicides are also an effective chemical tool but not one viewed by IPM philosophy as an acceptable routine methodology because they are almost always applied in a prophylactic and broadcast manner. However, it is important to note that there are instances where pre-emergent herbicides may be the only cost-effective option. (e.g., during site rehabilitation where: 1.) serious weed problems have existed, 2.) an extensive seed bank is present in the soil, and 3.) preventive long-term control options such as weed control fabric are not feasible).

Annual & Biennial Weeds in Planting Beds

Target/Host
Planting beds.

Symptoms/Typical Damage
If seeding is allowed annual and biennial weeds occupy large areas, develop a large "seed bank" in the soil, become aesthetically unacceptable, and compete against horticultural plantings for water, nutrients, and sunlight.

Potential Natural Controls

"Forces of Nature"

The natural environment (site, climate) may combine to create conditions unfavorable for the development of perennial weeds. Also, competition from desirable vegetation, planted or natural, may suppress weeds.

Potential Indirect Treatment Strategies

Cultural Management

Healthy and vigorous ornamental plantings are better able to prevent and withstand weed competition. Avoid deep cultivation of the soil when possible to prevent bringing weed seeds to the surface where they can germinate.

Habitat Modification

See "Habitat Modification" in prescription for perennial weeds above.

Design and Construction

Where shrub beds are designed to have an open ground surface, use weed control fabrics (e.g., spunbonded polypropylene or polyester) in conjunction with a mulch.

Design plantings so that they will quickly become dense and limit favorable conditions for weed development. Where appropriate, utilize informal and/or naturalistic planting design rather than formal planting design to help reduce the visibility of weeds and promote their tolerance as a natural part of the landscape.

When developing design specifications, do not allow new installations on weed-infested sites before control is established. This may require repeated cycles of cultivation/irrigation/weed germination/cultivation, and/or spot application of systemic post-emergent herbicide). Use high quality soil containing as few weed seeds, rhizomes, and other reproductive plant parts as possible. When it is expected that weeds will appear following landscape installation, develop a monitoring and treatment schedule that will provide for effective control when weeds are small. When possible, have all equipment washed prior to the start-work of development projects to help prevent importation of weeds.

Provide adequate oversight and inspection of landscape installations to ensure compliance with all contract documents.

Manual

Manual pulling and cultivation can be very successful and efficient in limiting annual and biennial weeds where populations are not extensive, providing this occurs prior to seed ripening. These weeds are typically very easy to pull and removal of the entire root system is not necessary although it is important to ensure removal of the root collar.

Mechanical

Power trimming of weedy areas can be used to prevent seed development and reduce plant vigor. Usually this method is considered a temporary treatment to keep weeds in check until a more effective option can be implemented. When new shrub beds are being installed or existing shrub beds renovated where landscape fabric cannot not be utilized, it may be is helpful to cultivate the soil, irrigate, wait for germination of weeds, and repeat several times. This treatment helps reduce the amount of weeds that are initiated from the "seed bank" in the soil.

Physical

Spunbonded weed control fabrics in combination with mulch can be used effectively where shrub beds have an open ground surface. Weed roots cannot reach the soil for moisture and nutrients or become established in the ground.

Where fabrics are not used, application of relatively coarse mulch containing little or no "fines" to a depth of 5-10 cm will help control weeds but must be supplemented by other treatments to provide effective results. If perennial weeds become established, control becomes more difficult and the use of herbicides may become necessary.

Chemical

Where manual or mechanical control are not feasible for established annual and biennial weeds, systemic post-emergent herbicides (e.g., glyphosate) can be used to spot treat offending plants. To minimize the volume of herbicide used, first cut the weeds and allow allow them to resume growing, then apply the herbicide. Fatty acid-based contact herbicides (e.g., Topgun) have been effective against some weed seedlings (on hot, sunny days) This product is not applicable to control of established weeds.

Broadleaf Weeds in Turf

Target/Host
Sports fields and general turf areas.

Symptoms/Typical Damage
These weeds can effectively displace turfgrass to the extent they adversely impact aesthetic quality and playability. With severe infestations, safety is a factor since weeds can form clumps that present a tripping hazard.

Potential Indirect Treatment Strategies

Cultural Management

Weed problems in lawns are indicative of site and/or cultural conditions that stress the turfgrass yet are favorable for the weeds. A strong cultural program is essential in maintaining healthy turfgrass, which in turn is capable of competing effectively against broadleaf weeds.

A cultural program for turf includes: proper mowing height, irrigation, fertilization, aeration (core aerating is considered preferable by many turf experts today), overseeding, and topdressing.

Mowing height is a critical factor influencing broadleaf weed growth in turf. Research has indicated that if a lawn is cut at 3.5 cm, dandelions can occupy 50% of the area, while a 6.5 cm mowing height keeps it down to an average of 1% under otherwise favorable conditions.

Various turfgrass species have different optimum mowing heights. Generally, a mowing height of 6 cm is commonly recommended for general purpose turf areas in parks with perennial rye and turf-type tall fescues; on sports fields, the tallest mowing height that is conducive to the particular species and will not interfere with play is recommended.

Summer irrigation is also a major factor in minimizing broadleaf infestations. Unirrigated turf is placed under stress for much of the summer in the Pacific coastal region, predisposing it to invasion by opportunistic weeds that are capable of developing under dry, compacted conditions.

Habitat Modification

Broadleaf weed habitat is minimized by soil conditions that are favorable for turf. These conditions can be developed or augmented through a routine cultural program.

Design and Construction

Construction specifications should state that soil imported for turf establishment be of the best quality possible.

When selecting grass seed mixes, match species and cultivars to site and use conditions and choose those that have been bred for disease resistance, drought tolerance, slower growth rates, etc. to minimize cultural requirements.

The use of "ecology lawn mixes", wildflower and/or grass meadows, and other alternatives to common turf mixes may be appropriate for some general turf areas, especially in low to medium maintenance zones. Ecology lawn mixes include attractive and compatible broadleaf plants (e.g. yarrow, chamomile, clovers, English daisy) in addition to selected turfgrasses; they have shown considerable promise for use as an alternative to turf. Ecology lawn mixes are designed to closely resemble turf in appearance and function but require mowing only every few weeks.

Wildflower plantings or 'meadow management' is also an alternative to maintenance of large, mostly unused turf areas.

However, while these features can be attractive and help reduce weed control requirements, wildflower plantings can be displaced by weeds and become unsightly. It is important to select species carefully and provide timely and effective control of invasive, domineering weeds. Experimentation with species and varieties as well as the timing and extent of weed control is necessary to develop an effective wildflower program.

Manual

Manual removal can be an effective method for controlling weeds in turf but is usually too time consuming to be feasible. When maintenance personnel are on-site regularly, manual control may be cost-effective for small, ornamental lawns.

Chemical

Chemical weed control treatments are seldom necessary on a wide scale when cultural maintenance is performed regularly. On ornamental turf areas where weed tolerance thresholds must be low, spot treatments with a post-emergent herbicide may be needed when soil conditions are poor and cultural treatments cannot be adequately applied. Because lack of irrigation can create significant stress on turf and provide an opportunity for weeds to become dominant,. to the extent feasible, irrigation should be provided for areas where high quality turf is considered necessary but chemical use is not acceptable. Regular, broadcast treatments of herbicides are not acceptable in an IPM program under almost any circumstances; all such uses should be limited to special or emergency conditions on a case by case basis.

Vegetation Growing Around the Base of Trees, Signs, Fences, and Other Features In and Adjacent to Turf Areas

Target/Host
Trees, signs, and other features in and adjacent to turf areas.

Symptoms/Typical Damage
Turfgrass growing around the base of features on or adjacent to turf must be trimmed to provide a neat appearance. When performed around the base of trees, damage can occur to the bark and lower limbs, sometimes seriously reducing the health and vigor of the tree, inviting secondary pest problems, and diminishing its aesthetic value. Other features may become scratched or otherwise damaged by trimming work.

Potential Indirect Treatment Strategies

Cultural

Raise tolerance levels for tall grass and weeds around objects in turf areas and maximize the interval between trimmings. Acceptable heights will vary with the feature and its prominence and importance in the landscape. With single trees, the best visual impact for this strategy can be achieved by leaving a wider unmowed area around the base of the tree. Where groups of trees exist, leave the turf within the entire area unmowed until trimming is necessary.

Habitat Modification

Install tree wells for single trees and/or other objects on turf areas (using a weed control fabric and mulch). Small groups of trees can also be mulched with landscape fabric underneath. Concrete underlayment and mowing strips may be added under or around fences, picnic tables, benches, etc.

Design and Construction

Avoid placing objects in turf areas; many features can be incorporated inside shrub beds, sidewalks, mowing strips, parking areas, etc. Space trees and other features within a turf area so that mowing equipment is able to get between them.

Include tree wells around single or grouped trees trees. Where possible, mulched areas should include a weed barrier.

Weed control fabric should be included with all tree wells. Without fabric, weeds established in the mulch require routine application of intensive labor or spot treatment with herbicides. Weeds developing in mulch on landscape fabric are easy to remove by hand, with or without hand tools.

Incorporate underlayment and mowing strips with fences, picnic tables, benches, and any other objects in turf.

Manual

Not practical on a large scale.

Mechanical

Hand held trimmers are necessary in situations where mowers are not able to cut all of the grass. Reciprocating trimmers are reported to be effective for removing grass around trees without causing damage to the trunk.

Chemical

New turf growth regulators (e.g., Primo) show promise in their potential for application around trees and other objects in turf. The manufacturer claims growth rates are reduced by up to 50% while turf rooting and color are improved. Reportedly, the product is low in toxicity and residual materials degrade into carbon dioxide and water).

The use of herbicides for routine suppression of vegetation around objects in turf areas is not a preferred option in the context of an IPM program.

Weeds in Gravelled Areas

Target/Host
Open areas, fencelines, bleachers, and other features located in and adjacent to gravelled areas.

Symptoms/Typical Damage
Weeds growing in gravelled cause a loss of aesthetic quality.

Potential Indirect Treatment Strategies

Habitat Modification

Concrete underlayment prevents weeds from growing underneath and around fencelines, bleachers, and other features. Turf may be used alternatively in some areas to improve aesthetic appearances but this option does not reduce overall maintenance requirements. Installation of pavement eliminates weed habitat altogether except where cracks and joints exist. These can be filled with a crack sealant.

Design and Construction

Incorporate underlayment where fences, picnic tables, bleachers, and other objects are located in gravelled areas.

Consider the use of spunbonded geotextile fabrics installed underneath a relatively shallow layer of gravel (i.e., 7-10 cm) to prevent weeds from rooting into the underlying soil, making them less thrifty and much easier to remove. The fabric also helps prevent the gravel from mixing into the subgrade.

Consider using paving materials rather than gravel, especially in high profile areas.

Manual

Hand pulling and manual cultivation can be cost-effective where weeds are few and easy to remove. Where more extensive problems exist and weeds are difficult to remove, this method is not feasible.

Mechanical

Hand held trimmers are effective and and may be efficient, depending on the types and amounts of weeds being controlled.

Tractor-mounted grading implements (e.g., ComboPlane, Turfterra) may be cost-effective in large gravelled areas.

Physical

Infrared/heat radiation, flamers, and hot water/steam. (See prescription for Weeds in Hard-Surfaced Areas for a discussion of these technologies.)

Chemical

Spot treatments with a post-emergent herbicide are effective.

Weeds in Hard-Surfaced Areas

Target/Host
Sidewalks, playgrounds, parking lots, lacrosse boxes, and other areas with pavement or interlocking pavers.

Symptoms/Typical Damage
Weeds germinate and grow in cracks and joints.

Potential Indirect Treatment Strategies

Cultural Management

Prevent weeds in surrounding areas from producing seeds to help prevent their migration to pavement cracks and joints.

Habitat Modification

Clean and seal cracks and joints in asphalt and concrete. Periodically reseal as needed to prevent the development of openings where weeds can develop.

Design and Construction

Limit the use of small, open-seamed pavers in favor of alternative materials where feasible and acceptable within appropriate design and planning criteria. Such materials include imprinted/colored concrete (e.g., Bomanite), exposed aggregate concrete, mortared bricks, larger paving units, mortared stone, etc. Also, research materials/methods for sealing the joints of interlocking pavers.

Manual

Manual weed control in these settings is practical only where small numbers of weeds are present.

Physical

Flaming, infrared/heat radiation, and hot water/steam treatments. Flaming of small weed seedlings is effective. Successful flaming of mature perennial weeds has also been reported; these examples have involved repeated applications over at least one growing season. This technology has been used for weed control in Europe for more than 50 years. Infrared radiation is similar to flaming and has also been successfully used in Europe for a decade or more. The proper technique is essential for success. Experimentation in refining application methods is often necessary. Field testing has shown that flaming is most effective when holding the flamer a few centimeters above the plant, rather than directly on it. The objective is to heat the sap in the plants to the point where cell walls expand and rupture, not to completely burn off the tops. Hot water and steam treatment systems have also been recently developed and operate on a similar principle. Application settings include hard-surfaced and gravelled features in urban areas.

The infrared technology was developed by the Dutch and just recently introduced to North America. While details of treatment cycles and effectiveness have not yet been determined for specific situations in North America, the technology looks promising for application to paved, gravelled and other such areas. There are currently two hot water/steam treatment systems available which are at a similar state of development to the infrared/heat treatment system.

All methods of weed removal in paved areas (i.e., concrete and asphalt pads, pathways, and streets) should be coordinated with a crack sealing program to help prevent recurrence of the weeds.

Chemical

Contact and/or systemic post-emergent herbicides may be necessary in conjunction with a crack sealing program to remove extensive developments of invasive perennial weeds, particularly resprouting woody species such as willow and cottonwood.

Weeds in Joints and Cracks of Streets, Sidewalks and Other Hard-surfaced Areas

Target/Host
Street and sidewalk cracks, especially where the gutter bar meets the street pavement.

Symptoms/Typical Damage
Weeds germinate and grow in cracks and joints.

Potential Indirect Treatment Strategies

Habitat Modification

Clean and seal cracks and joints in asphalt and concrete. Periodically reseal as needed to prevent the development of new openings where weeds can develop.

Design and Construction

New streets should include a unified curb and gutter, which eliminates the joint between the gutter bar and the curb. This is an example of an IPM design that results in fewer weed problems.

Manual

Manual weed control in these settings is practical only where small numbers of weeds are present.

Mechanical

A revolving wire brush on a hydraulically operated arm attached to a street sweeper may be used for weed control along streets where the gutter meets the street pavement. Vegetation removed by the wire brush is collected by the street sweeper.

Physical

Infrared radiation and flamers. (See prescription for Weeds in Hard-Surfaced Areas.)

All methods of weed removal along streets and sidewalks should be coordinated with a crack sealing program to prevent recurrence of weed control problems.

Chemical

Contact and/or systemic post-emergent herbicides may be necessary for initial weed removal in conjunction with a crack sealing program.

Source: IPM Access - An Integrated Pest Management Online Service

All materials copyright IPMPA unless otherwise noted. All rights reserved.

E-Mail: ipmpa@efn.org
URL: http://www.efn.org/~ipmpa
Voice: (503) 343-6969 [office] or (503) 345-2272 [message]