Landscape Integrated Pest Management

Key Plants

Several studies have shown that relatively few tree and shrub species harbor most of the pest problems encountered in landscapes (3, 6, 10). These taxa can be considered as key plants for the purposes of IPM. However, other apparent plants or groupings (i.e., specimen plants and foundation plantings in conspicuous areas) that contribute significantly to the value of the landscape may also be considered as key plants for monitoring (5). Experienced arborists know which kinds of plants require intervention tactics (pest control or cultural practices) on a regular basis. This knowledge is useful in determining which plants must be inspected most closely and regularly to ensure that pests do not cause damage before remedial action is taken. Although the list of key plants will vary geographically, in most areas a small number of plants will be listed as both apparent in the landscape and susceptible to infection or infestation on a regular basis. This knowledge is comforting to arborists who may otherwise be overwhelmed by the idea of needing to spend a lot of time inspecting every plant on the property during each monitoring. In fact, although many landscape plants are susceptible to some pest species, most trees and shrubs serve as hosts for only a few key pests capable of causing severe aesthetic or physiological damage in a short time.

Key Pests

Key pests can be defined as common, ubiquitous organisms that threaten the vitality or aesthetic value of key plants. These pests range from secondary-action organisms like shoestring root rot fungi and two-lined chestnut borer that exploit weakened trees, to apparently aggressive species like vascular wilts, armored scales, and clearwing moth borers. Although there are many arthropods on nearly all plants during the growing season, few of them are capable of causing enough injury to threaten the utility and beauty of vital plants. Healthy deciduous trees and shrubs can withstand the feeding activities of hundreds or even thousands of individual sucking insects and mites and occasional defoliation by leaf-invading organisms and arthropods that cause premature defoliation. Many times, aphids and soft scales cause more problems through excretion of honeydew than from their impact on the physiological processes of the host. Landscape managers must determine which key pests in their geographical area justify significant management inputs, including cultural and other, more direct intervention activities (2). Usually, this list of key pests will be short enough to allow practitioners to become thoroughly familiar with each pest, including its host range, damage potential, biology and seasonal life history, vulnerability to management tactics, and ways to monitor its presence and abundance efficiently.

Any list of key pests for an IPM program is not complete without consideration of cultural problems associated with plants growing off-site or in confined areas where they cannot be expected to survive or thrive without additional inputs in the form of cultural manipulation. For example, junipers growing in shade will never be most productive; pin oaks growing in high pH soils will always be subject to chlorosis through limited availability of iron; dogwoods in full-sun will be predisposed to colonization by dogwood borer; taxus plants will never thrive in poorly drained soils.

Management Unit

All woody plants on small properties with limited plant diversity will usually be included in the management unit for landscape IPM programs. Even on these properties, most monitoring will be focused on key plants. As property size and plant diversity increase, it may be prudent to define the management unit as that portion of the property scheduled for intensive monitoring to maintain apparent plants in a vital condition. Other key plants may be included, depending upon consumer expectations and demands. However, woodlots on larger estates, golf courses, and institutional properties will be managed differently than trees and shrubs in the defined management unit.

Inventory/Survey

After determining which plants and pest/problems are most important in the geographical area, the IPM practitioner must become familiar with plant and pest/problem identification. A plant inventory/pest survey is then conducted on each managed property. The inventory should include plant species, a numerical assessment of each key plant’s vitality, its age or size, and its location on the property. The best approach is to chart the location of all key plants in the landscape on a map to facilitate monitoring and other aspects of IPM, including information retrieval and scheduling. Presence of all pests and their density, cultural problems, and other factors that influence inpiementation of IPM should be recorded.

Sampling Systems

Each problem included in the list of key “pests” represents a challenge in terms of efficient sampling to determine pest presence and severity. Soil should be sampled and processed to measure porosity, organic matter content, pH, and mineral element status. These tests should become routine and be implemented following guidelines provided by a local analytical laboratory. Local labs are familiar with local soil conditions, and process samples accordingly. Personnel in departments of agronomy indicate that distant labs may be competent, but their results can be erroneous, based on lack of familiarity with local site conditions and associated requirements for accurate analyses.

Key plant diseases like apple scab and fire blight may need to be managed using preventive application of fungicides in areas generally infected with these organisms. Conventional sampling may be inappropriate in these cases, because by waiting until infection occurs, it is too late to implement a control tactic that will provide an acceptable level of plant quality. However, even with these kinds of pests, plant materials need to be identified accurately so that only susceptible species and cultivars are treated. This, too, is a form of sampling: inspecting trees and shrubs to determine their identity to avoid using intervention tactics unnecessarily.

Aphid, spider mite, and lacebug infestations can be sampled efficiently by inspecting the underside of a given number of leaves in various parts of the plant canopy. With pests like honeylocust plant bug and spruce spider mite it is more efficient to hold a piece of white paper or cloth beneath branches which are then struck sharply with a gloved hand or rubber-covered stick, followed by counting the number of individuals that land on the white surface. Cloth beating trays are better than paper under most conditions, since even a slight breeze can blow specimens from a paper surface before they can be identified and counted.

Sampling for defoliators like gypsy moth and elm leaf beetle can be accomplished in a number of ways. The most efficient method is to be watchful for incipient defoliation. If properties are monitored biweekly, beginning in late April or early May, the progression of foliage loss can be tracked, and appropriate control efforts can be implemented when the action threshold is reached and before noticeable defoliation reduces the plant’s aesthetic quality.

Clearwing moth borer species’ presence and seasonal abundance can be determined by deploying “pheromone” traps that capture male moths. This is, by far, the most efficient sampling tactic available for landscape managers who wish to assess presence and vulnerability of these key pests to direct control procedures.

Knowing where to expect problem arthropods, in terms of plant material and location on the plant, and the ability to make field identification of key pests, is essential for reducing the amount of time required for sampling. Accurate records of all sampling activities, including the time required to implement individual sampling procedures, must be kept in a readily retrievable form. This information, combined with an evaluation of plant vitality, can be used to fine-tune action thresholds.

Action Thresholds

The IPM approach implies a willingness to accept some level of pest presence (7). Instead of trying to maintain a pest-free landscape, plants are managed to reduce their susceptibility to colonization and vulnerability to damage. Pest species and cultural problems are monitored routinely to ensure that they do not reach damaging levels on key and apparent plants before corrective measures are instituted.

Woody plants can support low-level infestation by many kinds of pests without incurring significant injury or having their aesthetic value reduced. The action threshold (AT) can be defined as the level of pest density at which some form of intervention is implemented to prevent unacceptable aesthetic or physiological impact on the plant. Of course, the AT for a given pest or problem will be dynamic and influenced by plant vitality, time of the year, local weather conditions, historical information about pest/problem impact in the area, and expectations of end-users. When the AT has been reached, either cultural practices are used to enhance plant vitality or to reduce the quality of the environment for the pest, or direct pest control tactics are used to reduce pest abundance.

Although the AT’s for most landscape pests have not been determined through experimentation and validation, this should not discourage use of the concept in IPM. In fact, many practitioners and homeowners use this approach without giving it much thought, whenever they detect pest presence but decide the infestation or problem is not severe enough to warrant intervention measures. Recognizing that intervention tactics should be used only when they can be justified on the basis of threat to plant quality, serious consideration must be given to establishing base-line AT’s when designing IPM programs. This is the only way the concept will ever be incorporated in the decision-making process. Prescription landscape pest control has already been implemented in Canada and will probably be mandated in the U.S. in the near future.

Realistically, the only way to get started using this concept is to initially make arbitrary decisions about AT’s for each pest/problem. Then, careful records must be kept while monitoring, including the number of pests per unit area of plant (e.g., aphids/leaf; scales/meter of branch, etc.). At the same time, there must be an estimate of plant vitality. In time, it will be possible to correlate plant vitality and pest numbers, permitting fine-tuning of AT’s. Record-keeping and experience will be required to develop meaningful thresholds for each pest on different plants at specific times of the year. In many cases, aesthetic damage occurs before pests cause measurable plant injury. Consequently, aesthetics play an important role when establishing AT’s in landscape IPM.

Monitoring

Monitoring is the most expensive part of any IPM program, so its efficiency needs to be maximized. The best way to begin developing an efficient monitoring program is to focus planning activities on key plants and key pests/ problems. Then, biological information about these plants and pests is analyzed to determine the time of year when sampling is most efficient. For example, some lepidopterous defoliators and all scale insects that overwinter on deciduous hardwoods can be assessed most easily during the dormant season. All IPM programs should include one monitoring call during the winter.

Soil sampling can be accomplished during late summer or early fall when other IPM activities have diminished. Determining the need for cultural practices at this time will permit timely implementation of tactics like fertilization and aerification to have the greatest impact on plant vitality.

Some practitioners beginning IPM programs believe they need to inspect each plant on the property during each monitoring visit. However, groupings of even high-value plants may be considered as individual plants, in terms of scouting effort, if they are comprised of one species and their branches are interdigitating. The most efficient way to handle such groupings is to monitor different plants within the grouping during different inspection periods.

All monitoring visits should include the following kinds of information: the individual plant or plant grouping (If you are mapping plants and have assigned them numbers, the best way to identify them is by referring to the appropriate number); numerical vitality rating; pest or cultural problems and their intensity or severity; damage symptoms; stage of pest or disease development; presence and abundance of pests’ natural enemies, including ladybird beetles, lacewing and hover fly larvae, and preying mantids, etc.; assessment of results of previous intervention tactics or cultural practices; general comments. This information, recorded systematically over a period of several years, will enable critical program evaluation and improvement. A simple form, specifying categories for this information, along with a place for the date of the monitoring and the location and identification of the property and its owner/manager, is an important tool in this process.

Pest/Problem-Specific Management Plans

This IPM component requires the program manager to determine how each problem encountered will be addressed, before the problem is identified during an inspection. Once a short list of key pests is developed, all available management options can be explored, and decisions made about how to deal with the pest under various circumstances that may be encountered. For example, foliage and bark sprays may be used to control bronze birch borer on susceptible landscape trees. However, if borer control is indicated for birches growing near ponds or other waterways, microinjection should be used to prevent contamination of sensitive non-target areas. Then, cultural practices should be implemented to reduce susceptibility of trees to recolonization by the borer.

Knowledge that soil compaction or high pH are serious impediments to plant health in the area, provides time to learn about tactics that can be used to solve or minimize these problems before an IPM program is implemented. If apple scab is annually a problem on susceptible cultivars of flowering fruit trees, then a phytopathologist can be consulted to determine the most efficient way to use preventive treatment to minimize scab damage. Whereas orchardists must use numerous sprays to manage scab infection of leaves and fruit, landscape managers can provide adequate foliage protection using only two well-timed applications of an effective fungicide. If bronze birch borer is a serious pest in the area, and you know that you will occasionally be dealing with trees after they are already infested, then it will be important to either become competent in trunk injection technology or develop liaison with someone who can provide this service on a timely basis.

After management plans have been developed for all pests/problems that are expected on key plants, these plans must be integrated to minimize duplication of efforts and to maximize efficiency of the IPM program. If necessary, even turfgrass pest/problem management plans can be integrated with those for trees and shrubs to develop truly holistic landscape IPM programs. This process of integration of management plans may be the most time consuming part of the planning process. But, it is also the part of the program that brings all previous planning together in the form of usable strategies for state-of-the art landscape management.

In all cases, pesticide usage will be rational, based on acknowledged need. Conventional or so-called biorational pesticides (= environmentally conservative pest control products) will be used properly: proper timing to maximize influence on the pest population and to minimize the need for re-treatment; proper sprayer and spray technique to get the toxicant to the target, while minimizing non-target impacts. In most cases, well-timed and thoroughly applied spot treatments will provide an acceptable level of control with minimum impact on natural enemies and other nontargets, including humans. Experience has shown that when pesticide use is minimized in the landscape, natural enemies of arthropods often flourish, thereby stablizing many pest populations below the AT, reducing the need for pesticides.

The value of this IPM component is that there will be few surprises or questions about procedures; decision-making will become more objective, and intervention and cultural practices can be implemented on a timely basis to reduce costs while maintaining plant vitality. Also, biorational products will often be effective because exact timing of their use against moderate pest pressure will be effective.

Logistical Management Plan

After steps 1 through 8 have been completed, it is necessary to develop a strategy for implementing the program. Decisions need to be made about how to make the transition from current practices to IPM. In most cases, a select group of clientele will be solicited, based on their previously demonstrated interest in the landscape. Another factor that influences marketing is the size of the geographical area to be considered for the new program. Experience of others indicates that an IPM alternative should be offered to a limited number of clients in a relatively small geographical area, to minimize costs/risks associated with the new enterprise. Once the program is well established and the decision is made to expand, clients or potential clients who are seeking someone to simply perform single-tactic pest control may be directed to others.

Frequency of monitoring visits is often more of a response to client expectations than to requirements dictated by pests and cultural problems. For example, four, annual, thorough inspections of all key plants for key pests/problems are probably sufficient to implement effective pest management. However, some landscape managers have learned that they must visit properties at least eight times annually to convince clients that they are receiving full value for the cost of the program. Currently, the most common monitoring plan is biweekly from May through August.

If monitoring frequency is mandated by the market, then procedures can be adjusted to minimize the time required on each property at each inspection. On large properties or where there is a great diversity of plant materials, only a portion of the plants need to be inspected during each visit. This approach is justified, as indicated, and will not reduce effectiveness of the monitoring program, even when dealing with significant, insidious problems like spider mites.

Transportation associated with monitoring and treatment implementation is costly. After listening to practitioners discuss the options for the past eight years, it appears that the best approach is to provide monitors with canopied pickup trucks containing supplies and equipment that permit spottreatment during the regularly scheduled visit, if the pest is vulnerable at that time. Besides sampling equipment, a small pruning saw, pruning shears, shovel, backpack sprayer, water, measuring devices, small containers of the most commonly needed pesticides, and pesticide application safety equipment (rubber gloves and boots, rain suit, hardhat with face shield, and respirator) will be needed. This approach minimizes travel time required to implement IPM. Of course, larger problems like aerification, fertilization, mulching, watering, and spraying large shade trees will need to be scheduled so that all properties needing these treatments can be handled efficiently. But preparedness of monitors to handle incipient or other problems during regular visits will reduce costs associated with monitoring and implemention of intervention tactics.

Monitoring will reveal presence of key pests that have not yet reached the action threshold or are not currently in a stage vulnerable to intervention. If it is a key pest that has not reached the AT, it will be scheduled for treatment at a later date. This information must be handled carefully to ensure that the treatment window is not missed.

Some IPM practitioners have found that their clients are interested in participating in the program (1). A pamphlet should be prepared to explain how the client can become involved. Watering during periods of summer or fall drought, mulching around all specimen plants and foundation plantings, and watchfulness for undetected problems are tasks that some clients may enjoy. This level of interest and cooperation is a great help to IPM programs.

Public Education

Eighty percent of the U.S. population now resides in urban areas. Most of us would agree that landscape IPM programs will benefit our society and can be used without major disruption of businesses that are now part of the green industries. However, if this transition from reliance on pesticides to IPM is to receive widespread acceptance and use, there must be a major effort in public education. Mass media will be needed to explain the concept and its value to end-users; arborists and other landscape management personnel will require training through intensive seminars and in-house training. Computer software and well-trained managers and monitors will be required. There is tremendous opportunity for those who offer a comprehensive program of plant care to the residential landscape market (1).

Linkages can be developed with landscape architects (LA’s) to further enhance an IPM practice. Since LA’s rarely seek-out landscape managers to solicit their opinions about which plant materials are appropriate for certain sites, those who maintain landscapes can inform LA’s that they have something valuable to offer. Let them know that you would like to be involved in the plant selection process to minimize future maintenance problems and costs. Provide them with specifications for installation and postplanting maintenance, including IPM. This linkage can be an inexpensive but invaluable way to attract new clients. This is a good way to lay the groundwork for acceptance of and demand for landscape IPM.

IPM specialists located at universities and those in the public sector must work together, in terms of planning and marketing, if this concept is to be accepted by consumers (1,9,11). Furthermore, joint efforts between the public and private sectors must be organized to transfer IPM technology to those who will make it operational in the landscape.

Some specialists (10) have suggested that there “is a devastating lack of detailed information regarding the biology and ecology of the major pests of ornamental plants.” And, they believed that this lack of information inhibits our ability to provide landscape IPM programs. Surely, this is not so. Admittedly, we know little about how horticultural practices directly influence plant physiology and vitality and how this is translated into resistance or susceptibility to pests. However, we know a great deal about all of the key pests that inhabit landscapes throughout North America. The critical need is to package this information in a way that is understandable and readily usable by practitioners.

Currently, there are workshops and seminars being organized to support the IPM process. The National Arborists Association has recently funded an effort to develop cook-book IPM protocols and programs for arborists. Recent graduates from landgrant institutions with Master of Science or Doctor of Philosophy degrees are joining established arboricultural firms to help plan and to provide guidance for implementing IPM. Hopefully, this will be done in the context of Plant Health Care.