Gardening and IPM
Karen Delahaut, IPM Specialist, University of Wisconsin-Madison

Nationally, home gardening is on the rise and Wisconsin is part of that trend. You’ve all heard that gardening will do everything from slow global warming to provide mental health benefits to those who participate. But you also know there is a dark side to gardening — pests. Whether it be insects, weeds, plant diseases or vermin there’s always something out there that upsets our Utopian plan for a tranquil backyard garden. What can we do about pests in the garden? Well, there’s always the chemical fix but that’s often not the best option. I’d like to suggest an alternative that will prevent most pest problems from coming into the garden in the first place and will reduce the severity of those pests that escape. That alternative is Integrated Pest Management.

Most homeowners view a healthy, desirable landscape as one that is sterile and in which any deviation is undesirable when in reality, each landscape represents a unique mini-ecosystem of herbivores, carnivores, microbes and fungi as well as the desirable plants. If you take a close look at natural landscapes, you will see that they are self-sustaining and diverse. There is a delicate balance between all components of a natural ecosystem. Human-designed gardens on the other hand, are often greatly simplified in the number, arrangement, and complexity of the planting when compared with undisturbed, natural environments. As a result, these simplified systems are at a greater risk for fluctuations in pest problems.

What is IPM?

Integrated Pest Management, or IPM, has been a buzzword agricultural production since the 1970's. It has its fundamental basis in plant ecology and seeks to provide the plant with everything it needs to grow and thrive. In addition, IPM integrates multiple control tactics to provide a synergistic effect of the individual components. By definition, integrated pest management is "a decision-making tool that utilizes cultural, physical, biological, and chemical pest management strategies to prevent economically-damaging pest outbreaks while reducing the risks to human health and the environment".

Key Plants

The first step toward implementing IPM in your home garden is to identify the key plants and key pests in your landscape. Key plants are those plants that provide aesthetic or functional attributes to your landscape. For example, a hedge that screens noise from the street may be considered a group of key plants in your landscape. Perhaps a mature shade tree that provides cooling shade to your home and garden is important to you. Key plants are also those plants that commonly suffer from pest problems or are routinely under stress. An example is the paper birch (Betula papyrifera). In southern Wisconsin this plant often suffers from heat and drought stress. In addition, most birch trees are plagued with leafminers annually. In this case, paper birch should be considered a key plant in the landscape. Other key landscape plants include dogwoods, maples, euonymus, junipers, flowering crabapples, pines, flowering plums, oaks, and of course roses.

Key Pests

Ten groups of insects and plant diseases account for 83-97% of all damage to landscape plants. These pests often occur annually and comprise the key landscape pests. These pests may be categorized as either generalists, specialists, or opportunists.

Generalist pests include insects like the gypsy moth that attack a wide host range of plant species. In an IPM program, management should be targeted toward the pest, not the host since the host range is so vast.

On the other hand, specialist pests include things such as cedar-apple rust which is specific only to plants in the genera Malus and Juniperus. Control of such specialist pests is best achieved through host plant resistance or biological control. By simply planting cultivars of flowering crabapple or juniper that are resistant to the disease, you will prevent future outbreaks from occurring.

Finally, opportunistic pests are those that pose a problem only for stressed plants. Wood-boring insects such as the bronze birch borer, ash borer, and two-lined chestnut borer are three examples of opportunistic pests. Outbreaks of opportunistic pests typically result from a plant being sited in an improper location. This group of pests shouldn’t be a problem in the landscape because they are avoidable given a little planning.

Monitoring

The second step toward implementing an IPM program in your landscape is to incorporate monitoring.  To effectively include monitoring into your gardening practices, you must first know what the plant is supposed to look like. Don’t confuse "golden" cultivars of a plant for chlorosis related to nutrient deficiency. Also, some contorted plants are normal while others may be giving you signs that something is wrong. You must also know your enemy. Familiarize yourself with the key pests of the plants you grow. Know when they are likely to be a problem and watch for them at that time of year. Early detection is your best defense in pest management.

Included in monitoring is the designation of threshold levels. Just how much pest damage can you stand? Often the plant can withstand more pest damage than the gardener. Because most of the plants grown in the landscape are grown for aesthetic reasons, thresholds are subjective and individual to the gardener. There’s no right or wrong here, it’s simply what you can tolerate.

Management Strategies

Prevention

So, now that you’ve identified the key plants and key pests in your landscape and have determined the threshold levels for each, just what can you do when these threshold levels are exceeded? The first thing you can do is take an offensive approach and prevent pest problems before they occur. Each planting site in your landscape has its own set of environmental conditions that will aide you in deciding which plants will best survive on that site. When selecting a site for a new planting, choose a site that offers adequate area for root expansion, sufficient space for canopy growth, adequate moisture and drainage, and the proper light conditions. Landscape designs should blend a diverse range of plant species. This diversification will reproduce the diversity found in natural landscapes and with encourage natural pest control. Landscape plants that are massed in beds are afforded more protection from environmental stresses than specimen plantings. Protective mulches placed around planting beds not only discourage weeds but also modify the temperature and moisture levels in the root zone.

Cultural practices such as sanitation will remove the source of pest problems. Raking up and disposing of infected leaves will reduce or delay pest problems in future years. Foliar plant diseases such as apple scab or powdery mildew are two diseases that can have their severity reduced in future years with a little fall cleanup. Similarly, removing dead plant material in the fall will reduce overwintering sites of some insects.

Control

Despite the fact that you’ve tried everything you could to prevent pest outbreaks, sometimes outbreaks are inevitable. In these cases, a treatment must be applied. As stated earlier, most landscape plants can withstand substantial insect or disease activity before plant health is compromised. A vigorous plant will tolerate a much higher pest population than a plant under stress. By providing water and nutrients, you may increase the vigor of a plant enough that it can utilize natural defenses to fight off pests.

Biological control in another form of "treatment" for landscape pest problems. This involves the use of natural enemies such as predators, parasites, and pathogens that attack pests. If using biological controls as a component of your pest management program, keep in mind that you must be able to tolerate a low level of the pest in order for the beneficial insect to survive. Also, there is often a lag time between the outbreak of a pest population and when the natural control agents become effective. Commercial businesses sell many beneficial organisms that can be used to reduce landscape pests to levels below your pre-determined threshold. Instead of buying natural enemies, it may be more prudent for you to conserve those natural enemies already in the landscape by reducing indiscriminate pesticide use. For more information on the use of biological controls, visit the Biological Control News website.

Finally, if all else has failed, you many choose to resort to pesticides to knock pest problems below the threshold level. When using any pesticide, it’s important to properly time the pesticide application to the most susceptible life stage of the pest. Scales for example, are most susceptible as imatures before they cover themselves with the protective covering. In this vulnerable state, less toxic pesticides such as insecticidal soap are very effective. However, if you wait too long and try to treat adult scales, even the most toxic pesticide may not provide adequate control. It’s easy to determine when to apply pesticides through the use of phenology.  Also, when using chemical pesticides, make sure you select the most appropriate material for your situation and read the entire label before buying, using and storing the product. Outdoor pesticides cannot be used indoors and pesticides that control insects on trees and flowers may not be suitable for use on food crops.

Gardening will continue to grow in popularity and with a little knowledge and planning, you can implement an integrated approach toward pest management in your landscape. If you have concerns about pest identification or management, contact your county Extension office.