Gardening offers many pleasures, from the joy of getting our hands in the soil to seeing the beautiful flowers that are the culmination of our efforts, but it has its share of challenges, too. One is the inevitable appearance of unwanted bugs or diseases that afflict foliage. As a professional nurseryman, I’m finding that gardeners are turning more and more to holistic solutions for these problems. They are learning that healthy plants can more effectively ward off diseases and, in doing so, they have discovered the most important step in what has come to be called Integrated Pest Management (IPM). Every gardener has already experienced this aspect of IPM—choosing the right plant for the right spot, starting with healthy soil, and giving that plant the right amount of water and nutrition. IPM also has valuable tips for dealing with pests once they do appear, all using organic or non-toxic solutions.
Although information on IPM is out there, I have attempted here to gather its most important tenets so that you may incorporate its practices into your daily gardening and fashion what all of us want: a beautiful and environmentally friendly slice of paradise.
What is IPM?
Integrated Pest Management is a comprehensive approach to removing or controlling common destructive garden insects and frequently occurring diseases. This approach encompasses the use of beneficial insects that eat or stop unwanted insects, organic or natural insecticides rather than harmful pesticides, and helpful gardening practices that minimize the occurrence of unwanted pests. The overarching goal is to promote a healthy environment and a garden that can prosper without harmful insecticides.
What is a Pest?
“Pests are organisms that damage or interfere with desirable plants in our fields and orchards, landscapes, or wildlands, or damage homes or other structures,” according to the University of California Agriculture and Natural Resources program. Pests come in many forms—including bacteria, viruses, fungi, animals, and other plants—and can cause disease or harm ecosystems.
As gardeners, we are most concerned with harmful insects and diseases found on plants or in the soil. To understand plant pests and diseases, we must first look at soil, which supports not only plant pests but also their allies. After reviewing beneficial microbes, insects, and arachnids, we will cover some common pests as well as the gardening practices most effective at controlling them.
Healthy plants are the best defense against unwanted pests and diseases and soil health is one of the key factors in growing healthy plants. Knowing the type of soil where each plant will thrive is the first order of business. This can vary between fertile, humus-rich soil for many edibles and ornamentals to low-nutrient but highly porous, fast-draining soil for succulents and desert or dry garden plants. Soil pH may also play a role. For example, acid-loving shrubs such as rhododendrons, azaleas, hydrangeas, camellias, and fuchsias all want soil with a lower pH (more acidic). The University of Vermont Department of Plant and Soil Science explains that soil pH “influences several soil factors affecting plant growth, such as soil bacteria, nutrient leaching, nutrient availability, toxic elements and soil structure.”
Beneficial Soil Microbes
Numerous soil microorganisms help plants obtain otherwise unavailable nutrients by converting these nutrients into a plant-available form in exchange for energy from their hosts. These microorganisms also stimulate plant growth without increasing nutrient availability to plants. Certain beneficial bacteria and fungi achieve this stimulation through the production of metabolites or by their physical interactions with host plants.
Beneficial microbes also help to control plant diseases by feeding on pathogens (called antagonism), by competitive exclusion, and by competing for nutrients or space by producing metabolites that kill pathogens or inhibit their growth and movement (microbiostasis). They may also stimulate or prime the plant’s own natural defense system. Generally, disease-suppressive microorganisms work best at preventing rather than curing diseases.
Beneficial Insects and Arachnids
Using beneficial insects in your garden mimics nature’s own checks and balances, where harmful insects are kept under control by beneficial insects that eat them. Like all living creatures, beneficial insects have a basic need for water, food, and shelter. By providing these things, your garden will become an inviting home for them. A diversity of plants will attract a wide range of insects. Many beneficials appear in the garden before the pests and need alternative food sources such as pollen or nectar if they are to stick around.
Some of the best beneficials are listed below, and the first three are commonly available in nurseries. Meanwhile, keep an eye out for the appearance of other beneficials in your garden and leave them to work for you.
Ladybugs. Before they get their bright red colors, they start out life as larvae, cruising around on plants and feasting on aphids. Ladybug larvae can eat up to 40 aphids an hour!
Green Lacewings. Larvae feed on aphids, thrips, whitefly, leafhoppers, spider mites, and mealybugs. Adult green lacewings feed on pollen and nectar, but their larvae, which look like an odd mix between a slug and an alligator, prey upon soft-bodied garden pests, including caterpillars and aphids.
Praying Mantises. These fierce predators hunt many insect pests that terrorize gardens, including moths, beetles, and flies. Note, however, that praying mantises are ruthless and will turn to eating other beneficials, such as butterflies, bees, and hummingbirds.
Spiders. Spiders are often overlooked as beneficial, but they are remarkably effective pest controllers, feeding on insects or other unwanted arthropods.
Parasitic Wasps. Many species of tiny wasps lay their eggs in pests such as aphids or caterpillars. Hatching larvae consume the pest and kill it.
Ground Beetles. This group includes a large variety of predatory beetles that are beneficial as both adults and larvae. Larvae will eat a wide range of insects, including nematodes, caterpillars, thrips, weevils, slugs, and silverfish.
Hoverflies. Looking like a tiny yellowjacket without a stinger, the hoverfly in its larval stage is a voracious predator, killing aphids, caterpillars, beetles, and thrips.
Effective Gardening Practices
Growth Conditions. It cannot be overstated that the best defense against harmful insects or disease is healthy plants. You can effectively discourage pests by modifying the way you design, irrigate, fertilize, and manage your garden. Beneficial design practices include planting pest-resistant or well-adapted plant species such as native plants.
There are four main factors for growing and maintaining healthy vegetables or ornamental plants.
Soil. Providing nutritious soil is equivalent to giving humans organic food. Fertile soil promotes development of strong and healthy roots, leading not only to vigorous growth but to a plant’s ability to fight off disease. Additional organic fertilizer may help plants at a future date.
Light. Place your plant in the light conditions it most favors. Sun-loving plants located in too much shade will struggle, inviting pests and disease. Conversely, plants that need protection from midday sun will burn or dry out in too much sun. Most gardens have a surprising variety of microclimates, allowing gardeners to give each plant the environment that promotes its prosperity.
Water. Providing the proper amount of water usually includes making sure that the soil allows for good drainage and proper soil aeration. Waterlogged plants will struggle and likely die, but if the soil can’t hold onto some moisture, the roots will be unable to provide the leaves and flowers the moisture they need.
Circulation. Plants that can get bushy—such as shrubs and dense perennials—will need occasional pruning to open space within the plant for proper air circulation. If plants are too dense with leaves, they can be prone to fungal diseases, and any unwanted insects on the plant may be hard to spot.
Pest Control. One of the prime tenets of IPM is to avoid using harmful pesticides that weaken plants or kill off beneficial microbes in the soil. Use pesticides only if other controls are ineffective and pests are reaching intolerable levels, which is rarely the case when practicing integrated pest management principles. Fortunately, there are a wealth of organic or nontoxic treatments on the market. These include insecticidal soaps and oils, as well as microbials such as Bacillus thuringiensis and spinosads.
The first step when one has an insect problem is to squash, trap, or wash off these pests. This is relatively easy for common insects like aphids and mealybugs, but one can also strip off scale from the trunks or branches where they appear using a thin glove or rag. One valuable tool for ridding plants of soft-bodied insects is the Bug Blaster. This nozzle simply screws onto the head of a watering wand and, as its name suggests, blasts bugs off plants using a fine but concentrated spray of water. It’s especially useful for getting rid of problematic whiteflies.
95% of all common garden disease or insect problems fall into three categories. Each of these problems have a recommended organic or nontoxic treatment.
Soft-bodied Insects. I recommend using a solution with pyrethins, which are extracted from chrysanthemum flowers. This solution is effective for killing aphids, mealybugs, and scale. I recommend spraying it in the early evening when bees are no longer foraging for nectar. As an alternative, you can use Neem Oil or Insecticidal Soap.
Chewing Insects. This group includes thrips, leaf miners, caterpillars, and mites. Thrips and caterpillars especially can do a lot of damage in a hurry. Use a treatment with spinosad in it. Spinosad is a natural substance made by a soil bacterium that can be toxic to insects. It works by paralyzing the insect’s nervous system, causing their death, typically within one to two days. It does not harm the plant. Bt (Baccillus thuringiensis) is also an effective and organic treatment for caterpillars.
Fungal Diseases. The most common fungal diseases include powdery mildew, black spot, and rust. Powdery mildew is easily dispensed within 24 hours by using a natural copper fungicide. Black spot affects many plants, most notably roses. Though spraying with copper fungicide won’t get rid of spots on leaves, it will arrest the progress of further problems. The same is true for rust, seen most notably on plants like hollyhocks and lavateras, as well as on vining vegetables like squash.
IPM Institute of North America, What is Integrated Pest Management?
Our Water, Our World, IPM Advocates
University of California Agriculture and Natural Resources, UC IPM Statewide Integrated Pest Management Program
University of California Agriculture and Natural Resources, What Is Integrated Pest Management (IPM)?