Steps to Controlling Insect Pests in the Garden

From a horticultural perspective, gardeners encounter three types of pests: weeds, diseases, and insects. This article offers a strategy for managing and controlling insect pests frequently found in home gardens.

Each garden "type" may, or may not, have insect pests specific to the precise garden. For instance, a squash vine borer will likely be found only in vegetable gardens containing members of the cucurbit family, while Japanese Beetles may be found on roses in ornamental gardens as well as on beans in vegetable gardens or raspberries in a small fruit or berry garden.

The good news for home gardeners is that control and management practices can be optimized to meet an acceptable level of insect damage for each individual gardener. Integrated Pest Management ("IPM") is one strategy for managing insect pest damage in home gardens and landscapes.

• IPM is a decision-making process that seeks the least toxic method for controlling pests.
• IPM does not mean the total eradication or extermination of a pest.
• Past experience has shown that regular applications of pesticides will result in populations of insects that are pesticide-resistant.
• Gardeners can best manage pest populations by using a variety of control methods.

The IPM Triangle

Control methods range from the least toxic option (triangle base) to the most toxic option at the apex. There are different versions of the IPM Triangle, but regardless of the model used, the basic premise is the same: begin pest management controls at the base and gradually move up the triangle, progressing through different control/management layers. This model may be used in different types of gardens; however, the examples included in this article are primarily for edibles.

In this IPM Triangle, the base segment consists of cultural methods of control and includes activities such as proper plant selection, keeping the garden clear of diseased plants, using crop rotation, and planting a cover crop.

The next segment is referred to as the mechanical/physical control layer. In this layer, gardeners may use row covers to create a barrier, thereby protecting the growing plants from insects. Also included in this layer is weeding/mulching/cultivating the plants and removing diseased plant parts or the entire plant, as the case may be.

At the top of the triangle sit the most toxic options, and this segment is often referred to as the chemical layer and generally includes application of synthetic pesticides.

One note regarding the IPM Triangle, in some models, the top segment will also include the use of biological controls such as predatory wasps and the release of beneficial insects (i.e., ladybugs and lacewings). Some gardeners prefer to use biological controls in the base layer as a means of cultural control. The overarching concept of IPM is to present gardeners with several options for the control and management of all pests: insects, weeds, and diseases.

Having a systematic approach to pest control is helpful. When considering types of control/management for insect pests, you may want to try this sample approach:

1.  Make a list of plants in your garden(s)
2.  Identify insect pests common to each plant on the list
3.  Sketch the lifecycle of each pest and identify the type of mouthpart at each stage of development
4.  List IPM methods for each insect according to the stage of its life lifecycle

At first glance, this may seem rather labor-intensive.  If viewed as a winter task, it may seem less daunting.

Example

The crux of this exercise is to know what pests you are likely to find in your gardens based on what plants you've selected. Using the common bean, Phaseolus vulgaris, as an example, the list may include:

Plant Name:  Common bean, Phaseolus vulgaris

Common insect pest(s):  Japanese Beetle (using one pest for the example; there are more)

Lifecycle of the Japanese Beetle: This insect has four stages: egg, larva, pupa, and adult. When an insect passes through these four stages of development, the insect is said to undergo complete metamorphosis. Damage is caused at the larva (grub) stage and the adult stage, with grubs feeding on roots and adults chewing leaves.

Control Methods: At this stage, a gardener can devise a control and management strategy based on the IPM triangle and informed by the gardener's individual tolerance for insect damage.

Upon completing the exercise above, gardeners can apply this information during the growing season to the four basic steps of IPM:

1.  Observation
2.  Identification and Diagnosis
3.  Selection of Appropriate Control Methods
4.  Observe Results

1. Observation

Many gardeners find it helpful to take a morning and evening walk through the garden and scout for insects (and other pests). Hand-picking insect pests during the walk is an easy way to reduce the number of pests. Deposit the pests in a bottle of water and empty it when necessary. Insect types and activity level may vary by ambient light. So, when walking in bright light different insects may be more visible than when walking at dusk.

2. Identification and Diagnosis

Use the walkabout as a tool and look for damage to the plants. The type of damage to a leaf, for instance, will help to narrow the possible insect pests. For example, if there are small holes in the leaves, flea beetles may be present in the garden. If the margins of the leaves look as if they've been chewed, suspect an insect with chewing mouthparts such as a caterpillar.

A word about mouthparts. Insects are sometimes classified by differences in body parts, including mouthparts. Briefly, there are four different mouthparts in insects: chewing, piercing/sucking, sponging and siphoning. Noting the type of mouthpart on the insect inventory list will help to diagnose what insects are present in the garden.

3. Selection of Appropriate Control Methods

Gardeners can choose from an array of control methods as discussed above including those methods outlined in the IPM Triangle. A primary consideration for selection is whether or not a gardener uses organic growing techniques. If so, there are many options for insect controls. Two examples of organic pest control materials include Spinosad (specifically for insect control) and Kaolin clay, an ingredient used in insecticides and disease control materials.

When selecting control materials, always follow label directions; more is not better.

4. Observe Results

This last step is very important and can be used to make adjustments to future insect pest control methods and management techniques. Keeping a garden journal is an excellent tool for recording not only results of insect control methods but of many garden-related tasks.

Controlling and managing insect pests in a garden is an integral part of gardening. Tools for doing so abound and offer gardeners great latitude in managing a garden. The key is to find an approach that is consistent with your growing style and one that fits comfortably into not only your financial budget but also complements the amount of time you are able to allocate to maintaining a garden.

References

Ask a Biologist: True Bugs. Arizona State University

The Types and Stages of Insect Metamorphosis, Thought Co.

Japanese Beetle (Penn State Extension)