Lawn and Garden

Insect Pest Management in Fruit and Vegetable Gardens

By Daniel Frank, WVU Extension Service entomology specialist

Insects are the most diverse group of organisms on Earth, representing well over 50% of all described species. Although certain insects can cause problems in the garden, it is important to remember that these pests represent only a tiny fraction of the insect species around us. Many insects are directly beneficial in their role as pollinators, predators of pests, and decomposers of plant and animal material. Many other insects are important indirectly as food for other animals.

Controlling or managing the insects that do become pests is best accomplished by using a process called Integrated Pest Management, or IPM. IPM focuses on long-term prevention of pests by using a combination of cultural, mechanical, biological, and chemical tools. Preventing pest problems before they occur is a key principle of IPM. This means regularly monitoring your garden and learning to identify pest and pest problems, as well as beneficial organisms. Early detection of insect pests or their damage may also give the home gardener more options for control.

Insect Identification

The first step in IPM is identification of the pest. When an insect pest is identified, it is possible to understand its life cycle and its relationship to the plants at risk. This knowledge is important because not all control tactics are successful for all pests or life stages. Correct identification can also help prevent beneficial insects or other organisms from being mistaken as pests.

General information concerning insects, their development, and potential injury are discussed below. More information on specific insect pests and their identification can be found in a number of resources such as Cooperative Extension publications and fact sheets, the Internet, or guide books. Live or well-preserved specimens may also be taken to your local extension office for identification by county agents or specialists.

General Characteristics. Insects belong to a group of organisms called Arthropods. Major characteristics that distinguish Arthropods from other animals include jointed legs, a segmented body, and a hard skeleton located on the outside. Spiders, mites, millipedes, and lobsters are also Arthropods. Insects differ from these other Arthropods by having three pairs of legs, a segmented body divided into three regions (head, thorax, and abdomen), one pair of antennae, and usually two pairs of wings in the adult stage.

Development. grub During an insect’s life cycle, it will undergo metamorphosis, or a change in form. Most insects follow one of two patterns of metamorphosis – complete or incomplete. Insects that undergo complete metamorphosis have four distinct life stages (egg, larva, pupa, and adult). The egg hatches into a larva, or the immature stage of the insect’s life cycle. During the larval stage, the insect is actively feeding and growing. Caterpillars, grubs, and maggots are examples of different types of larvae. When it is time for the larva to become an adult, it goes into the pupa stage. The pupa is an inactive, transformation stage where the larval tissues are reformed into the adult. After pupation, adults emerge with fully formed wings and reproductive organs. Insects that go through complete metamorphosis look very different at larval and adult stages. Larvae may be so different from adults that they do not eat the same food or live in the same habitats. Bees, beetles, flies, and moths are examples of insects with complete metamorphosis.

aphids Insects that undergo incomplete metamorphosis have three distinct life stages (egg, nymph, and adult). The nymph is the immature stage, which often looks like a smaller, wingless version of the adult. As the nymph grows, it slowly matures into an adult with fully formed wings and reproductive organs. Nymphs usually eat the same food and live in the same habitat as the adults. Aphids, cicadas, grasshoppers, and stink bugs are examples of insects with incomplete metamorphosis.

Injury to Plants. catepillars-eating-leaf Insects can injure plants by chewing, sucking, or boring into leaves, fruits, stems, or roots. Some insects can also cause galls and abnormal plant growth, or transmit plant diseases. Common signs of insect damage include defoliation or distortion of leaves, chewed holes in plant tissue, and discoloration of leaves, blossoms, or twigs.

Insect feeding damage can be classified as direct or indirect. Direct damage occurs when insects feed on the harvested portion of the plant. There is generally little tolerance for these insect pests in the garden. Indirect damage occurs when insects feed on roots, stems, or leaves. Most gardeners can tolerate some level of indirect damage; however, large populations of indirect feeders may cause significant decline in the quantity or quality of the harvestable portion of the plant.

Controlling Insect Pests

In IPM, prevention is the first line of defense against a pest population. Pest problems can often be prevented by choosing pest-tolerant plants that are well-suited to the soil and climate in which they are grown. Removing small infestations before they become a problem is also helpful. If control of a pest is necessary, it is often best achieved by using a combination of cultural, mechanical, biological, and chemical control strategies. Specific techniques that can be used for control often depend on the insect pest identified.

Cultural Control. Cultural control is the practice of modifying the growing environment to reduce the occurrence of unwanted pests. Examples of cultural control include sanitation, weeding, planting or harvest timing, and crop rotation.

Sanitation. Destroying or removing infested plant and trash materials from the garden can be an effective way to reduce insect pests or their spread. Destruction or removal can be achieved by tilling, burning, or pruning.

Weeding. Some weedy plant species can serve as hosts for insect pests that move into the garden later in the season. Keeping garden borders mowed and trimmed is one way to help control these insect pests.

Planting and harvest timing. For many fruit and vegetable crops, planting and harvest time can vary within certain limits. Since many pest species are less numerous early in the season, an early planting of vegetables may escape with little or no damage. Similarly, harvesting crops earlier in the season may also minimize insect feeding injury.

Crop rotation. When a certain crop is grown in the same location year after year, certain insect pests can become established in the soil, resulting in a more rapid infestation each year. Planting a crop in an area of the garden where it or a related crop has not been previously grown may help prevent or delay pest damage.

Mechanical Control. Mechanical control involves the use of hands-on techniques as well as simple equipment and/or devices to reduce the occurrence of unwanted pests. Examples of mechanical control include handpicking, barriers, and traps.

Handpicking. When pest numbers are low, hand removal of insects is one of the simplest ways to prevent the buildup of pest populations and resulting damage. Removed insects can be destroyed by crushing or drowning in soapy water.

Barriers. Physical barriers can be an efficient way of excluding insect pests from your plants. For example, collars made of toilet paper rolls or tin cans can be placed around the base of individual plants to protect the upper plant parts from crawling insects that live in the soil or to protect the stem base from egg-laying. Row covers, which are light- and water-permeable, are another type of barrier that can be used to protect a crop from migrating insects.

Traps. Although traps are generally used to monitor certain insect species, they can also be used for removing pests. Some traps attract insects by color. Two examples are colored cards covered with a sticky substance and bowls filled with soapy water. Other traps use a chemical scent (pheromone) produced by a particular insect species to attract other members of the same species to the trap.

Biological Control. Biological control relies on naturally occurring organisms to reduce the occurrence of unwanted pests. In some instances, this can be another insect that attacks the pest. It can also involve the action of other organisms, such as microbes, spiders, birds, or toads. Designing and managing gardens to attract and preserve these beneficial organisms should be a top priority. Growing flowers or herbs among your crops or along borders is a good way to attract beneficial insects. Using chemical controls only when necessary and using those that are considered less harmful on beneficials can also help preserve existing populations.

Chemical Control. If pest populations reach damaging levels despite preventative measures and other types of control, chemical insecticides can help you avoid losing your crop. Consider first those insecticides that are considered “low impact” or that cause the least possible harm to beneficials and the environment. Although insecticides are specifically designed to kill insects and many other arthropods, they can also be harmful to people and pets. Chemical insecticides can generally be divided into two broad categories – organic and synthetic. These insecticides can also be grouped into different classes according to their mode of action or method of killing the insect.

Organic insecticides. Organic insecticides are chemicals that are derived from natural sources and are not synthetically manufactured. Many organic insecticides include products that contain botanical poisons such as pyrethrum or neem extracts, inorganic minerals such as sulfur or kaolin clay, or products derived from microbes such as spinosad. Insecticidal soaps and horticultural oils are also considered organic options. The term “organic” does not automatically mean these products are safer than synthetic insecticides. Many organic insecticides can be harmful to beneficial insects and, in some cases, to people and pets.

Synthetic insecticides. There are many types of synthetic insecticides. Common synthetic insecticide classes include organophosphates, carbamates, pyrethroids, neonicotinoids, and insect growth regulators. Some of these compounds (pyrethroids and neonicotinoids) are synthetic equivalents of botanical insecticides. Others such as insect growth regulators mimic certain insect hormones.

Application of insecticides. When using any type of insecticide (organic or synthetic), follow the directions on the label carefully. The label attached to the insecticide container provides specific information on its proper use, safety precautions, and disposal. Although insecticides can be effective, they are not a foolproof way of controlling insect pests.

Insecticides may not be as effective during certain stages of the insect life cycle, or the insect can develop resistance to certain insecticide ingredients. In these cases, the use of an insecticide might do more harm than good. If multiple insecticide applications are required, and unless otherwise directed on the insecticide label, it is highly recommended that you rotate insecticide use with products that have different modes of action to delay the development of resistance to any one product.