Resist the Urge to Spray

The natural tendency of many people in the garden is to 'nuke' the garden with chemicals for anything they see attacking their plants. Incorrect diagnosis of plant problems in the garden can lead to misuse of many garden chemicals and, ultimately, account for ineffective treatment. Often the incorrect use of chemicals aggravates the original problem. For example, problems with spider mites increase with the application of insecticides that kill their natural enemies. Many people incorrectly associate damage symptoms with an insect that happens to be on the plant at the time, when in fact that insect has not caused the damage and may even be beneficial by feeding on the insect pest. Many plant problems are not caused by insects or disease but are related to temperature extremes, over-watering, drought, damage caused by lawn mowers, or overuse of chemicals. Most typical garden problems can be reduced or even eliminated by using good gardening practices and preventing problems before they have a chance to start. Many plants become more susceptible to pest attack if they are stressed. Pest prevention is often simpler and cheaper than pest removal.

The first step in plant damage diagnosis is to determine if a problem really exists. Since all the organisms in a garden will influence the overall working and functioning of the plants and the garden as a whole, any action taken by the gardener may have an effect on plants or animals other than those being treated. When considering pest or disease control it is critical to be aware of such effects. Few yard and garden problems are simple enough to be solved simply by spraying pesticides. Whenever possible, take action to prevent problems before they occur by choosing pest resistant varieties and providing optimum conditions for growth. Using plants that are well-adapted for Missouri soils and summer heat will ensure optimum health of a plant, thus the plant will be better able to tolerate pest injury. Most insect infestations or disease infections do not require chemical control. Grasshoppers defoliating an apple tree in September does not merit control since the leaves will die back shortly anyway. Additionally, if you are harvesting the fruit, you can tolerate insect damage to the leaves. One or two caterpillars on a tomato plant can be easily picked off versus treating with a chemical. Aphids or spider mites attacking roses, peppers or tomatoes are very easily removed from the plant using a strong water spray. Good garden hygiene such as pruning out infested plant material and planting resistant plant cultivars is crucial to reducing pest problems. And added benefit of the above control methods is the preservation of beneficial insects. Be sure to ask yourself, for the sake of the environment, if you can tolerate a few more weeds and insects in your yard.

Proper pest identification is essential for choosing correct control actions. Closely related insect species may require different management strategies and most insect species require no action at all. Many insects can be controlled using mechanical methods which are nonchemical materials that reduce pest abundance directly. Examples of mechanical control are; controlling weeds with mulch, mowing, weed eaters, flaming, or hand pulling; destroying or removing disease or insect infested foliage by hand-picking, pruning, or high-pressure water sprays; and preventing insects from feeding on plants by using floating row covers, sticky material around tree trunks, and barriers or collars around the base of plants. Using natural enemies (predators and parasitoids) such as ladybird beetles to control insect pests is another method of control. Predators and parasitoids are constantly at work in gardens and occur naturally in most any location. Many natural enemies are killed by broad spectrum insecticides so the avoidance of these chemicals whenever possible will aid in the occurrence of natural enemies in the garden.

When it becomes necessary to use chemical control it is best to obtain environmentally friendly chemicals such as insecticidal soaps, horticultural oils, and natural plant products such as pyrethrins, rotenone, and sabadilla. There are many types of control methods that can be used effectively to manage insect pests. Proper insect diagnosis is critical when choosing a control method as insects respond differently to different control approaches. Mouthparts also play a role in how an insect reacts to a particular chemical control. Insects have two types of mouthparts; piercingsucking or chewing. Insects with chewing mouthparts such as grasshoppers, beetles, caterpillars, bees and wasps have a hardened pair of mandibles (jaws) that work sideways for grinding and cutting. Damage caused by insects that chew leaves is often more unsightly than harmful to the plant. Insects with sucking mouthparts include aphids, scales, mealy bugs, leafhoppers, true bugs, moths and thrips. With these insects, the mouthparts are elongated to form a tube that punctures the plant tissue and allows the insect to remove fluids from the plant. Many insects with sucking mouthparts can transmit disease to plants or inject toxic substances into the plant during feeding. Choosing the best chemical for insect control depends upon which type of mouthparts you are dealing with. Always consult the product label to determine whether or not the chemical is effective against the pest you are dealing with and if the product is safe for the plant that is being damaged and be sure to follow the application procedures carefully.

Learn when and where pesticides may be needed to control problems. Pest identification is extremely important to determine if you need to consider treatment and, if so, what type of treatment. For positive identification of garden pests, you can contact your local University of Missouri Extension County Office. Listed below are resources that I used writing this article and are very useful for insect and disease identification. The University of Missouri Extension also has guide sheets available online. These guide sheets help identify common garden pests and treatment options available for those pests. That site is located at http://muextension.missouri.edu/explore.

Useful Garden References
Greenwood, P., A. Halstead, A. R. Chase, and D. Gilrein. 2000. American Horticultural Society Pests and Diseases: The Complete Guide to Preventing, Identifying, and Treating Plant Problems. Dorling Kindersley Publishing, Inc.

Cranshaw, Whitney. 1998. Pests of the West. Fulcrum Publishing.

Gilkeson, Linda, Pam Pierce, and Miranda Smith. 1996. Rodale's Pest and Disease Problem Solver. Rodale Press.

Barrett, Bruce. Managing Insect Pests in the Home Vegetable Garden. University of Missouri Extension, Publication M163.

Mary Kroening,
State Master Gardener Coordinator, University of Missouri,
573-882-9633