Cooperative Extension
MG Manual Home

  MG Manual Reference
Ch. 3, pp. 65 - 68

[ General Control Principles: preface | cultural | mechanical | biological; predators, parasites, diseases, conclusion ]


You are in the bathroom, brushing your teeth when you glance down and see an enormous cockroach. What is your first reaction? If you are like most homeowners, it is to grab a can of some chemical and spray like crazy. But this may not always be the safest, the cheapest or even the most effective way to control insect pests.
Chemical insecticides were first developed during World War II. They worked so much better than anything that had been developed up to that point that they were quickly embraced by farmers, health control officials, and eventually homeowners. But over time it has become evident that chemicals are not always the only, or even the best alternative, particularly for the homeowner.
Why aren’t chemical pesticides always the best alternative for controlling pests?
Whenever insecticides are used heavily, the resistant insects survive and reproduce until insecticides are no longer effective. Currently over 200 different insect species have developed resistance to one or more insecticides. Some species that have demonstrated resistance include houseflies and cockroaches.
Insecticides can do more harm than good because they destroy the natural enemies and competitors of the pest. For example, fire ants actually do better where certain sprays are applied because the sprays kill all the other kinds of ants, leaving room for the fire ants to take over.
Effects on Non-Target Organisms
Insecticides are not only toxic to the intended insect pest, but also to many other organisms, including beneficial insects, fish and birds. For example, honey bees are important pollinators, and are necessary for fruit production of many crops, including citrus. An application of insecticides during flowering can be devastating to the bees and to the crop.
Synthetic pesticides are largely petroleum-based, and can be very costly to produce. Also, the cost of registering a pesticide has greatly increased and this cost is passed on to consumers.
Non-Renewable Resources
Most synthetic chemicals are petroleum-based, and could become scarce in the future if we run low of non-renewable resources.


Plants under stress suffer from pest infestations more quickly and more severely. Insects may even be attracted to stressed plants.
Do Not Over Water or Under Water
Fertilize Properly
Rotate Crops (may be difficult in a small garden)
Some plants encourage a specific pest problem. If this seems to be the case, don’t plant that crop for a year or two. This will break the pest cycle.
Work the Soil, Add Amendments
Heavy soils that do not drain properly may stress plants. Soil amendments such as peat moss, compost, or forest mulch loosen the soil, and help prevent insect problems.
Arizona soils and water tend to be alkaline (pH of 7.5 or greater), which influences the effectiveness of both synthetic and natural insecticides, as well as stressing non-native plants. Most plants prefer a pH of 6.5. The addition of gypsum or soil sulfur will help alleviate this problem.
Disking or rototilling may aid in killing many overwintering or resident soil insect pests.
Plant Resistant Varieties
Some plant varieties are resistant to particular insects, but these may be difficult to locate. For example, hairy varieties of potato are resistant to aphids.
Check seed catalogs and university publications for varieties with pest and/or disease resistance.
Experiment with Companion Planting
Other plant companions are more attractive to the pest and act as a "trap crop." The insect pest builds up on the trap crop rather than on the desirable crop, and thus damage is prevented. If needed, the trap crop may be treated or destroyed to control the pests.
Plant When Insects are not a Problem
Some insects are only pests at specific times of the year. We are fortunate here in Arizona to be able to plant crops in different seasons, and avoid pests. For example, early-maturing sweet corn planted to mature by June will avoid the corn earworm, which is active later in the summer. Whiteflies are most abundant in August and September, so gardeners may want to delay planting fall vegetables until October.
Eliminate Weeds
Weeds create many pest problems, particularly cutworms. Weeds provide an alternate source of food and overwintering sites for many pests, including whiteflies. They also provide excellent cover or hiding places for slugs.
Some scientists have investigated the use of weeds or wildflowers to serve as food or shelter for beneficial insects such as predators and parasites, but the results are not clear-cut. The weeds may cause more problems than they solve if they compete with the crop or if they harbor pest insects as well as beneficials.
Keep Things Neat
Do not leave cut tree limbs or plant debris lying around. Damaged or freshly cut plant material tends to attract unwanted insects.
Avoid providing hiding places, such as old planks, cardboard boxes and overgrown weedy areas. These places provide food and hiding places for such undesirables as slugs, earwigs, scorpions, termites and cockroaches.
Old, dead leaves and other plant parts are often overwintering sites for insects and may harbor disease. Prune out dead branches, and rake up and remove old plant debris.


"The Two-Block Method"
Pick off and destroy large slow insects, such as caterpillars. Place the pest on a hard surface such as a rock, and cover with a heavy object, such as another rock. Gloves are recommended. Also, avoid "controlling" your fingers!
Hose Plants Off
A stream of water helps to control aphids, whiteflies and spider mites. Be careful, however, because some plants may burn during the summer heat.
Avoid Outdoor Lighting
Abundant outdoor lights are popular, but are not a good idea around gardens and ornamentals because they attract many different kinds of undesirable insects. Bug killer lights also may do more harm than good because they seldom catch the insects you want to control, and are known to attract pest insects away from neighboring yards. They electrocute more beneficial insects such as lacewings, nabids, parasitic wasps, etc., than pests.
Soap and Water Sprays
A gentle washing with one teaspoon to two tablespoons of dish detergent per gallon of water may control insects such as whiteflies. Some plants are more sensitive than others, so start with the lowest amount of soap and then gradually increase if no damage is seen.
Sticky Traps
Traps with a sticky material (for example, Tanglefoot®) may be used to trap insects both indoors and out. The sticky fly strip has been upgraded for use in dairy barns. Non-toxic cockroach baits may be used to attract cockroaches into sticky traps. Even mice may be trapped in some of the "industrial strength" glues used today.
Mechanical Barriers
Physical barriers such as screens, floating row covers, or strips of aluminum foil may be used to protect individual plants or small beds. Strips of aluminum foil prevent some migrating insects, such as salt marsh caterpillars.

Next Next
Search Index Comment

This site was developed for the Arizona Cooperative Extension, College of Agriculture, The University of Arizona.
© 1998 The University of Arizona. All contents copyrighted. All rights reserved.