Forget your idea of what a serious aphid problem looks like. Imagine one female aphid - just one - that produces as many offspring as she can, all of which survive to reproduce all they can, all of which survive, etc., etc.
In 12 generations, you will have tons of aphids.
"Gardeners aren't drowning in aphids or other pests because of parasites, predators, and pathogens (disease-causing organisms) - the three Ps of natural controls," said Howard Russell, Michigan State University entomologist. "Combined with other factors such as unfavorable weather and food shortages, these natural controls prevent pests from reaching their maximum reproductive potential."
Sometimes gardeners themselves tip the scales in favor of pests by applying pesticides that kill off the pests' natural enemies. This is a good reason for practicing an integrated pest management approach in the garden and landscape, Russell suggested.
IPM advocates the use of the least disruptive pesticide when an application is warranted, Russell noted. Dormant oils and products such as Bacillus thuringienses can be very effective in controlling certain pests with minimum impact on natural enemies and the environment. And they are safe for the gardener to use, he added.
The types of controls used in IPM include mechanical and cultural, as well as the three Ps, Russell added.
Examples of mechanical controls include hand picking tomato hornworms or potato beetle adults, larvae and eggs from plants and putting cardboard cutworm collars around pepper plants at transplanting.
Cultural controls are such tactics as rotating crops so those susceptible to the same pests and diseases don't follow one another in the garden, and cleaning up fallen fruits and leaves in orchards and rose planting to reduce the carryover of disease and insect problems from year to year. In the landscape, selecting hardy trees and shrubs that are well adapted to the conditions in the planting site will go a long way to keep plants growing vigorously and help them resist attack by pests.
Preserving natural enemies by using selective insecticides, or better yet, by not using insecticides unless they're absolutely needed is the best way to practice biological control in yards and gardens, Russell suggested. This is usually more effective than importing predators and parasites. Ladybird beetles (ladybugs) brought in to rid your garden of aphids might indeed stay there and zero in on the aphids in your roses and cabbage plants - or they might simply fly away.
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