A healthy approach to garden pest management

For as long as human beings have been cultivating crops and growing ornamental plants, pest control has been an important to-do. Anyone who grows plants for food or pleasure must also be concerned with the organisms that might harm those plants.

The word “pest” in garden lingo is fairly all encompassing. It can refer to animal species that consume and damage plants or spread plant diseases—gophers, rats, and other mammals; insects such as aphids, caterpillars, mealybugs, and mites; or other critters such as snails, slugs, and nematodes. It can refer to weeds or parasitic plants—bindweed, dandelions, mistletoe, spurge, and more. Or, it can refer to fungi, bacteria, and viruses—living organisms that are neither plant nor animal—some of which can harm plants.

Over the centuries, conventional wisdom about how to successfully manage plant pest problems has evolved. I recently stumbled across these two fascinating turn-of-the-century tidbits from an 1879 Illinois newspaper, advice we’re unlikely to follow today:

“For lice upon plants, syringe with a solution of soap and whale oil.”
“Very weak lime water will kill worms in flower pots.”

Successful pest control is a delicate balance. On the one hand, it’s important to manage plant pests so that they don’t do excessive harm. On the other hand, it’s critical to use the most effective and least toxic pest control approach to avoid serious environmental damage and human health concerns.

Integrated Pest Management (IPM) is the modern standard for pest control, based upon many decades of scientific research. It’s defined as “an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques such as biological control, habitat manipulation, modification of cultural practices, and use of resistant varieties.”

There are several key components to a successful IPM program:

  • Rule 1: Identify the pest. Just as you shouldn’t take a medicine without first diagnosing an illness, so you shouldn’t take any action before knowing precisely what your pest problem is. Inaccurate diagnosis can lead to an ineffective or even detrimental treatment program. If you’re uncertain of what pest you’re dealing with, use the services of our local Master Gardener hotline at (209) 953-6112 or the San Joaquin County Agricultural Commissioner at (209) 953-6000.
  • Rule 2: Choose the right control method. Very often, pest problems can be solved by using one or a combination of simple, non-toxic measures, without resorting to the use of chemicals. (More about this below.)
  • Rule 3: Evaluate the control and develop a pest management plan. This common sense and business-like approach means you should monitor all pest control methods to check their effectiveness, and then formulate an approach for the future.

Plant pest problems can often be easily prevented or minimized. Select plant species or cultivars that are disease-resistant and well adapted to the growing conditions in a particular space. Practice proper garden sanitation by cleaning tools regularly and disposing of diseased plant material properly. Water, prune, and fertilize plants in the right way at the right time to avoid stressing them and compromising their natural self-defenses.

Pest control methods can be grouped into several categories:

  • Cultural Control. This means changing plant care activities to reduce pest problems. For example, crop rotation helps minimize pest problems in edible gardens and agricultural plots. Also, landscapes with diverse plantings are less susceptible to pest problems than monocultures.
  • Mechanical Control. This simply means using some kind of physical action. Some examples: using a strong stream of water to spray off aphids or scale insects; hand-pulling weeds; using non-chemical traps; hand-picking caterpillars and snails; and using screens, barriers, netting, or mulches to exclude animals, insects, and weeds.
  • Environmental Control. Water, sun exposure, and soil conditions can affect plant health. For example, overwatering can lead to fungal infection and other plant diseases. Soil solarization can reduce weed germination and soil pathogens.
  • Biological Control. There are many species of beneficial insects (aphids, lacewings, predatory wasps, soldier beetles, and more) that work to reduce populations of harmful insects. Allow them to do their job, encourage them to stay by adding their favorite plants to your garden, and remember that pesticides often kill the “helpful bugs” along with the bad ones.
  • Chemical Control. Always use pesticides and herbicides as a last resort, and be sure to follow the application instructions to the letter, because overuse of garden chemicals has many serious, detrimental consequences. (Look up “Ten Reasons Not to Use Pesticides” by the Center for Environmental Health.) One very important thing to remember when using chemicals is that more is NOT better! Pesticide labels are legally binding documents; it’s illegal and dangerous to apply garden chemicals in a manner inconsistent with the instructions.

A screenshot from the UC IPM (Integrated Pest Management) website, showing the categories of available pest resources.
















The University of California IPM website is an excellent, detailed, and comprehensive resource for use by home gardeners, agricultural personnel, or natural resource specialists. Click on “What Is IPM?” for a reader-friendly explanation, or explore the website’s many pest-specific pages. You can also refer to the “Safe and Sustainable Pest Management” chapter of the California Master Gardener Handbook; it’s available through both the Stockton-San Joaquin County Public Library system and the Lodi Public Library.

For gardening-related questions, call the UC Master Gardener office at 209-953-6112, or visit our website.

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