Garden Mastery: Here’s how to identify and manage insect pests in your garden

Summer is the “time of the garden,” when flowers are riotously blooming and fruit and vegetables are ripening. However, you may find you’re not the only one enjoying the fruits of your labors.

In order to support their next generation, many nonvertebrate pests, such as aphids and snails, may be eating leaves, dining on fruit, and sucking juices out of your plants.

How can you manage these pests? First, you must ask yourself: How much are you willing to share your garden with wildlife?

While there is no wrong or right answer to this question, all gardeners need to draw a line at the amount of damage they are willing to endure. A garden is an ecosystem of plants and animals, with many interdependent parts. Eliminating one or more elements can affect the entire system.

Begin by identifying what is damaging your plants. While birds and other animals may be the cause, in this article we’ll focus on insect pests. This can be a challenge, given the hundreds of insect species in San Diego. Many insects are beneficial to your garden, as they pollinate your plants, eat or parasitize harmful insects, and add to the overall enjoyment of your efforts. But other insects are destructive, such as the tomato hornworm — just one can destroy an entire tomato plant very quickly.

There are many resources to help you identify what is damaging your plant. If you can actually see the culprit on its damaged host plant, you can ask other gardeners’ advice, visit local certified nurseries (bring a sample in a closed plastic bag), or contact the San Diego Master Gardeners’ Hotline (858) 822-6910 from 9 a.m. to 3 p.m. weekdays for assistance.

You can also check the University of California Integrated Pest Management (IPM) website Pest Notes or the Plant Problem Diagnostic tool (both found at If you can see the damage but not the perpetrator, you can research via garden books, and at the University of California Integrated Pest Management (IPM) website.

The eggs on these fiber stocks are Green Lacewing eggs. The larvae stage prey upon a large number of insect pests.

Friend or foe? The eggs on the fiber stocks are Green Lacewing eggs. The larvae stage of this insect prey upon a large number of insect pests, making them beneficial in your garden.

(Regents of the University of California)

After identification, your next step is to understand the life cycle of the pest and then weigh the benefits of controlling now against the benefits at a later life stage. For example, the aforementioned and dreaded tomato hornworm metamorphizes into the large sphinx moth, a nighttime pollinator important to pitahaya and other night-blooming plants. And many caterpillars are only present for a month or so before they become beautiful butterflies, so eliminating them after you have already picked most of your crop might not be worth your time and effort.

Like its name suggests, the IPM system uses an integrated method for managing pests of all types. Once you have chosen your source for pest management, monitor the effectiveness of the methods used.

Prevention is always

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Attracting Natural Insect Predators to Control Garden Pests

In the world of animals, there are carnivores (predators) and herbivores. The carnivores are meat eating, and feed on the herbivores. The same happens in the insect world, and we can use this strategy to naturally control pests in our vegetable gardens. Insect predators eat other insects.

What are Beneficial Insect Predators?

Examples of beneficial insect predators that feed on crop pests include ladybugs, lacewing bugs, spiders, wasps, certain mites, damsel bugs and many others. There are ways of attracting these insect predators to our gardens.

One of these is to create an insectary by using a diverse range of predator attracting plants.The garden insectary is a type of “companion planting”. By planting a wide range of plants you can provide alternative food sources (such as nectar and pollen, required by many predators as part of their diet) as well as habitat and shelter. For example, you can control aphids by attracting an aphid-specific predator such as Aphidius by planting lupins or sunflowers. Your insectary only needs to be big enough to hold six to seven varieties of plants that attract insects. Once these plants have matured, your beneficial insects will efficiently take over the insect pest control in your vegetable and fruit garden for you.

Tips for Setting up Your Insectary

  1. Members of the carrot family (wild carrot, dill, coriander, fennel and angelica) are all excellent insectary plants. They all produce tiny flowers which are required by parasitoid wasps. Large nectar-filled flowers can drown these tiny parasitoid wasps.
  2. Grow plants of various heights in your insectary: lace wings lay their eggs in protected, shady areas. Ground beetles like the cover from low growing plants such as mint, thyme or rosemary
  3. Flowers such as daisies and mint-like plants such as peppermint, spearmint etc will attract robber flies, hover flies and predatory wasps.
  4. Plant insectary annuals between your vegetable beds. This will lure beneficial insects as well as adding a touch of decoration to your garden.
  5. Let some of your vegetables grow to flower (carrots, broccoli, brussel sprouts, cabbage, bok choy etc).

Other Great Insectary Plants

Good insectary plants not already mentioned include the following:

  • Alyssum
  • Amaranthus
  • Convolvulus
  • Cosmos
  • Daucus carota (Queen Anne’s Lace)
  • Digitalis
  • Limonium (Statice)
  • Lemon balm
  • Parsley
  • Peonies
  • Verbascum thaspus

A garden insectary should be a permanent component of all gardens. The longer your insectary is in place, the more effective it will be as insects get to know a place that provides food, shelter and above all, a source of nearby food. Results are cumulative. As your plantings mature and resident populations of beneficial insects are established, the need for toxic chemical pesticides will diminish. Your garden will become a more natural and balanced environment for the production of healthy vegetables and flowers.…

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