Insects can offer pest control without chemicals

At the Urban Garden Center in Pearl City, University of Hawaii master gardeners offer a help-line service where home gardeners can call, email or visit with their gardening questions and samples of ailing plants.

Often, we get a picture or a sample of a plant with the question, “What is eating my plant and what can I spray?”

First, we identify the problem, which might be due to the growing conditions or microbial pathogens. If the problem is due to an insect or mite pest, we outline an integrated pest management approach, which includes growing plants that are adapted to our local conditions, maintaining a healthy and fertile soil, monitoring your garden, good cultural practices to reduce the conditions that can harbor pests and diseases, and nonchemical control practices such as growing your veggies under a protective insect screen.

As a last resort, we recommend lower-risk pesticides such as insecticidal soap or horticultural oils, which can be safer to use and sometimes more effective than pesticides that rely on chemical modes of action.

Pesticides can provide a quick fix but are rarely a long-term solution. To maintain a healthy garden, we encourage people to garden with beneficial insects instead. For example, many people know the adults and larvae of ladybugs are voracious eaters of pests such as aphids, scales and mealybugs. Other lesser-known predators include hoverflies, lacewings, pirate bugs and assassin bugs.

Even cooler are the great variety of parasitoid wasps that lay their eggs in the bodies of aphids, caterpillars and other pests. The eggs hatch and use the pest as both food and shelter until they pupate into adults.

We often get calls asking where home gardeners can buy these beneficial insects. However, to prevent unwanted introductions of pests and diseases to our unique environment, we are not allowed to import ladybugs and other beneficial insects. In addition, when you release a bunch of ladybugs into your garden, they just fly away without doing much to control your aphids.

The best approach is to attract these good insects to your garden and keep them happy by providing them with food and habitat. Though the good insects eat other bugs, they also need the nectar and pollen from flowers for energy and protein. Planting a diversity of flowers in your garden will ensure an abundance of beneficial insects. Try to provide a variety of flower shapes and sizes, and pay attention to what the bees and other insects like to visit.

Some great flowers include umbels such as dill, fennel and cilantro, and herbs in bloom such as basil and oregano. Let some of your veggies bolt, such as your kai choy and lettuce, and you’ll be pleasantly surprised at what comes to visit. At certain times of the year, fruit trees will be a good source of pollen and nectar.

Keep some flowers year-round with perennials such as our native ilima. You can also plant bunches of cover crops such as buckwheat or sunn hemp, which produce abundant flowers for weeks at a time.

To learn more about beneficial insects and pollinators in Hawaii, visit the Urban Garden Center on Saturday from 8:30 a.m. to 11:30 a.m. for our free, family-friendly Pollinators! event. You’ll find information and hands-on demonstrations about honeybees, native Hawaiian bees, Kamehameha butterflies and more.

Keiki activities include a monarch butterfly tent, build-your-own bee house, and butterfly crafts. You’ll also have a chance to buy beautiful plants for your beneficial insects, including veggies, herbs, ornamental plants, fruit trees and native plants such as ilima and mamaki (host plant of the Kamehameha butterfly). Come talk to master gardeners from UH, and learn more about how to make your garden a friendly place for bene­ficial insects and native insects.

For more information about the event, visit the Urban Garden Center website. To learn more about beneficial insects, gardening, or to contact your local Master Gardeners, click here.

Kalani Matsumura is a junior extension agent with the University of Hawaii’s College of Tropical Agriculture and Human Resources and coordinates the UH Master Gardener Program on Oahu.