One of the side benefits of gardening is insect watching. As you get to know your plants, you will become familiar with the insects they attract. When you plant something new, you will notice new kinds of insects visiting your garden.
This assumes that you find insects worthy of attention, and not just for the purpose of wiping them out. I could never understand people who supposedly love plants and nature but shudder at the sight of aphids and mealy bugs. They should invest in a good magnifying glass. I am sure that if they saw these creatures up close, they would find them of interest and, perhaps, even learn something about them.
This is not to say certain insects should be squashed. I have personally dispatched legions of cabbage loopers and cottony cushion scales in this manner, whether with my shoe or between thumb and forefinger. Hand picking and squeezing are excellent ways to begin one’s personal acquaintance with the insect community.
Immediately, you will gain appreciation for the waxy-boney cuticle that surrounds an insect’s body. You will understand why soaps and oil make good insecticides, as they slip and slide over and through this cuticle, disrupting cell membranes and blocking air passages. Insecticidal soap will effectively combat aphids, thrips and spider miles; fine horticultural oil can be used against mealy bugs, white flies, scales and caterpillar pests. With one bottle of soap and one of oil – both available in any well-stocked garden center – you should be able to keep virtually any unwanted insect under control.
Although these products are mild on the environment, their use hardly will be necessary in a garden that is properly designed and maintained. A diversity of plants that will attract a diversity of wildlife is the best defense against insect pests. You want to attract bees and wasps and flies and beetles of every kind.
Lady bugs, which belong to the beetle family, are the all-stars of beneficial insects. Each kind of lady bug may consume a different insect pest.
Microscopic parasitic wasps also are helpful. They lay their eggs in the larvae of damaging insects; and the baby wasps hatch, they cannibalize the offending larvae. Keep in mind only a small minority of garden insects are harmful.
Three families of plants are recognized for attracting a raft of beneficial insects: daisies (gazanias, coreopsis, cosmos, dahlias, sunflowers, zinnias), umbellifers (fennel, cilantro, Queen Anne’s lace, parsley, dill), and mints (sage, thyme, oregano, lavender, rosemary).
Birds, who daily consume one-third of their weight in insects, also should be welcome in the garden. Birdhouses, birdbaths and ponds will encourage their presence. Hibiscus, trumpet and tubular flowers attract hummingbirds.
Any plant, improperly sited, where light is scarce and air circulation limited, is prone to attack by insect pests. If planted up against a building, abutilon becomes infested with scales. If given too much sun, boxwood and violets attract spider mites. If given insufficient light and air, citrus trees become menageries of insect pests.
There is an opinion that success in controlling insect pests depends on control of ants. Ants carry sucking insects – aphids, scales, mealy bugs, trips – onto plants. These insects cannot digest all the sugar they suck from leaves and steams; the excess is secreted and picked up by the ants. Ants also fight off beneficial insects. A sticky preparation – sold as Tanglefoot or Stickem – may be applied to tree trunks to serve as a physical barrier to ants. Around low-growing plants, any product containing boric acid will deter ants. The tansy herb (Tanacetum vulgare) also is effective. I once saw an antless peach tree where tansy had been planted around the trunk.
Sometimes, insect pests are encouraged that resist control. Several years ago, there was a severe infestation of the ash white fly in this area, finally overcome by its natural predators – parasitic wasps imported from Israel and Italy. At the time, the only remedy that offered partial relief was application of foliar fertilizer, such as Miracle-Gro, followed by deep irrigation. It was felt that this treatment invigorated the plant so that it could, in some way, outgrow the effects of the white fly, even if the insect itself remained.
Ms. E.V. Ziegler of Sylmar writes: “I have many large grubs, -1/2-inch around, in my compost pile. Is there anything I can do to eradicate them?” These grubs, which metamorphose into those noisy, metallic green June beetles eat ripe fruit, especially figs. The grubs live deep in the compost and are difficult to control, although they are more of a nuisance than a pest. Spray the adults with horticultural oil.
Tip of the week
As the leaves of bulk plants turn brown, they can be dug up, divided and replanted. If not divided every few years, the flowering of these plants – such as agapanthus, fortnight lily, iris and society garlic – will be diminished.
originally published 7/23/94