Finding the Culprit
If you think a garden consists mostly of plants, think again. A closer look reveals that the plants are outnumbered by insect armies co-existing in the same little patch of land.
Not all bugs are harmful. Some eat mold and decaying matter; others pollinate. But there are many bugs that feed on a plant’s tissues and life-giving sap. Sometimes affected plants need help fending them off.
However, blasting away with the most lethal insecticide available will only make the problem worse. Broad-spectrum insecticides also wipe out insects that prey on the bugs you want to get rid of. Before resorting to the big guns, try some of the methods listed below. If you must use chemicals, make sure you have correctly identified the pest, and ask a nursery worker to help you select the product most effective against it.
GIANT WHITEFLIES
What to look for: Filaments of white, waxy honeydew that they excrete on leaves that turns to sooty mold. Giant whiteflies look like tiny white moths and typically fly out when plant is shaken or sprayed. They weaken plant by feeding on its sap. Heavy infestations will cause plants to defoliate and die.
Commonly found on: Hibiscus, bird of paradise, eucalyptus, lantana, bougainvillea, ficus, xylosma, gardenia, camellia.
Season: Year-round but abundant in warm months.
What to do: Spray undersides and tops of leaves once week with strong blast of water. Remove affected leaves from plant and place in plastic bag for disposal. If problems persist, spray with insecticidal soap, neem oil or other horticultural oil once a week for three weeks. Whiteflies have few natural predators, and most insecticides are ineffective against them.
TOBACCO BUDWORMS
What to look for: Irregular holes in petals and leaves, damaged buds and fewer flowers. Tobacco budworms are rarely visible because they feed only at night and take on the color of the plant material they are digesting.
Commonly found on: Petunia, geranium, impatien, begonia.
Season: Summer/fall.
Controls: Pick off affected leaves and petals. Spray weekly for three weeks with bacillus thuringiensus.
APHIDS
What to look for: Large groups feeding on flowers and leaves. Aphids suck sap from tender new growth, causing leaves to yellow and wilt, flowers to become deformed. The honeydew they excrete turns to sooty mold.
Commonly found on: Roses, pyracantha, photina, fruit trees.
Season: Year-round, abundant in spring.
What to do: Smash with fingers, spray plant regularly with strong blasts of water. Spray with systemic insecticide, horticultural oil, or insecticidal soap.
SPIDER MITES
What to look for: Leaves at bottom of bush turn yellow, feel sandy and have a silvery webbing underneath. Leaves turn brown and drop.
Commonly found on: Roses, marigolds, other bedding plants.
Season: Summer and fall; thrives in hot and dry conditions.
What to do: Spray undersides of leaves with strong blast of water. Spray neem oil, Avid or other miticide. Water regularly; do not allow plants to dry out.
THRIPS
What to look for: Withering buds and brown streaks on petals of buds that open. Damage typically more noticeable on light-colored flowers. They feed on the buds’ sap and make small slits to lay eggs.
Commonly found on: Rose, iris, day lily, gladiolus.
Season: Year-round.
What to do: Spray Orthene directly into buds when they begin to unfurl.
SAWFLY LARVAE
What to look for: Bright green caterpillar-like. Skeletonize leaves by chewing holes between the veins.
Commonly found on: Azalea, rose.
Season: Summer and fall.
What to do: Pick off or spray with horticultural oil.
LEAF CUTTER BEES
What to look for: Semicircles chewed out of leaf edges.
Commonly found on: Green ash, lilac, Virginia creeper, rose.
Season: Late summer, early fall.
What to do: It’s best not to bother these insects, which are vital in pollinating wildflowers and certain crops. The damage is mostly cosmetic, and anyway, systemic insecticides are ineffective because bees use the leaf sections to build their nests and do not eat them.
Key:
* Bacillus thuringiensus: A beneficial bacteria that invades the digestive tracts of caterpillars and worms.
* Horticultural oils, insecticidal soaps: Less toxic than chemical insecticides. Clogs insect’s breathing apparatus, coats its legs and wings. Effective on aphids and whiteflies. Won’t kill larger insects such as bees and lady bugs but will kill ladybug larvae. Oils include Ultra Fine, Sun Spray, Rose Defense and Bio Neem. Soaps are available commercially or mix a mild version using one tablespoon liquid dish detergent per gallon of water.
* Insecticides: Some must be sprayed directly on the insect to be effective. Others are absorbed into the plant’s system, making it toxic to pests. Read the label and follow directions carefully. Insects can mutate into pesticide resistant strains if exposed to the same chemical repeatedly. As a prevention, rotate between two or three brands.
Information
Web sites devoted to insect identification and integrated pest management methods:
* Baldo “Bugman” Villegas’ Bugs and Roses Home Page
Baldo is an entomologist with the California Department of Food and Agriculture. He loves to share his knowledge, and if you can’t find what you need on his site, you can e-mail him with your questions.
https://www.jps.net/rosebug/index.html
* Symbio’s Nontoxic Pest Management Page
Extensive bug identification resources. Practical advice.
https://www.symbio-witticism-page.com
Sources: Baldo Villegas; Gary Matsuoka, Laguna Hills Nursery; Ray Sturgess, Greenthumb International.
Graphics reporting by JANICE JONES DODDS, Los Angeles Times
