Insect Pests in the Home Garden

By Kim Wilson, UC Master Gardener

Integrated pest management (IPM) is a whole system-based strategy to prevent and manage pests using environmentally sound methods. This strategy provides long term solutions, manages potential problems early and gives choices to avoid unnecessary pesticide use.

First Considerations

1. Monitor your property- catch problems early.
2. Is the pest a problem for you or for the plant? Is control needed?
3. Identify pests before treatment.
   1. Is it a good bug or a bad bug.
   2. Consider pest biology, environmental needs and adjust to control and prevent.
4. Use IPM guidelines- start with the least harmful treatment first. The goal is to reduce pest numbers, not to irradicate.

IPM uses a combination of practices for long term management:

Prevention - Dispose of fallen fruit, mummified fruit, affected plant material; choose plants resistant to pests. Use fabric row covers to exclude insects.

Cultural practices - Healthy plants can better tolerate pests. Pests favor new tender plant growth and plants in poor health. Cultural control includes methods of right plant right place, appropriate irrigation, fertilizing and pruning schedules.

Physical/Mechanical - Dislodging or picking off pests into soapy water, wiping off insects and eggs, spraying off with water. Prune to remove heavily infested plant parts.

Biological controls - Encourage the presence of beneficial insects by planting favored plants such as alyssum, yarrow, scabiosa, buckwheat and other native plants. Avoid harmful pesticides, reduce dust and control ants.

Chemical controls - Use only when nonchemical controls are not working, and pest levels are intolerable. Use them in combination with non-chemical methods and choose the least toxic options. Use at proper time (most effective on immature insects) and follow label instructions for use.

Bacillus thuringiensis (Bt) - consists of bacillus bacterium and its endotoxin. Spray on leaves to manage leaf-eating caterpillars. Best used on young caterpillars. Safe for people, pets and beneficial insects and bees.

Insecticidal Soaps - work by contact only with no residual effect, toxic to soft bodied insects such as aphids, mealybugs, whiteflies, rose slugs and soft scale. Safe for bees. Beneficial insects can be affected if sprayed with soaps.

Horticultural oil/Neem oil - controls soft bodied insects and mites and has some fungicidal properties. This contact spray coats and suffocates insects also provides effective control of eggs. Oils have some effect on bees so use only in early morning or evenings when bees are not flying.

Spinosad - organic metabolic by-product of a bacterium, kills by contact and ingestion. Controls caterpillars, flies, mosquitoes, ants, leafminers and some thrips. Does not work on soft bodied insects (aphids, mealybugs, whiteflies, mites or scale). Toxic to beneficial insects and bees so do not spray when flowers are present.

Avoid- Organophosphates such as malathion, and carbaryl or pyrethroids are highly toxic to beneficial insects and should be avoided. Systemic neonicotinoids such as imidacloprid are toxic to bees and parasitic wasps especially when plants are flowering. Avoid metaldehyde snail bait which is toxic to animals.

Most Common Helpline Pests

	Aphids- Cause leaf curling, produce honeydew. Monitor to detect early, control ants, prune out, spray off with water, use garden fabric row covers, plant flowers (alyssum) for beneficial insects. Activity decreases with cold or hot weather.
	Woolly apple aphids appear as fuzzy cottony material on tree bark and growing tips. Choose resistant rootstock, use dormant oil to kill eggs, horticultural oil or soap during growing season.
	Mealybugs - Whiteflies White cottony material on stems/fruit (mealybugs), or leaves (whiteflies). Produce honeydew, attract ants. Control ants, use consistent and persistent water sprays. Insecticidal soaps or oils if needed.
	Mites – Avocado and bean plants,- peak in summer, can stress trees, cause leaf drop. Cultural care, avoid overfertilization or overwatering. Look for predatory mites. Use strong water sprays. Reduce dust.
	Scale - Control depends on scale type. Many produce honeydew so control ants. Encourage beneficial insects, dust control, prune and open up canopy if hot, well-timed oil when immature forms appear.
	Leafminer- Good cultural care, support beneficial insects, do not encourage new growth in summer to early fall, no chemical treatment warranted in home gardens unless tree is very young as mature trees can tolerate leafminer feeding.
	Thrips- Overwinter in  soil and grasses and travel to blossoms in spring. Reduce grass or weeds where pests overwinter. Avoid overwatering or heavy fertilizer. To delay fruit damage in avocados, prune in January. Prune interior of citrus canopy and reduce dust to aid beneficial insects. Chemical control is difficult as thrips are gone when damage evident.
	Caterpillars - Tomato hornworms, cabbage looper, imported cabbage worm. Monitor to catch early; employ hand removal and Bt. Use garden fabric to cover young plants.
	Grapeleaf skeletonizer - Monitor for flying adults and caterpillars on leaves, treat early using Bt or Spinosad. Wear gloves as larvae have spines that cause skin irritation.
	Sawflies (Cherry slug- Rose slug)-chew holes or skeletonize leaves. Trees will tolerate feeding. Use insecticidal soap or horticultural oil if needed.
	Leaf-footed Bugs - favor pomegranates and tomatoes.  Remove overwintering sites such as woodpiles, hollowed pomegranates and keep weedy areas mowed. Physically remove into soapy water.
	Fig Fly - Tiny fly lays eggs in green fruit. Infested fruit prematurely drops to ground. Remove, bag and dispose of all infected fruit. Critical to clean up all dropped fruit. No treatment currently available.

References

Home, Garden, Turf and Landscape Pests. UC IPM. Identify and manage pests in homes, gardens, landscapes and lawns - UC Statewide IPM Program (ucanr.edu)

Pesticides: Safe and Effective Use in the Home and Landscape. UC IPM. Pesticides: Safe and Effective Use in the Home and Landscape Guidelines--UC IPM (ucanr.edu)

Seasonal Landscape IPM Checklist. UC IPM. UC ANR Statewide IPM Program (UC IPM)