You can find pictures, details and treatment options for most damaging insects at the University of California Integrated Pest Management website http://ipm.ucanr.edu/index.html.

Below is a brief description of the most common insects:

Aphids

One of the most common insects comes in many colors and shapes. They deform leaves and will spread diseases. Encourage natural predators. If necessary, spray with soapy water or horticultural oil or blast of water.

Snails and slugs

One of the most destructive pests. Control by clearing areas where they can hide. Hand pick when possible. Snail baits using iron phosphate are usually safer and many are organic.

Grasshoppers

The garden provides the Nolo bait which contains natural occurring spores that causes grasshoppers to become lethargic and die. Effectiveness is questionable in our area. Hand catch is another option.

Whiteflies

Tiny and abundant sap sucking insects. Encourage natural predators. If necessary, spray with soapy water or horticultural oil or blast of water.

Sowbugs and pillbugs

Not insects. They feed on decayed plant matter and are important decomposers. They can sometimes feed on young plant stems, killing them. Keep compost away from young stems. Keep area dry around plant by watering early in the day. Keep leaves and fruit off the ground.

Flea beetles

Commonly found on eggplants. They make many tiny holes and can severely damage plants. Control with spinosad.

Root knot nematodes

Microscopic, eel-like roundworms feed on plant roots leaving galls on root ends. Plant growth slows down, leaves turn yellow and wilt under heat. Common mistake made by gardeners is to add more water and fertilizer when symptoms appear which may cause additional damage. Remove infected plants. Control by plant rotation, cultural practices. Azadirachtin may slow damage.

Tomato russet mite

Tiny insects are noticed when lower leaves and stems become bronze or russet colored. Cause extensive damage if not treated early. Remove infected leaves then spray with sulfur.

Corn earworm/Tomato fruitworm/Cabbageworm

Watch for eggs on corn silk when it first emerges. Cabbageworms create many small irregular holes in leaves. Many natural predators including parasitic wasps attack eggs. Can be suppressed by spinosad or Bacillus thuringiensis (BT) when detected early. BT is less harmful to predators but must be applied at the right time. Consider purchasing Trichogramma parasites with your garden neighbors. Covering crops with tulle fabric can also be effective.

Hornworms

These are large green worms that cause extensive damage to tomatoes and other crops. Same treatment options as other worms.

Fig beetle

Bright green beetles emerge in early to mid-summer and feast on fruit. No chemical treatments recommended but you can easily make homemade traps found on many websites. Do not purchase treatments for Japanese beetles as these have no effect on the fig beetle.

Buffalo treehopper

Green, triangle shaped, less than half inch in size they suck juice out of herbaceous or woody plants. Nymphs are reddish brown with numerous spines. Can usually be picked off by hand. Can be controlled by insecticidal soap or horticultural oil if found in great numbers.

In order to attract beneficial insect, it is important to understand the role of Argentine ants in your garden.  Many damaging insects such as aphids, mealybugs, scale produce a sweet substance called “honeydew” which the ants like.  In return, the ants protect them from their enemies and often move them to new locations to increase their populations.  Controlling ants in your garden will usually solve many if not most of your insect problems.

You can encourage beneficial insects into your garden by planting flowers such as alyssum, yarrow, cilantro, cosmos, marigold, dill and thyme.

Source:
http://ipm.ucanr.edu/QT/beneficialpredatorscard.html
https://cisr.ucr.edu/invasive-species/argentine-ant

Argentine ants are among the most destructive insects in your garden.  They protect insects that damage your plants and spread diseases such as cucumber mosaic virus.

First, locate their nests which are usually under hard objects such as boards or bricks.  Water, even just a small amount, causes them to flush out of their nest with eggs.  Spray them with a safe insecticide.

Permethrin (synthetic) or pyrethrin (organic) are very effective and have residual protection.  But these insecticides are harmful to many beneficial insects.  Only use them on the ground and not on plants.  Soapy water is somewhat effective but doesn’t have any residual protection.  Let as many ants come out as possible before spraying.

Ant bait stations can be helpful.  You can purchase these at most garden stores or make your own borate-based bait.

Source:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html

Below are some of the most common garden insecticides listed with least to most damaging effect on beneficial insects.  Be sure to read the EPA label and follow all directions.  Whenever possible, consider biological controls first.  More detailed information can be found at the National Pesticide Information Center and UC IPM.

Blast of water

A good blast of water can knock off many damaging insects and interfere with mating.  Best done in the morning to let plants dry before night.

Soapy water, insecticidal soaps

Many recipes can be found online or you can purchase concentrates.  Kills aphids, mealybugs, thrips, spider mites, scale, whiteflies, ants and other soft bodied insects.  Affects some beneficial insects.  Damages plants if used in heat of day.  No residual protection.  Can be washed off in a half hour.

Bacillus thuringiensis (BT)

Organic biological control for caterpillars.  Low impact on beneficial insects.  Timing of application critical for control.

Spinosad

Active ingredient is organic but some formulations are not.  Controls caterpillars, mites, thrips, flea beetles. Use early or late in day to protect bees.  Some residual protection.   Low to moderate impact on beneficial insects.

Sulfur

Controls many types of mites.  Low to high impact on beneficials.  Incompatible with horticultural oils.  Can damage lungs if dust is inhaled.

Horticultural oil, Neem oil,Azadirachtin

Controls mites, aphids, mealybugs, scale.  Low to moderate impact on beneficials.  May damage leaves if applied in the heat of day.  Incompatible with sulfur applications.  Azadirachtin can be used as a soil drench to control root knot nematodes.

Permethrin, Pyrethrin

Pyrethrin is organic.  Controls most types of insects.  Very damaging on beneficial insects, bees.  Effective treatment for ants and termites with residual protection.  Avoid using on edible plants or in places where beneficial insects are likely to inhabit.

These businesses can assist you in deciding which beneficial insects will help with your bug problems and when they can be effectively applied.  You might want to work with your garden neighbors and share the costs.

Biotactics Inc.
Menifee, CA
Phone 951-943-2819
https://benemite.com/

Evergreen Growers Supply
Clackamas, OR
Phone 503-908-1946
https://www.evergreengrowers.com/

Arbico Organic
Oro Valley, AZ
Phone 800-827-2847
https://www.arbico-organics.com/