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Pests in Gardens and Landscapes: Quick Tips

Bt products.

Insecticides are substances applied to control, prevent, or repel insects. Insecticides can be an important part of integrated pest management programs; however, some products can worsen pest problems or harm people or wildlife. Other products—often called less toxic pesticides—cause few injuries to people and organisms other than the target pest. The less toxic insecticides listed below should be a first choice when you need pesticides to control insects. Always check product labels to be sure the pesticide is registered for your plant or pest situation.

Soaps (potassium salts of fatty acids):

Insecticidal soaps control aphids, whiteflies, and mites; come in easy-to-use squirt bottles for small jobs; and require complete coverage of pests and sometimes a repeat application.

Insecticidal oils:

Oils control aphids, whiteflies, mealybugs, scale insects, spider mites, lacebugs, psyllids, and thrips. Good coverage of plants is required. Don’t apply to water-stressed plants or when temperatures are above 90°F. Petroleum-based oil products include superior, supreme, narrow range, and horticultural oils. Plant-based oil products include neem and canola oils.

Microbial insecticides:

Microbials are derived from microorganisms that cause disease only in specific insects:

• Bacillus thuringiensis (Bt) subspecies kurstaki (Btk) controls leaf-feeding caterpillars. Bt subspecies israelensis (Bti), sold as mosquito dunks, plunks, and bits, controls mosquitoes and fungus gnats.
• Codling moth granulosis virus (Cyd-X) controls codling moth.
• Spinosad is a microbial-based insecticide that controls caterpillars, leafminers, and thrips, but it can also harm some beneficial insects.

Beneficial nematodes:

Entomopathogenic nematodes are microscopic worms, mostly Steinernema and Heterorhabditis species, that attack and kill lawn insects, clearwing moths, and carpenterworm. Because nematodes are living organisms, they are very perishable, so order through the mail to assure freshness.

Botanical insecticides:

Derived directly from plant materials, botanicals vary greatly in their chemical composition and toxicity but usually break down in the environment rapidly.

• Pyrethrins (pyrethrum) are used against a range of insects but are toxic to fish and aquatic organisms.
• Azadirachtin, from the neem tree, has limited effectiveness against pests but low toxicity to nontargets. Don’t confuse with neem oil.
• Garlic, hot pepper, peppermint oil, and clove oil are sold as insect repellents that protect plants. Limited information is available regarding effectiveness.

Avoid these more toxic pesticides:

• Pyrethroids such as permethrin, cyfluthrin, cypermethrin, and bifenthrin move into waterways and kill aquatic organisms.
• Organophosphates such as malathion, disulfoton, and acephate are toxic to natural enemies.
• Carbaryl harms bees, natural enemies, and earthworms.
• Imidacloprid is a systemic insecticide that can be very toxic to bees and parasitic wasps, especially when applied to flowering plants.
• Metaldehyde, a common snail bait, is toxic to dogs and wildlife. Use iron phosphate baits instead.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.