Learn about organic pest control products when cultural controls cannot keep garden pests at bay.
Cabbageworms can be treated with “Bacillus thuringiensis,” also known as Bt.
PHOTO: DWIGHT KUHN
There is no such thing as a one-size-fits-all organic remedy for destructive insects. Instead, you should tailor your plan of attack to the pest itself, while also considering potential risks to beneficial insects and other wildlife. Or, you can choose to do nothing at all. In the vegetable garden, light insect feeding causes little or no loss of productivity, and having a few pest species present helps to support populations of beneficial insects. The pests below are grouped according to control measures that are known to work well.
Cabbageworms, mosquito larvae, army worms, tomato hornworms and other leaf-eating caterpillars
Organic Pest Control Products: Products made from naturally occurring Bacillus thuringiensis, often abbreviated as Bt, such as Dipel Dust and Gnatrol. After the insects eat the bacteria, their guts rupture and they die. It’s important to note that sunlight degrades Bt after a few hours. Some Bt products include genetically modified strains; products listed by the Organic Materials Review Institute (OMRI) include only naturally occurring forms.
Aphids (except green peach aphid), mealybugs
Organic Pest Control Products: Insecticidal soap, such as Safer Insect Killing Soap, which breaks down the pests’ protective cuticles so they quickly become dehydrated. Repeat applications may be needed, and leaf tissues of some plants may be damaged, especially in very hot weather.
Organic Pest Control Products: Light horticultural oils, such as Concern Pesticide Spray Oil (plant-based) or SeaCide (fish-based). When applied directly to pests, these oils interfere with respiration, causing insects to suffocate and die. These oils also can kill beneficial mites and cause leaf injury to some plants.
Squash bugs, leafhoppers, cabbage root maggots, onion root maggots
Organic Pest Control Products: Products based on extracts from neem trees, such as Safer 3 in 1 Garden Spray and Green Light Neem Concentrate. Neem extract interferes with molting, reduces feeding and causes some insects to stop laying eggs. Apply when pest insects are young and repeat applications every few days.
Colorado potato beetles, Mexican bean beetles, thrips, fire ants
Organic Pest Control Products: Products based on spinosad, such as Monterey Garden Insect Spray and Conserve, are made from naturally occurring bacteria found in some Caribbean soils. Spinosad causes susceptible insects to have convulsions until they die of exhaustion. This substance is toxic to honeybees and other beneficial insects, so treated plants should be covered to exclude accidental casualties. Fire ant baits containing spinosad (such as Fire Ant Control with Conserve and Safer Fire Ant Granular Bait) are effective when used according to directions.
Flea beetles, tarnished plant bugs, green peach aphids, potato aphids
Organic Pest Control Products: Products based on all-natural pyrethrum (not synthetic pyrethroids), such as Safer Yard and Garden Insect Killer and PyGanic. Pyrethrum causes immediate paralysis in many pest insects, and it will do the same to beneficial insects. It also is toxic to fish and some birds, so it should be used with care and only as a last resort.
Roaches, ants, silverfish
Organic Pest Control Products: Products made from boric acid, a naturally occurring mineral, or those made from diatomaceous earth (DE), a powder made from fossilized prehistoric crustaceans called diatoms. Boric acid is a stomach poison, and you can buy ready-to-use boric acid baits, such as Safer Roach and Ant Killing Powder. The sharp edges of DE cut into insects’ bodies, causing them to die of dehydration. In the first few days after their habitat is treated, cockroaches may become more visible as they desperately search for water, but will die within two weeks. DE becomes less effective when wet, and prolonged exposure can cause lung irritation in people and pets. The best way to use DE indoors is to put it in cabinets and wall crevices.
Read more: Before turning to chemicals, read about alternative pest control techniques in Organic Pest Control Strategies for the Garden.
Contributing editor Barbara Pleasant gardens in southwest Virginia, where she grows vegetables, herbs, fruits, flowers and a few lucky chickens. Contact Barbara by visiting her website or finding her on Google+.
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