Low impact insecticides
By Matthew R. March, MNRD
Polk County Extension Agent
Managing insect pests in your garden, landscape or around the house can be very frustrating. What is more frustrating than a garden full of vegetables nearing harvest just to be destroyed in a matter of days by a pesky little insect? Insecticides should be your last option for control, and you should rely on non-chemical methods such as crop rotation. However, sometimes insect pest numbers grow to unmanageable levels and use of insecticides is justified. Any insecticide you can purchase has been proven safe if you handle and apply the insecticide in accordance with the label. However, as good environmental stewards we should always resort to using insecticides only when it is necessary and if insecticides must be utilized first selecting a low impact (least toxic) insecticide that will control your pest. Lastly, some homeowners prefer organic insecticides, but it should be noted that not all low impact insecticides are classified as organic.
Insecticide soaps and horticultural oils kill small soft-bodied arthropods like mites, aphids and scales. Horticultural oils may be called dormant oil, volck oil, summer oil or ultrafine spray oils. These products are classified as being one of the safest insecticides, however it is recommended you apply store-bought products as they are generally safer to plants than homemade versions.
Microbes such as bacteria are everywhere in the landscape from the soil to the leaves. Many of these bacteria can be harmful to insects such as Bacillus thuringiensis, Bt, and spinosad. When Bt is consumed by insects a toxin is released that destroy cells in the gut. Spinosad is a natural toxin made by soil borne bacterium that affects the nervous system of insects. Both products are generally safe for people, however spinosad can be harmful to bees and other pollinators.
Insect growth regulators are copies of natural hormones that affect the growth of insects and such, affecting growth or preventing egg-laying. They are considered harmless to people and pets and can be very effective in stopping the life cycle of certain insect pests. Insect growth regulators can be found in products to control fleas, fire ants, mosquitos and caterpillars.
Cockroach bait stations, fire ant baits, and some slug and rodent baits are considered low impact because the pest feed directly on the bait requiring very little insecticide. Plus, baits can reduce the need to use potentially more hazardous sprays.
Boric acid is good for cockroach control and can be found in some cockroach control products. Boric acid is not toxic to the touch but can be toxic in high doses if swallowed by kids or pets.
Diatomaceous earth is a very popular low impact insecticide. Diatomaceous earth is fossilized diatoms that are abrasive. Diatoms are microscopic aquatic algae. The abrasive nature of diatomaceous earth cuts the exoskeleton of insects causing insects to dry out. Diatomaceous earth works best in dry conditions.
Botanical insecticides are derived from plants that make their own insecticides. Not all botanical insecticides are low impact and some can be very toxic. Popular products include pyrethrins, neem extract, mint oils and citrus oils. Botanical insecticides break down quickly after application so they are relatively safe for many beneficial insects that are not being targeted.
Selecting an insecticide can be very confusing. To ensure that you are selecting a product that will be effective for your insect pests, always read and follow the label. And when in doubt about what insecticide to apply or its toxicity, don’t hesitate to call the extension office.
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