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Low impact insecticides for gardeners

Now that we have left the doldrums of winter behind us, the promise of a new growing season beckons. Although we hope we don't encounter insect pests, we should be prepared to act if it becomes necessary. When using integrated pest management (IPM), we explore any non-chemical methods that could be effective first. However, there may be times when some of us need to consider applying an insecticide in our garden or yard.

The following is a list of common garden and yard insecticides that homeowners may find in stores. This is not a list of every insecticide available to home gardeners, but includes many of the low-impact and most common active ingredients. The listing of any specific trade names is not meant as an endorsement of these products but to just point out examples of pesticides with a particular active ingredient.

When examining product labels, look carefully for the active ingredient, which is often in small lettering. Examine product labels carefully to be sure the plant you wish to treat is listed on it and the product is used correctly.

• Bacillus thuringiensis (B.t.) variety kurstaki is a naturally occurring bacterial disease of insects. It is specific to caterpillars (butterfly and moth larvae). It is a stomach poison, killing insects after they have consumed it. It is most effective against young larvae. Examples include Bonide Bacillus Thuringiensis (BT), Hi-Yield Dipel Dust, and Green Light Dipel Dust.

• Horticulture oils are either derived from petroleum oil, plant oils (typically derived from the seeds), or even fish oils. Oils are used to suffocate certain insect and mite eggs. It can also suffocate certain immature and adult insects, especially soft-bodied ones like aphids and scale crawlers, as well as mites. Examples include Bonide Mite-X (cottonseed oil, clove oil, garlic extract) and Ortho Volck oil spray (petroleum oil).

• The active ingredient of insecticidal soap is listed as potassium salts of fatty acids. They are generally effective against small, soft-bodied insects, such as aphids. They are usually believed to affect insects by penetrating and disrupting the cell membranes. Examples include Bonide Insecticidal Soap, Natural Guard Insecticidal Soap, and Garden Safe Insecticidal Soap.

• Neem and Neem Derivatives are derived from the neem tree, a plant found in arid tropical and subtropical areas. There are many compounds that can be synthesized from neem and different extraction methods can produce different products. Neem products are generally divided into one of three groups: azadirachtin-based products, neem oil-based products, and neem oil soap products.

Neem can deter insect pests by inhibiting their feeding, repelling them, or disrupting their life cycle by preventing them from successfully molting. Neem is generally effective against a wide array of insects, such as aphids, caterpillars, beetles, leafminers, and thrips. Examples include Green Light Fruit Tree Spray and Green Light Neem II.

• Pyrethrins are made from the ground flower blossoms of the chrysanthemum plant, especially Chrysanthemum cinerariaefolium. It is a fast-acting contact insecticide that affects the nervous system, paralyzing the insect. Some products may be mixed with a synergist, that is, a product that makes the pyrethrins more effective, although by itself it does not have any insecticidal properties. This insecticide is effective against a wide spectrum of insects. Examples include Bonide Japanese Beetle Killer and Garden Safe® Brand Rose & Flower Insect Killer.

• Spinosad is produced by the fermentation of a soil-dwelling bacterium, Saccharopolysora spinosa. It is quick acting, attacking the nervous system of insects. It is most effective against caterpillars, flies (mostly leafminers), and thrips and is also reasonably effective against leaf beetles and grasshoppers and similar insects that consume a lot of foliage. Examples include Garden's Alive Bulls-EyeTM, Bonide Captain Jack's Deadbug Brew, and Green Light Lawn and Garden Spray.

For additional insecticide options, view the Yard & Garden News on the University of Minnesota Extension website at Look for the article titled 'A Brief Survey of Insecticides Available to Minnesota Gardeners' in the April issue.

For more information, contact me at the Polk County Extension office in McIntosh or at the Clearwater County Extension office on Wednesdays. Our toll free number is 800-450-2465, if e-mail is your thing, contact me at

Source: Dr. Jeffrey Hahn, Entomologist, University of Minnesota Extension.