In The Garden: Make Nature Your Ally in Combating Garden Pests

By | May 01, 2012
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Stamp Album
Illustration from the Album Timbres (Stamp Album) of Chocolats Peter, Cailler’s Kohler, Nestlé, circa 1930.

Critical in our thinking about ridding the garden of pests is to also accept them. This is a fact of life that we too often deny, slathering pesticides on our home-grown food because we are afraid of a few holes or too fastidious to cut out the bad spot. Large vegetable operations do not have the same luxury that the backyard gardener has; we can monitor, pick, squish, spot treat or ignore with no financial risk.

We also can employ a range of products that include botanical and biological pesticides that offer some protection without using synthetic chemicals.

The Environmental Protection Agency categorizes biopesticides in several classes: those that are sourced from plants, animals and certain minerals, and naturally occurring bacteria, virus or protozoa. The agency also recognizes “incorporated protectants,” which is another way to describe genetically modified plants that have had the gene of a biopesticide inserted into it so it can manufacture its own protection. We will focus on the former, not the latter, and I will remain old school in my terminology and refer to our pest control options in terms of botanicals (derived from plants) and biological (derived from microbials such as bacteria).

Sesame oil, cedar oil, thyme oil, clove oil and neem oil are botanical oils that work in several different ways: Some repel because of their strong scent; some smother; others are ingested and disrupt the physiology of the offending insects; and some act as a barrier against fungal spores, thus preventing some fungal diseases.

The blends of plant oils like clove, thyme and sesame oils are easy options when it comes to controlling pests on food crops. These oils are already FDA-approved food additives so they can be used in the vegetable garden up to the day of harvest. The spicy oils repel or spell major stomach upset for many insect pests. An insect with no appetite is uninterested in our plants and eventually starves to death.

Insecticidal soaps are derived from fatty acids from potassium in most cases and are a reliable standby against many of the soft-bodied pests that may be present among our house plants, including aphids, mealy bugs, fungus gnats and whiteflies. Pyrethrin is another old standby for the organic gardener that is derived from chrysanthemums. It works on a wide range of insect pests in the garden but care must be taken not to use it around aquatic life because it can be toxic to fish.

Whole neem oil is an excellent organic pesticide that works on a whole range of pest problems including black spot, rust, mildew, mites and insects. It comes from the seeds and fruit of an evergreen tree. Whole neem oil is a broad-spectrum botanical pesticide, however, and will not discern between the good bugs and the bad bugs.

Neem oil extracts (note the difference between the two: one is whole oil, while the other is an extract) are more widely available under a variety of trade names. Just refer to the active ingredient listing on the package. Extracts, unlike the whole neem oil, will effectively control insect damage by suppressing the insects’ desire to eat your plants and by stopping larval development. Research suggests that the predominant compound found in the neem tree, azadirachtin, can also cause sterilization, act as a growth regulator and impact the pests over all “biological fitness.” A 90% neem oil extract on the active ingredient label is what you want for efficacy on adult-stage pests. Neem is also used in personal care items like soap and toothpaste.

Bt, or Bacillus thuringiensis, is a naturally occurring soil bacterium that proves to be most effective on caterpillars, especially in the early stage. The pest must ingest the Bt, which disrupts the gut, acting as an appetite suppressant so the caterpillar stops eating and dies.

Another product that is also a naturally occurring soil bacterium is Spinosad. The story behind Spinosad is funny: A scientist on vacation in the Caribbean took a soil sample from an abandoned rum factory floor and discovered a fermented soil bacterium (which has never been found anywhere else since) recognized as a new species that they named Saccharopoly spora, now referred to as Spinosad.

If a caterpillar ingests Spinosad it over-stimulates the nervous system resulting in death. Spinosad, Bt, neem and pyrethrin all have minimal impact on beneficial insects like bees, earthworms, ladybugs and hover flies.

When it is all said and done, though, remember that even if a treatment is considered “least toxic” it still has the potential to do some damage if not used properly. There is always the risk of burning foliage if products are applied during the heat of the day, especially if temperatures are over 90. Treat in the early morning or evening hours and always follow the directions for rate, time and frequency of application for the desired result.

Do not be tempted to overuse just because of a feel-good label of “botanical” and “biological.” Sometimes picking Colorado potato beetles off and dropping them in a bucket of water is all the pest control you need.


Controls both insect and fungal pests including mites, aphids, bed bugs, scale, leaf miners, caterpillars, beetles and squash bugs among many others; and as a fungicide it controls black spot, rust, powdery mildew and scab.


Controls most leaf-eating pests in the caterpillar stage of life including bagworms and tent caterpillars; as well as borers, Colorado potato beetle, Japanese beetles (among other beetles), leaf miners, loopers and spider mites.

Bacillus thuringiensis (Bt)

Controls most leaf-eating pest in the caterpillar stage and will not harm beneficial insects. Also controls cabbage worms, loopers, leaf rollers and leaf miners, horn worms and more. Bt-i (israeliensis strain) “donuts” are sold to put in water to kill mosquito larva, as well.


Controls many pests including asparagus beetles, aphids, cabbage loopers, cabbage worms, cucumber beetles, flea beetles, leaf hoppers, potato beetles, stink bugs and white flies. Be mindful of label instructions and do not apply around fish.

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