Understanding Biopesticides And How To Use Them Safely


Japanese beetle

The word biopesticide can provoke strong reactions these days, immediately conjuring up images of people spraying toxic chemicals that are hazardous to human health. Complicating matters is the fact that just because a pesticide says it’s organic doesn’t mean it isn’t toxic. Still, sometimes a gardener has no choice but to reach for a biopesticide or other, more conventional product, to save plants from immediate destruction. That’s why the best approach is always to understand your pesticide before you spray.

There are many multi-purpose pesticides around promising to treat molds, mildew, insects and disease all at once. I’d equate these to shampoos with conditioners; do all-in-one products ever really work that well? In the garden, the best strategy is to choose products specifically targeted to the problem at hand and to use them sparingly, opting for the least invasive approach first and choosing alternatives to chemical pesticides whenever possible.

What is a pest?

Insects, disease causing organisms, weeds, birds and other mammals are all potential pests in the garden. These organisms compete with humans and desired plants for sun, food and water. Good pest management starts with learning to identify the damage each of these groups produce and then choosing the least invasive methods for control.


Eastern Swallowtail caterpillar on parsley

Three types of control: Prevention, Suppression and Eradication 

Sometimes simply buying the right plant for the right location can prevent a whole host of problems. Other times, eliminating some of the pests by suppressing their proliferation at the right time in their life cycle is treatment enough. Then, there are those problems that are so deeply-rooted, you’ll need to pull out the heavy guns and go for complete eradication.

Integrated Pest Management (IPM) can improve the success rate of pest controls while reducing risks to humans, other animals and the environment. It all starts with being able to identify the good and bad insects in your landscape. Many insects are actually beneficial to the garden, where they act as natural pest controls. When treating a problem, it’s important not to eliminate them, too.


Ladybugs are beneficial insects

Get to know the characteristics of the damage different pests produce and under which of the above categories of control the problem falls. Is the pest an insect, weed, disease or abiotic (non-living ) problem? Sometimes you don’t have to eliminate an entire population to get things under control. This is called knowing the action threshold; or understanding the level at which pest populations have gotten so large that they pose injury or harm to the garden.


Squash beetles are invasive

Never reach for a pesticide product without first doing your research. Once you’ve identified the problem, choose carefully to ensure the product you select is designed for the job. Here’s a breakdown of some of the naturally-occurring options available today.

Biopesticides (biological pesticides) are slow-acting pesticides derived from natural materials such as bacteria and other microbes, fungi, algae, nematodes, proteins and certain minerals. They are designed to target a single or small number of closely related insect species as well as to control some types of disease.

Rather than eliminate a pest completely, biopesticides suppress it, without harming beneficial insects or altering basic aspects of a plant’s physiology. Biopesticides are also biodegradable, which means they have a lower persistence in the environment.


Fungi can act as a natural pesticide

Since biopesticides have a narrow target range, they must be applied at specific times to be effective. Major categories of biopesticides include miticides, avicides, insecticides, herbicides, fungicides, rodenticides, molluscicides and bactericides as well as some plant growth regulators. While these type of pesticides are ‘natural,’ they are also controversial, with some being blamed for reducing populations of bees, butterflies and other pollinators.

Microbial insecticides are a kind of biopesticide made from naturally occurring single cell organisms such as bacteria, fungi, protozoa and viruses. Environmentally compatible, they have been mass-produced and formulated to kill pest insect populations while not harming beneficial organisms. As an insecticide, they work against specific pests by infecting and exterminating them.

imgresOne of the first microbial insecticides ever registered in the United States was milky spore disease. Milky spore is a naturally occurring bacterium that uses spores to attack the larvae of certain pests, most notably the white grubs of Japanese beetles.


imgres-1The most widely used organic pesticide today is the bacterium, Bacillus thuringiensis , otherwise known as Bt. Accounting for 90 % of the organic pest control market, Bt is made from a naturally-occurring compound found in soil that is toxic to several species of insects. Reproducing quickly by spores that are ingested by the target insect, it invades the cells of the insect’s stomach where it then proliferates in its body. When applied to foliage at early larval stages, Bt can successfully eradicate most caterpillar species, larvae of flies such as fungus gnats and the larvae of some beetles.

Bt has been engineered into many GMO crops to make them disease and insect resistant as well. It remains highly controversial, however, with some studies suggesting it may be toxic to animals that feed on plants treated with the pesticide.

Plant-incorporate protectants (PIPs) are pesticidal substances that have genetic materials from other species incorporated into their own genetic materials. Although these products are controversial, many corn growers use them. In some instances, genes for specific Bt pesticidal proteins have been introduced into plants’ genetic materials and then manufactured to control the pest when it feeds on the plant. In these products, both the protein and its genetic materials are regulated by the EPA.

A word on synthetic (chemical) pesticides

Unlike biopesticides, synthetic pesticides are made from a poisonous chemical or mixture of chemicals intended to prevent, repel or kill a pest. Many pesticides are used to kill weeds, fungi and insects. The most well known example of a synthetic pesticide is DDT, which was used to control malaria during World War II and then used widely in the 1940’s and ’50’s in urban areas to control mosquitos, gypsy moths, Japanese beetles and other insects.


Most of us are aware that DDT was banned in the U.S. (in 1972) due to widespread resistance from overuse as well as mounting evidence that the chemical was leading to preterm births. Although it is now banned in many countries, however, some undeveloped nations continue to use it on crops destined for U.S. and European markets.

Another synthetic pesticide called Dursban, until 2000 was the most common pesticide used in households, schools hospitals and agriculture. It, too, was banned due to unacceptable health risks. Studies found that exposure to Dursban in early life could lead to malfunction of the nervous system later on.

Other examples of synthetic pesticides include pyrethrum (which is still allowed) diazinon, carbofurna, and fenpropanthrin, all of which have been shown to have negative effects on humans as well as to be harmful to the environment.

Natural methods of control

Of course there are many natural methods of controlling garden pests, including choosing disease-resistant plant species from the very start and planting them in clean, amended soil in a suitable environment. Check your garden regularly for signs of insect and/or animal damage and treat accordingly. Many times, you can simply pluck off the offending insect or wipe off the mold rather than having to resort to more invasive sprays.


Also, make sure your garden is free of old leaves and other debris and that mulch isn’t piled up high over the roots of plants. This can provide rich, humid environments for disease and insects to thrive.

Personal Protection

While all pesticides by law must be reviewed and approved by the EPA, many of us don’t read the directions and consequently may not be applying the products properly. In addition to using insecticides only when and where the label directs, always protect yourself by wearing pesticide-resistant gear such as pants, gloves and hats. Even glasses can be important to prevent errant sprays from touching the whites of the eye where they are easily absorbed into the body.


Finally, make sure to store your pesticides away from children and pets in a safe, cool, dark place on a high shelf. Do not allow temperatures to exceed 100 degrees Fahrenheit. Store products away from any water sources like wells. And remember, under the sink is NOT a good place for storage


Leave a Reply