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Down the Garden Path

Pesticides – What are They?

Pesticides are used every day, but many people are not aware of their properties and that they may even be using them. A pesticide is any chemical (synthetic or natural) that is used to repel, control or kill a pest; this might be weeds, pathogens that cause plant diseases, insects or rodents.

The word pesticide represents a wide variety of natural and synthetic products that also are known by more specific wording, depending on what is being managed. Insecticides are for the management of insects and other related creatures. Herbicides control weeds; fungicides are used to control fungal causing diseases; and rodenticides are used for mice, rats and other rodents. If you need to control slugs and snails, then it is a molluscicide.

We use them every day routinely without giving them much thought. When you sanitize your countertops before preparing a meal, you are using a pesticide because you are killing pathogens that can make us sick. If you get a bacterial infection, you go to the doctor and get a shot. Ant baits work because there is an insecticide in the bait that the ants carry back to the nest. Using a bleach product to clean the bathroom is another example.

Outside our pests are often weeds in the landscape or flowerbeds. Using a pre-emergence crabgrass control product kills the crabgrass seed before it even sprouts. Corn gluten does the same thing in an organic form.

Some insecticides work as a contact material, others when the insect feeds on the plant. Herbicides work on weeds preventatively, like the crabgrass products, others when sprayed directly and yet others when the chemical is absorbed and moved throughout the weed. Plant disease pathogens are managed by preventing the disease from establishing on the host plant. Fungicides applied to the plant control the spores before they can invade any plant tissue.

Gardeners and homeowners should take a great deal of care when using any pesticide and cleaning or sanitizing products. There are plenty of precautionary and warning statements on these kinds of products that need to be read before using them. Finding a skull-and-crossbones symbol on any product will let you know you have some very dangerous material in your home or garden shed. Cleaning products often have a statement that says do not use in a confined area because inhaling the fumes can make us sick or worse. Pesticide labels will let you know what you should be wearing while mixing and spraying.

There are other signal words on pesticide containers relating how toxic the product may be.

Toxicity category

Signal word










None required

These signal words relate to how much or how little of the pesticide it would take to cause illness or death if ingested. This can range from just two or three drops to a teaspoon to as much as a pint or more. These amounts are based on an average sized adult of 160 pounds. It takes far less for children to become ill.

The best way to handle pesticides and sanitizing cleaning products is to read, understand and follow all the safety information on the container.

Richard Hentschel is a Horticulture Extension Educator with University of Illinois Extension, serving DuPage, Kane and Kendall counties. Stay tuned to more garden and yard updates with "Down the Garden Path" at and the "Green Side Up" podcast at