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What Are Pesticides? - Definition and Difference Between Narrow-Spectrum & Broad-Spectrum

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  • 0:06 What Are Pesticides?
  • 1:34 Narrow-Spectrum Pesticides
  • 2:27 Broad-Spectrum Pesticides
  • 4:19 Lesson Summary
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Lesson Transcript
Instructor: Margaret Cunningham

Margaret has taught many Biology and Environmental Science courses and has Master's degrees in Environmental Science and Education.

The crops and livestock we use for food are constantly at risk of harm from pests. This lesson will explore the methods for managing agricultural pests, including both narrow- and broad-spectrum pesticides.

What Are Pesticides?

Have you ever been annoyed by a sibling or friend? Often, people refer to someone that bothers them as a pest. In the agricultural world, there are pests of another kind, and they are any unwanted organisms that feed on or harm agricultural crops, ornamental plants or livestock. Pests can often cause harm to livestock or crops by consuming them or using up vital nutrients. To prevent damage, farmers utilize specific methods to remove or eliminate pest problems. Pesticides, chemicals that kill or manage the population of pests, are the main combat method used.

Due to the fact that there are many different types of agricultural pests, there are also many different types of pesticides. Pesticides are often divided into several different categories, including insecticides, fungicides, rodenticides and herbicides. Insecticides are used to kill unwanted insects, and rodenticides are designed to kill rodents, such as rats and mice. Fungicides are used to kill fungal pests, and herbicides are used to kill unwanted plants, commonly referred to as weeds.

In addition to pesticides being characterized by the type of organisms they manage, they are also often divided by their range of coverage. Pesticides can be either narrow-spectrum or broad-spectrum, based on the size of the range of organisms they influence.

Narrow-Spectrum Pesticides

Pesticides that have a small coverage range are referred to as narrow-spectrum pesticides, because they are designed to kill or manage a select group of organisms. Narrow-spectrum pesticides make it possible to target a specific species or group of organisms that are known to cause damage. Many narrow-spectrum pesticides are designed to interact with a characteristic of the pest that is specific to that organism, such as a pheromone, hormone or physical feature.

An example of a narrow-spectrum pesticide is chitin inhibitors, which are chemicals that interact with chitin, a component of the exoskeleton of insects. This pesticide inhibits the development of chitin and will eventually result in the death of the insect. The chitin inhibiting pesticide will only harm insects that have chitin in their exoskeletons and will not affect other insects.

Broad-Spectrum Pesticides

Although sometimes it is desirable to target a specific species or group of organisms, in some situations, it is necessary to eliminate a wider range of pests that are causing harm. Broad-spectrum pesticides are pesticides that are designed to kill or manage a wide variety of organisms.

Broad-spectrum pesticides are used when many different species of organisms are causing harm or when the specific organism causing harm is unknown. In order to kill or manage such a large variety of organisms, most broad-spectrum pesticides are designed to target a system that is common in many organisms, such as the nervous system or muscular system.

An example of a broad-spectrum pesticide is methyl bromide, which is designed to control pests ranging from small insects and pathogens to larger weeds and rodents. The pesticide can be injected into the ground to kill organisms in the soil that might harm the plant while it is growing. It can also be pumped into warehouses or barns to kill pests that could harm the plant during storage or transport for sale.

Although broad-spectrum pesticides can be effective because they can eliminate all possible pests, they can also have undesired effects. When using broad-spectrum pesticides, the chemical can harm both pests and non-pest organisms.

In particular, some insecticides cause harm to all insects, and although they kill the harmful insects, they also kill beneficial insects, such as pollinators. Pollinators are organisms that facilitate plant fertilization by transferring pollen, and some common pollinators include bees and butterflies. If the pesticide kills pollinators, the crop will suffer, because the mechanisms for fertilizing the plant will no longer exist.

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