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Topic 6. Pests and Pest Control. What is a pest?. Every year tonnes of chemicals are used to control pest organisms that reduce plants’ ability to produce food and fibre.

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Topic 6

Topic 6

Pests and Pest Control

What is a pest

What is a pest?

Every year tonnes of chemicals are used to control pest organisms that reduce plants’ ability to produce food and fibre.

From the point of view of a farmer or forester, a pest is an organism that is causing plants to die or produce less than otherwise would.

Insects are not the only type of pest, however: Fungi, weeds, and other animals such as slugs or birds can also be pests in certain situations.

The pest problem

The Pest Problem

In natural systems, organisms have parasites, predators, or competing plants that help keep their numbers in check.

The pests that cause the most damage are insects, fungi, and weedy plants.

Weeds are thieves, they steal moisture, nutrients, space, or light from the crop. Insects usually eat some part of the plant and fungi and bacteria can cause infections, destroying parts or all of the plant.

Insects and diseases consume over 50 percent of Canada’s annual harvest. Farmers spend millions of dollars each year to control them and avoid crop losses.

Dandelion profile of a champion

Dandelion : Profile of a Champion

1. Powerful roots – They have a powerful taproot that is anchored deep in the soil. If you try to pull up a dandelion it usually breaks off near the surface, leaving most of the root in the soil. The rot can grow new leaves and flowers.

2. Broad leaves – Dandelion leaves are wide and broad and they shade out nearby plants.

3. Super Seeds – Dandelions are able to produce flowers and seeds all summer long.

4. Adaptable – Dandelions grow well in all kinds of soil, including soil that is poor in nutrients.

Chemical weapons – Dandelions release chemical agents to slow down the growth of other grass and other plants nearby.

Canola and its pests

Canola and Its Pests

Canola is popular with fungi, insects, and weeds.

Canada Thistle

Fusarium Fungus

Wild Oats

Bertha Army Worm

Blackleg Fungus

Lygus Bugs


Diamond Black moths

Flea beetles

Blister beetles



Controlling pests

Controlling Pests

Larges pests could be chased or scared away, and smaller pests could be picked off or scared away.

Crop rotation is a process where farmers grow different crops each year as a way of controlling some weeds and diseases.

Herbicides, insecticides, and fungicides controlled weeds, insects and fungi. These chemicals are easy to use, give impressive results, and were considered safe as well as inexpensive.



The pollutants from chemicals move from level to level in the food chain and get stored in the same way food energy is stored.

Some of the chemicals wash off the plants and leave residues in the soil and water. If the pesticides are not decomposed, they can stay in the environment and remain poisonous. Toxic residues have even been found in polar ice caps thousands of kilometers from the nearest source. Pesticides are often toxic to more than one organism. In most cases, beneficial organisms, which are not the target of the chemical control, also die hen pests organisms are killed.

Resistant species

Resistant Species

Scientists have discovered that, as pesticide use increases, the number of species that can withstand the effects (are resistant) is increasing as well.

The only way to target these new tougher insects is to use harsher chemicals. These higher dosages can be even more harmful.

Organic food

Organic Food

Organic food is food that has been grown without the use of chemical fertilizers and chemical pesticides. Instead, they use manure and compost to add nutrients to the soil.

They fight weeds using tilling, crop rotation, mulching, planting their crops alongside plants that discourage insects, and removing insects by hand.

Other practices include:

Sowing good quality seeds

Removing weeds before seeds mature

Cutting weeds along the property line

Cleaning the equipment well.

Organic farmers often grow a variety of crops instead of monocultures. Benefits include higher prices for produce, increased safety for the farmer, and less chance to residue buildup.

Biological control

Biological control

Biological control means using a pest’s natural enemy to control it. For example, the soil bacteria bacillus thuringienisis produces a toxin that is deadly to certain insects but is apparently harmless to humans and other animals.

Some farmers use ladybugs, wasps or spiders to control aphids or white flies.

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