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Pest and Pest Control
Topic #6
What is a Pest?
 From the point of view of a farmer or forester, a pest
is any organism that causes plants to die or produce
less
 Obviously, some of these organisms wouldn’t see
themselves as pests – ex. Ants are part of the natural
system and just want to eat wood – not necessarily
bother foresters and trees!
Pest Problem
 Pests that cause most damage are:
 Insects – usually eat some part of the plant
 Fungi & Bacteria – can cause infections, destroying
part or all of the plant
 Weeds – are thieves and steal moisture, nutrients,
space or light from the plant
Dandelion – Super Pest
 Why are dandelions so successful?
 Powerful roots – long taproot that anchors it well
 Broad leaves – shade out other plants
 Super seeds – can produce flowers and seeds all
summer long – and hundreds of spreading seeds
 Adaptable – grow well in all kinds of soil
 Chemical weapons – release chemical agents to slow
down the growth of grass and other plants
Canola and its Pests
 Here are some of Canola’s worst pests:
 Canada Thistle – steals nutrients and water
 Wild Oats – same as above
 Blackleg Fungus – infecting seed pods and cutting the flow of
water through roots
 Sclerotina – infecting leaves and causing damage
 Fusarium Fingus – attacks stems
 Bertha Army Worm – eating everything in sight!
 Lygus Bugs – sucking the juice out of buds, flowers, seeds
Introduced Species
 Many of the worst weeds and insect pests are
organisms that were introduced from other
countries
 Many of the weeds that cause crop loss were
accidentally introduced from Europe: ex. Quack
grass, thistles, chickweed
 Dandelions were brought from Europe on purpose
as a salad vegetable, but the natural controls for
dandelions did not come with them!
Controlling Pests
 There have been many methods used to control
pests
 Large pests can be chased or scared away
 Smaller pests can be picked off plants by hand
 Farmers used to rotate crops each year to control
weeds and diseases
 Regular summer fallow also helped control weeds
and crop diseases but led to soil erosion
Chemical Controls
 When first introduced, chemical controls were
effective and relatively inexpensive
 Herbicides, insecticides and fungicides controlled
weeds, insects and fungus
 The chemicals were simple to use, gave impressive
results and WERE considered to be safe
 It took many decades for humans to figure out they
weren’t as great as first thought
Problems with Chemicals
 Pollutants such as chemicals in pesticides can
accumulate through the food chain – bioaccumulation
 Some chemicals wash off the plant and leave residues in
the soil and water – they can remain in the environment
and remain poisonous
 Chemicals can also harm organisms that are not the
target of the chemicals and can actually worsen the pest
problem
 With increased chemical use, some species have become
resistant so new and more dangerous chemicals must be
used
Organic Food
 Organic food is food that has been grown without
the use of chemical fertilizers and chemical
pesticides
 Organic food growers use manure and compost to
add nutrients to the soil
 They fight weeds and other pests using a
combination of methods such as tilling, crop
rotation, mulching, companion planting and
removing insects by hand or biological control