Download Crop Protection

Higher Biology
Unit 3
3.3- Crop Protection
Weeds, pests and disease
• Weeds, pests and diseases are all issues
for farmers growing crop plants as they
reduce productivity
• This can be a huge issue where crops
are grown as monocultures as there is
less genetic variation and resistance to
disease and pests may be reduced
Monoculture
• A
monoculture
is the name
given to
single crop
species
grown over a
large area
Weeds
• A weed is a plant that grows somewhere
it is not wanted
• Weeds will compete for the crop plant
for resources such as water, lights, and
nutrients from the soil
• Weeds may also release chemical
inhibitors into the soil which affect
crop plant growth, and can act as hosts
for pests and disease
Annual Weeds
• Annual weeds grow quickly, have a short
life cycle and produce many seeds which
are viable for long periods of time
• Examples include:
Groundsel
Perennial weeds
• Perennial plants live for
many years, becoming
dormant in winter and
growing again in spring
•
• Some perennial weeds
have competitive
adaptations to ensure
survival such as storage
organs for food and
vegetative (asexual)
reproduction
Dandelions
Pests
• Pests of crop plants tend to be
invertebrates such as insects, nematode
worms and molluscs
Effects of pests
• Plant pests eat the leaves of the crop
plant which reduces their ability to
photosynthesise
• This reduces yield and vigour of the
crop
Plant Diseases
• Plant diseases are often carried by
invertebrates
• These diseases include bacteria, viruses
and fungi
Control of weeds, pests and
diseases
• Different methods can be used to
protect crops from harm
• These include cultural means, chemical
means and biological control
Cultural Means
• Ploughing a field can result in weeds
being buried deep enough into the soil
that they die and decompose
• Weeding can be used to remove weeds
and prevent competition
• This should be carried out early in the
life of the crop plant
• The perimeter of the field should also
be weeded to remove hosts for
pathogens
• Crop rotation means that pathogens are
unable to build up as they not able to
utilise the new crop
• The use of leguminous plants in crop
rotation allows for more nutrients to be
kept in the soil
Chemical control
• Chemicals can be applied to crops to
protect them from weeds and pests
• Herbicides are chemicals used to kill
weeds
• Insecticides are used to kill insect
pests
• Fungicides are used to kill fungal
parasites
Selective Herbicides
• Selective herbicides mimic hormones in
broad leafed plants causing their
metabolism to speed up. This results in
them using all of their resources more
quickly and they will die. Narrow leafed
plants are not affected.
Systemic Herbicides
• Systemic herbicides are absorbed by
the plant and enter its circulatory
system. This then has a lethal effect to
the roots and leaves of the plant.
Contact Herbicides
• Contact herbicides kill all green plant
tissue they come into contact with.
• The roots can survive and the plant can
grow back.
Contact Pesticides
• Contact pesticides work in 2 ways:
• They kill the invertebrates they come
into contact with directly
• Or
• They leave a residue on the plants which
will kill the pest at a later time
Systemic pesticides
• Systemic
pesticides are
absorbed by the
plant
• They will kill any
pests that try to
eat the plant
when they ingest
plant material
Contact Fungicides
• Contact fungicides are applied to plants
directly
• They will be absorbed by fungal spores
as they start to germinate causing them
to die
Systemic Fungicides
• Systemic fungicides are absorbed by
the crop plant and are not washed away
by rain
• They will only kill fungi affecting the
plant
Protective applications
• If there is a known crop fungus
outbreak fungicides can be applied as a
preventative measure
• This can be a more effective method
than trying attempting to treat already
infected plants
Biological Control
• Pest species can be managed using
biological control
• This is a method where a predator of
the pest species is introduced to
manage and reduce its numbers
• An example would be introducing
ladybirds to feed on aphids
Crop Protection Issues
• The use of chemicals can be useful to protect
crops but there are associated issues
• Chemicals may be non-specific and kill plants
other than those intended
• They may be toxic to animals
• They may persist in the environment and
accumulate in the food chain
• Their use can result in resistant populations
forming
• Biological control methods may upset the food
web and cause an ecosystem to collapse