1. Key Area 3: Crop protection
Unit 3: Sustainability and Interdependence

2. Ecosystem
An ecosystem is made up of a community of living things and their habitats.
The community consists of several populations of plants, animals and microorganisms which interact with one another and their non-living environment.
A balanced biological unit is formed.
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3. Balanced Ecosystem
This balance exists between the producers and consumers in the ecosystem.
A wide variety of plant species will compete with each other and live with the pests and microorganisms in that area.
The communities tend to be composed of small mixed populations.
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4. Crop protection
When crops are growing, the variety of species present is greatly reduced.
Only the crop species is required to be grown.
This can take the form of a monoculture – a vast population of one species grown over a large area for economic efficiency.
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5. Crop protection
This monoculture can present ideal growing conditions for weeds, pests and disease causing microorganisms.
These conditions spread quickly through a crop of the same species.
(It is harder for this to occur through a mixed population of plants).
These can reduce the crop’s yield significantly and are therefore of concern to farmers.
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6. Weeds Weeds are plants that grow where they are not wanted.
Weeds reduce crop productivity due to
Competition.
Release chemical inhibitors
Contaminate grain crops
Act as hosts for pests and disease.
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7. Weeds Annual Perennial How they grow Properties Examples
Growth from seed and disperse seeds in one year
Lives for more than 2 years, will generally die back over winter and grow in spring
Rapid growth
Short life cycle
High seed output
Long term seed viability
Storage organs
Vegetative reproduction
Rhizomes
Chickweed, speedwell
Dandelion, bramble
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8. Weeds
Vegetative reproduction involves the use of bulbs, tubers, runners.
These are all formed by asexual reproduction.
All plants that develop from these are identical to the parent.
Rhizomes are horizontal stems that run underground and produce roots and stems.
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9. Pests Pests can fall into 3 categories: Nematode worms Molluscs
Insects
Numerous in soil
Attack roots and become parasites.
Example is potato cyst nematode
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10. Pests Molluscs Insects Snails and slugs
Very damaging to tough green plants e.g. cabbage.
Insects
Plant eating insects e.g. caterpillar, greenfly
different stages in life cycle may cause problems
Feed on leaves, stems, roots, storage organs
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11. Damage done? What damage do these pests do?
Photosynthesis will be reduced due to damage to leaves
Damage to plant vascular tissue prevents sugar getting to growing tissues
Vigour and yield of plant affected
Other pests can transmit viruses into plants thus acting as vectors of disease.
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12. Disease Plant disease can be caused by bacteria, fungi or viruses.
These pathogens can be air or soil borne or spread by insects.
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13. Damage done? What damage do these diseases do?
Poorer yield of crop harvested
Product may be blemished/infected, this means it may be less acceptable to buyers or marketable
Storage life of product may be reduced as it is less healthy
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14. Control of weeds, pests and disease Cultural means
Weeds, pests and disease can be controlled by traditional non-chemical methods.
These methods are preventative rather than curative and require long term planning.
These are not a quick fix to a problem.
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15. Control of weeds, pests and disease Cultural means
These include:
Ploughing – burial of weeds at depth at which they die.
Time of sowing – sowing seeds before weeds germinate
Removal of weeds – removing weeds early allows crop to grow sufficiently to tolerate weed competition
Removal of alternative hosts – weeds bordering fields may harbour insect pests
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16. Control of weeds, pests and disease Cultural means
These include:
Destruction of crop residue – may harbour disease which is removed and therefore prevented from infecting next crop
Cover crop – grown on fallow part of field which prevents weeds from growing and germinating fully
Crop rotation – growing different crop plants on same piece of ground prevents pests that can only attack certain types of plants.
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17. Control of weeds, pests and disease Chemical means
These include: Herbicides
Chemicals used to kill weeds
They can be:
Selective: these are absorbed more through the wider/larger surface area of the weeds leaves and stimulate the rate of growth/metabolism. The weed exhausts its food reserves and dies. These are not absorbed as much by the narrow leaves of cereal and grass crops.
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18. Control of weeds, pests and disease Chemical means
These include: Herbicides
Chemicals used to kill weeds
They can be:
Contact: these destroy all green plant tissue that they come into contact with. Usually biodegradable and short lived in effect. Perennial weeds with storage organs can re-emerge quickly.
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19. Control of weeds, pests and disease Chemical means
These include: Herbicides
Chemicals used to kill weeds
They can be:
Systemic: these travel through the whole plant and enter the plants internal systems with lethal effects. Can reach underground rooting systems and kill them so are more effective.
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20. Control of weeds, pests and disease Chemical means
These include: Pesticides
Chemicals used to kill pests
They can be:
Contact: kills pest when it comes into contact with it e.g. spray acting on aphid. Or can act as protective layer on plant and is effective when pest lands on it.
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21. Control of weeds, pests and disease Chemical means
These include: Pesticides
Chemicals used to kill pests
They can be:
Systemic: absorbed by the plant and ingested by insect when insect sucks up sugary sap.
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22. Control of weeds, pests and disease Chemical means
These include: Fungicides
Chemicals used to kill fungal parasites
They can be:
Contact: sprayed on plant and absorbed by fungal spores when they land on plant. Rain can wash these off. Repeated applications necessary.
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23. Control of weeds, pests and disease Chemical means
These include: Fungicides
Chemicals used to kill fungal parasites
They can be:
Systemic: absorbed by plant and transported throughout.
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24. Control of weeds, pests and disease Chemical means
What advantage is there in applying fungicides based on the weather forecast rather than treating diseased crop?
Crop yield has not been reduced due to already damaged crops and fungicide is not being used unnecessarily which can be costly and have environmental issues.
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25. Plant protection chemicals - problems
They may be persistent and last for a long time in the environment.
This means they may accumulate in food chains
e.g. DDT
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26. Plant protection chemicals - problems
Individual pests may be already naturally resistant to the chemical
This could be due to a feature such as an enzyme that breaks down the toxic effect of the chemical.
These individuals will be naturally selected for.
The pest may therefore become increasingly resistant to the chemical generation after generation.
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27. Definitions
Toxicity
How much of the chemical kills (different for different organisms).
Potential impact
Some organisms in the ecosystem may be killed and so knock on effects on the food web.
Persistence
How long a chemical remains/how long it takes to be broken down.
A high persistence chemical will remain for a long time, if you add it , it will build up.
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28. Definitions Bioaccumulation
The chemical taken in to an organism over time.
Potential impact
Chemicals can build up to toxic levels over time.
Biotransformation
Chemicals altered inside organisms.
A chemical that is not toxic could be altered to a damaging form.
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29. Definitions Biomagnification
Increase in concentration as you move up a food chain.
Potential impact
Animals further up the food chain may have toxic levels of the chemical
Resistance population
Population that is no longer killed by (sensitive to the chemical
Chemicals will become useless in the management of a particular pest/disease.
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30. Biological control
This occurs when a natural enemy of a pest is deliberately introduced where the pest is.
These enemies could be:
A predator of the pest e.g. ladybird predates on greenfly
A parasite of the pest e.g. Encarsia is a wasp that lays its eggs in whitefly and destroys it.
A pathogen e.g Bacillus thuringiensis is a bacteria which infects caterpillars and kills them
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31. Biological control Timing in biological control is crucial.
The prey must be able to be found and the crop must already be infested before the predator/parasite/pathogen is added.
The environmental conditions must allow the establishment of the predator/parasite/pathogen
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32. Integrated Pest Management
Integrated pest management combines chemical and biological controls.
It attempts to reduce the use of pesticides while also bringing down the levels of pests so they do not cause damage.
Control of the pest is the aim here rather than eradication.
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