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

Key Area 3: Crop protection

Unit 3: Sustainability and Interdependence

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.

CfE Higher BiologySustainability

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Balanced Ecosystem


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• 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.

Crop protection


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• 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.

Crop protection


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• 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.

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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WeedsAnnual Perennial

How they grow

Properties

Examples


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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 growthShort life cycleHigh seed outputLong term seed viability

Storage organsVegetative reproductionRhizomes

Chickweed, speedwell Dandelion, bramble

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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Pests• Pests can fall into 3 categories:– Nematode worms–Molluscs– Insects

• Nematode worms – Numerous in soil– Attack roots and become parasites.– Example is potato cyst nematode


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Pests• Molluscs– 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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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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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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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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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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• 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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• 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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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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• 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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• 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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• 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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• 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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• 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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• These include: Fungicides– Chemicals used to kill fungal parasites

• They can be:– Systemic: absorbed by plant and

transported throughout.


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• 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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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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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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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.• Potential impact• A high persistence chemical will remain for a long

time, if you add it , it will build up.


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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.• Potential impact• A chemical that is not toxic could be altered

to a damaging form.


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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• Potential impact• Chemicals will become useless in the

management of a particular pest/disease.


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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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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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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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Documents

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