1. Higher Biology
Unit 3
3.3- Crop Protection

2. 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

3. Monoculture
A monoculture is the name given to single crop species grown over a large area

4. 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

5. 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

6. 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

7. Pests
Pests of crop plants tend to be invertebrates such as insects, nematode worms and molluscs

8. 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

9. Plant Diseases Plant diseases are often carried by invertebrates
These diseases include bacteria, viruses and fungi

10. 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

11. Cultural Means
Ploughing a field can result in weeds being buried deep enough into the soil that they die and decompose

12. 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

13. 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

14. 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

15. 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.

16. 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.

17. Contact Herbicides
Contact herbicides kill all green plant tissue they come into contact with.
The roots can survive and the plant can grow back.

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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