3.3 - Crop Protection Flashcards
Monoculture
Vast population of a single species of crop grown over a large area for economic efficiency.
Crops
Crops are genetically identical and developed for productivity.
Risks to Productivity
Weeds: Compete for the same resources
Pests: Use crop as never-ending food source; causing damage
Disease causing microorganisams - Damages the crop and reduces overall yield.
Competition
Competition occurs for: light, soil nutrients, space, water.
Competition causes a decrease in productivity.
Weeds
Any plant that grows where it’s not wanted and causes competition with crop plants
Types of Weed
Annual (lives on year)
- Rapid growth
- Can establish self in vaccant land not colonised yet
- Large number of seeds
- Short life cycle
- Seeds can remain dormant but viable for long periods.
Pests
Herbivorous species which eat crop plants causing damage and a reduction in yield.
Types of Weeds
Perennial (more than one year)
- Competitive adaptations
- Already established in habitat
- Storage organs: Provides energy if the environment doesn’t favour photosynthesis
- Vegetative production e.g. runners or rhizomes
Pests
Intervebrates
Most pest species of crops are invertebrate animals. These include:
* Insects - different stages of an insects lifecycle damages different parts of a crop
* Nematode worms - parasites which damage crop plants by living in the roots
* Molluscs - possess rasping mouth parts that damage crop leaves
Disease
Pathogens that cause damage to crops and so reduce yield e.g. bacteria, fungi and viruses.
(Pathogen = foreign invading species)
Disease pt.2
Damage to leaves reduces the crop’s ability to photosynthesise and so cause a poorer growth which reduces the crop yield.
Crop diseases are usually carried by invertebrate pest species and reduces the crop’s productivity.
Control of Weeds, Pests and Diseases
Cultural Means
Time of sowing - Knowing when seeds planted are most likely to germinate and grow with least disturbance
Ploughing - Turns the top layer of soil to bury perennial weeds where they decompose
Removal of Alternative Hosts - By removing weeds (alternative hosts) in absence of crop plants, insects and disease can’t be established.
Cover crop - Planting crops that completely cover the ground during crop rotation stops any weeds from germinating.
Destroying crop residue - Removes any platform for pathogens to survive on
Crop rotation - Avoid pest species being established for more than one year
Selective Pesticides
Biodegradable and act like hormones to stimulate growth until all food reserves are used. This kills the weed before the crop.
Systemic Pesticides
Travels through the circulatory system (xylem and phloem) of the whole weed.
This is slower but kills all parts of the weed, including the root.
Crop absorbs the pesticides and transfers it through the vascular system of plants, killing the pests feeding on the plants.
Types of Pesticides
Insecticides - kills insects
Molluscicides - kills molluscs
Nematicides - kills nematodes
Systemic Fungicides
Fungicide is transported throughout the crop to prevent the growth of fungal spores on the crop.
Disease Forecast Fungicides
Through monitoring the temperature and humidity, fungicides can be applied to prevent the growth of fungi before they appear.
This is more effective than treating an already diseased crop.
Problems with Pesticides
Toxic to Animal Species
These chemicals could become toxic which would cause harmful effects to the animal.
Toxic to Animal Species
Biotransformation
Chemicals are altered when they are eaten by animals.
Problems with Pesticides
Persistence in the environment:
Bioaccumulation
Pesticides aren’t biodegradable so stay in the environment where they can accumulate as they work their way up a food chain to cause harmful effects.
Problems with Pesticides
Persistence in the environment:
Biomagnification
Pesticides increase in concentration as they move up a food chain meaning animals further up the food chain have more toxic levels of the pesticide.
Problems with Pesticides
Resistance to pesticides
The pesticide is useless in managing pests and disease-causing organisms due to selection pressures causing members of the population to no longer be affected.
Biological Control
Introduction of a natural predator, parasite, or pathogen of a pest species.
Risks of Biological Control
- Predator could spread to other ecosystems
- Predator could become pests themselves (cane toads in Australia)
- Need to wait until infestation has begun and predator
- Predator introduced may affect other species present (through predation or pathogen)
The use of pesticides on pest species is reduced by combining biological controls with pesticides. This reduces damage to the environment whilst controlling the pest to a manageable population size.
