3.3 - Crop Protection

• Monoculture is the production of a single species of plant, often genetically identical, which can lead to ideal conditions for pests, weeds, and plant diseases to emerge
• Characteristics of annual weeds

  • Rapid growth
  • Short lifecycle
  • Produce large number of seeds
  • Long-term viability of seeds
• Characteristics of perennial weeds


  • Storage organs for food in all environmental conditions
  • Vegetative reproduction in addition to seeds
• Invertebrate pests


  • Molluscs - slugs and snails
  • Nematodes - microscopic worms, some of which can establish as parasites
  • Herbivorous insects like aphids
• Some invertebrate pests can carry plant diseases caused by fungi, bacteria, or viruses that lower crop yield and productivity
• Control of weeds, pests and disease

  Controlled by the farmer to ensure yield is not reduced
• Methods of control


  • Cultural control
  • Chemical control
• Cultural control


  Evolved from traditional methods of cultivation, preventative but requires long-term planning
• Cultural control means


  • Ploughing, Time of sowing, Critical time for removal of weeds, Removal of alternative hosts, Destruction of crop residue, Cover crop, Crop rotation
• Chemical control


  Used by farmers to improve crop yield as traditional methods alone are not enough
• Chemicals used in crop protection

  • Herbicides - to kill weeds
  • Fungicides - to kill fungal parasites
  • Molluscicides - to kill mollusc pests
  • Nematicides - to kill nematode pests
• Types of herbicide


  • Selective herbicide
  • Systemic herbicide
• Selective herbicide


  • Greater effect on certain plant species, mimic plant growth hormones, biodegradable, do not harm the soil
• Systemic herbicide


  • Enters the weeds vascular system, transported to all parts of the weed, lethal effect, kills underground organs and roots preventing regrowth
• Systemic insecticides, molluscicides, and nematicides

  Spread through the vascular system of the plants and kill pests feeding on the plants
• Some pesticides used in crop protection can be toxic to non-target species and persist in the environment, leading to bioaccumulation and biomagnification
• Chemical control can lead to selective pressure producing a resistant population of pests
• Use of disease forecasts

  Suggest applying a fungicide preventatively, more effective than treating a diseased crop
• Biological control


  Reduces pest population using natural parasite, predator, or pathogen of the pest
• Timing of introduction of biological control is important to avoid resistance, persistence, and introduction of harmful chemicals
• A heated glasshouse is an ideal location for biological control as it is enclosed and temperature can be altered to suit the specific control agent
• Biological control examples


  • Control of glasshouse whitefly with the parasite wasp Encarsia
  • Control of glasshouse red spider mite with Phytoseiulus
  • Control of butterfly caterpillars with the bacterium Bacillus thuringiensis
• Risks with using biological control include the control organism becoming an invasive species
• Biological control


  • Control of glasshouse whitefly with the parasite wasp Encarsia
  • Control of glasshouse red spider mite with Phytoseiulus
  • Control of butterfly caterpillars with the bacterium Bacillus thuringiensis
• Risks with using biological control include the control organism becoming an invasive species, or it becoming a parasite, predator or pathogen of another species
• Successful pest management includes a combination of cultural, chemical and biological control. This is known as Integrated Pest Management
• What is bioaccumulation?


  The build-up of a chemical in an organism
• What is biomagnification?


  An increase in the concentration of a chemical moving between trophic levels.
• What is a pest?


  Organism that reduces the yield of crops
• What does persistent mean?

  Unable to be broken down