SI3- crop protection

• Weeds compete with crop plants for light, water and nutrients, while other pests and diseases damage crop plants, all of which reduce productivity and crop yields
• Annual weeds only grow for one year. They drop seeds before they die- the seeds germinate the following year
• The properties of annual weeds are rapid growth, short life cycle, high seed output and long-term seed viability
• Perennial weeds do not die at the end of growing season. They lie dormant in the winter, but will regrow in the spring
• Competitive adaptations that allow perennial weeds to grow year after year include underground storage organs and vegetative reproduction
• Most of the pests of crop plants are invertebrate animals such as insects, nematode worms and molluscs
• Plant diseases can be caused by fungi, bacteria or viruses, which are often carried by invertebrates
• The control of weeds, pests and diseases of food crops is vital to ensure food security
• Cultural methods of controlling weeds, pests and disease include ploughing, weeding and crop rotation
• Pesticides include herbicides to kill weeds, fungicides to control fungal diseases, insecticides to kill insect pests, molluscicides to kill mollusc pests and nematicides to kill nematode pests
• There are advantages of using pesticides which are either selective or systemic
• Selective herbicides have a greater effect on certain plant species (broad leaved weeds)
• Selective pesticides remove only certain types of pests, leaving others unharmed
• systemic herbicides spread through the vascular system of plants including underground storage organs and roots thus preventing regrowth.
• systemic insecticides, molluscicides and nematicides spread through the vascular system of plants and kill the pests feeding on the plants.
• Applications of fungicides based on disease forecasts are more effective than treating diseased crops.
• problems with pesticides include:

  toxicity to non-target species
• problems with pesticides include:

  • toxicity to non-target species
  • persistence in the environment
  • bioaccumulation
  • biomagnification in food chains
  • producing resistant populations of pests
• Bioaccumulation is a build-up of chemical in an organism over time.
• Biomagnification is an increase in the concentration of a chemical moving up the trophic levels.
• In biological control, the control agent is a natural predator, parisite or pathogen of the pest.
• Examples of biological control include:

  • whitefly by parasitic Encasia
  • red spider mite by predatory mite phytoseiulus
  • butterfly caterpillars by bacterium bacillus thuringiensis
• the control organism may become an invasive species, parasites, prey on or be pathogen of other species.
• integrated pest management is a combination of chemical, biological, and cultural control.