| what do weeds do to crop plants | compete with them, reducing productivity |
| what do pests and diseases do to crop plants | damage them, which reduces productivity |
| what are the properties of annual weeds | rapid growth
short life cycle
high seed output
long term seed viability |
| what are the properties of perennial weeds with competitive adaptations | storage organs
vegetative reproduction |
| what are most of the pests of crop plants | invertebrate animals such as insects, nematode worms and molluscs |
| what are plant diseases caused by | fungi, bacteria or viruses, which are often carried by invertebrates |
| what is cultural control | involves practices which try to prevent any weeds, pests or diseases from getting established in the crop |
| give four cultural control methods | crop rotation
removal of crop residue
ploughing
weeding |
| give examples of pesticides | herbicides: kill weeds
fungicides: control fungal diseases
insecticides: kill insect pests
molluscicides: kill mollusc pests
nematicides: kill nematode pests |
| what type of plant are selective herbicides most effective on | Plants with broad leaved weeds |
| how do systemic herbicides work | they spread through the vascular system of the plant and prevent regrowth |
| how do systemic insecticides, molluscicides and nematicides work | they spread through the vascular system of plants and kill pests feeding on plants |
| what is more effective of crop protection than treating diseased crops | applications of fungicide based on disease forecasts |
| what are problems with pesticides | toxicity to non target species
persistence in the environment
bioaccumulation
biomagnification in food chains
producing resistant populations of pests |
| what is bio accumulation | build up of a chemical in an organism |
| what is bio magnification | an increase in the concentration of a chemical moving between trophic levels |
| can pests become resistant to pesticides | yes |
| what is the control agent in biological control | a natural predator, parasite or pathogen of the pest |
| what is integrated pest managment | a combination of chemical, biological and cultural control |
| what are the risks of biological control | the control organism may become an invasive species, parasitise, prey on or be a pathogen of other species |
