HET PLANTENRIJK
How do plant diseases spread?
Micro-organisms can cause diseases in plants as well as in humans and animals. Diseases are often infectious, which means that they can be passed on from plant to plant, usually by carriers such as insects, which may drink juices from a diseased plant and then inject them into a healthy one.
Plants are also attacked by parasites which can harm or even kill them. A parasite is an organism which lives on, or in, another organism. Parasites are never helpful, and are often harmful, to the host organism.
Chemical sprays and disinfectants enable farmers to kill parasites and to control plant diseases. These substances can be sprayed over wide areas from aeroplanes and helicopters. Many farmers depend on this form of crop protection to save their harvest of grain, fruit or vegetables. Without it, many people all over the world would die of hunger. However, these substances also cause widespread pollution because insecticides and fertilisers enter rivers and then the sea.