Diseases are a major source of crop and plant damage that can be caused by a number of plant pathogenic (disease-causing) organisms. Fungi are the number one cause of crop loss worldwide. Viruses, nematodes, and bacteria also cause diseases in plants Symptoms resembling those caused by pathogens can be caused by abiotic (non-living) factors, such as nutrient deficiency and air pollution and also insects

Fungicides, herbicides and insecticides are all pesticides used in plant protection. A fungicide is a specific type of pesticide that controls fungal disease by specifically inhibiting or killing the fungus causing the disease. Not all diseases caused by fungi can be adequately controlled by fungicides. These include the vascular diseases Fusarium and Verticillium wilt. Diseases caused by other types of organisms, disorders caused by abiotic factors, and insect damage are not controlled by fungicides. Thus, it is essential to first determine the cause of symptoms before applying a fungicide.