Plants, like animals and humans, can also become diseased. In fact, there is a much wider number of plant diseases than there are human or animal diseases simply because there are more plant species involved in agriculture, horticulture and forestry than in medical or veterinary medicine.

The science of plant diseases is called plant pathology, or phytopathology. There are a wide variety of microorganisms such as fungi, bacteria, viruses and nematodes that cause these diseases. Diseases caused by these pathogens are often called biotic diseases. Also, environmental conditions, such as winter damage or drought stress, can cause disease in plants. Diseases caused by these factors are often called abiotic diseases.

Plant pathologists are responsible for studying plant diseases, and their studies include various aspects of plant diseases, such as the organisms and environmental conditions that cause disease in plants, the mechanisms by which these factors cause disease, the interactions between these causal agents and the plant, and methods for managing or controlling plant diseases.

The science of plant pathology is closely allied with other sciences such as botany, mycology, microbiology, genetics, chemistry, horticulture, agronomy, and soil science. Plant pathologists integrate and use information from many of these sciences to develop insights into disease development and disease control.

Why is Plant Pathology Important?

There are few if any crops grown in Canada or elsewhere that could be produced profitably without the efforts of plant pathologists. Farmers rely on plant pathologists for advice on disease-management strategies so they can produce a reliable, high quality crop. Canadian plant pathologists are in the forefront of efforts to develop new, environmentally-acceptable methods of disease control.

For relatively small investments in scientific manpower, Canadians have received new plant cultivars resistant to disease and new products to help fight plant diseases. For example, it has been estimated that relatively modest annual public expenditures in Canada to produce cultivars of wheat resistant to the stem rust disease have produced annual benefits (in increased yield) of over $216 million dollars.

Historical Effects of Plant Disease

Famine! Shortages of food severe enough to result in starvation are rare today but famine was a common enough occurrence in the past. For example, there are many biblical references to famine, and good evidence to suggest that many of these famines were the result of devastating epidemics of plant disease. Over two thousand years ago, the Greek philosopher Theophrastus studied (no doubt because of effects on supply and price of food) cereal and legume diseases.

One of the most infamous human disasters resulting from destruction of food supplies by plant pathogens is the Irish Potato Famine. The plant pathogen that caused the potato late blight disease, Phytophthora infestans, is still a threat to potato production today.

For a review of the history of plant pathology in Canada, see “Essays on the History of Plant Pathology and Mycology in Canada” by R. Estey. This book is available in many libraries – or can be purchased.

Plant Disease in the Modern World

Plant pathology has been astoundingly successful in providing farmers with methods for managing plant diseases. This success is one of the reasons why famine in today’s world is a relatively rare and isolated event. Nevertheless, plant disease continues to exert a toll on crop and food production.

Diseases cause several billions of dollars in lost production worldwide each year, reducing yields by over 500 million tonnes annually. These losses reduce profits to farmers and drive up prices of food purchased by consumers. In addition, current disease control measures are in some cases costly and inefficient.

Plant pathologists are working around the world to develop new, more efficient, and environmentally sustainable methods to manage plant diseases. For a current update on the world food situation, visit the home page of the Food and Agricultural Organization of the United Nations.

Teaching About Plant Pathology

Many members of CPS-SCP are actively involved with teaching about plant pathology to grade schools, colleges and universities. Teaching resources are developed by various members of our Society and are made available for teachers and members through the Educational Resources section of this website.

Downloadable Poster on Plant Pathology

This illustrated poster presents five contemporary examples of plant diseases, and briefly explains what plant diseases are and why they are important to Canadians. The poster can be directly downloaded as a “pdf” file and viewed directly on a computer screen, or printed out and used as a poster demonstration. To download, click on the following link: Plant Pathology in the Classroom. Plants get sick too!

You will need software such as Adobe® Acrobat® Reader® software to view this pdf file. This software can be downloaded free.

Learn More About Plant Diseases

If you would like to learn more about plant diseases and plant pathology, please browse around our CPS site and visit some of the weblinks to other related sites. Additional information can be obtained through your local library or by contacting members of CPS.