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Getting familiar with plant diseases

By: Barbara Ziesman Provincial Specialist, Plant Disease A.Ag, PhD

November 2016

Plant diseases can be very frustrating. Many of the diseases that producers deal with in Saskatchewan are not new. However, the management of these diseases can still be a major challenge. Over the course of the next year I will write a blog post once a month to highlight a pathogen (or related group of pathogens) of importance in Saskatchewan. In these blog posts I will cover the pathogen’s biology, the disease cycle, favourable conditions for disease development and disease management strategies. This month’s post focuses on some disease basics.

Plant diseases can be caused by both biotic (living) and abiotic (non-living) factors. When we refer to plant diseases, we often think about those that are caused by living organisms, such as fungi, bacteria or viruses. However, similar symptoms can also be caused by abiotic factors, such as adverse environmental conditions. It’s important that you’re able to determine what is causing the disease symptoms.

In Saskatchewan, though viruses and bacteria can be a concern in some situations, most plant diseases are caused by fungi and can be broken into two main groups: monocyclic and poly cyclic diseases. Monocyclic diseases are those diseases that only have a single disease cycle per season, whereas polycyclic diseases have many disease cycles per season. Polycyclic diseases, such as stripe rust, can increase exponentially over the growing season, making routine scouting very important.

A disease will only occur when the pathogen is present, the host plant is susceptible and the environmental conditions are conducive. These three factors together make up what is known as the plant disease triangle. The level of disease will increase when each point of the triangle becomes more favourable to disease development. This is a major reason why we often see disease levels fluctuate from year to year. Even if the inoculum levels, the part of the pathogen that can infect the host (such as the fungal spores), are constant and the same variety is grown there will be some differences in disease levels due to differences in the environmental conditions. As a result, having knowledge of the pathogen’s biology, host range and the environmental conditions that favour disease development can improve the management of the disease and assist producers in determining when to use management tools, such as fungicides, to reduce disease levels.

If you have a plant pathogen or disease that you would like to learn more about, please email me at Barbara.ziesman@gov.sk.ca and I will include it in the blog series. The first pathogen-specific blog will be released in December and will focus on Fusarium spp.

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