Plant Diseases

Plant diseases can reduce the productivity and beauty of our gardens and landscapes. Managing plant diseases does not begin with sprays.  Understanding plant disease begins with understanding the disease triangle, which demonstrates the connection between the plant, the disease-causing organism, and the environment.

Here’s how it works. You can avoid disease problems by planting a resistant species or variety of plant. Diseases usually do not spread from one species to another unless they are closely related. You can avoid disease problems by avoiding the environmental conditions that promote disease development. Most disease-causing fungi and bacteria flourish when foliage remains wet for extended periods of time and when temperatures are within a certain range. To put it simply, the more often it rains or you turn on the sprinklers, the more the potential for disease development increases. Finally, there is the third part of the triangle, the disease-causing organism itself. Sanitation means not bringing diseased plant material into the garden as well as removing diseased plant to reduce spread of the disease. Sprays to kill or hamper development of a fungus or bacteria are also a part of this third part of the triangle. When the other practices fail to prevent plant disease problems sprays may be necessary.

The resources included in this section will help you identify disease problems for various plants and choose the safest methods to manage them.