Homeowner's Guide to Fungicides for Lawn and Landscape Disease Management1

Philip Harmon, Aaron Palmateer, and Rachel Ribbeck2

Homeowners are generally discouraged from using fungicide products to manage diseases of the lawn and landscape for the following reasons:

Fungicide products only help manage some plant disease, not all.
Selection of appropriate products is dependent on knowing what disease is being managed, which is difficult to do based on visual appearance alone.
Timing applications is tricky. In many cases, the window of time when best performance is likely is narrow, and recognizing that window requires close observation of the plant and environment. In addition, for some diseases, once symptoms have developed, there is no available curative treatment, and fungicide applications will help only with preventing spread to other areas.
Measuring, diluting, and applying products effectively and safely require attention to detail, some specialized skills, and equipment.
That being said, many fungicides are packaged for and marketed to homeowners; when used appropriately, these can help manage some lawn and landscape diseases.

What is a disease?
Plants die for many reasons, not all of which are diseases. Many environmental stresses cause disorders that mimic diseases. For example, drought stress can kill a plant. Disease occurs when a pathogen infects a plant and disrupts growth or kills that plant over time. The most common plant pathogens include fungi, bacteria, and viruses.

Disease Triangle
Environmental factors influence disease development in the landscape. When the environment favors the host plant, disease is unlikely to occur. When environmental factors favor growth of the pathogen and infection of the host, disease is more likely to occur. All three sides of the disease triangle (Fig. 1) must be present for disease to occur: a susceptible host, a pathogen that can cause disease, and an environment favorable for infection and disease development.

Copyright 2009