Zionsville Times Sentinel

Now that summer weather is setting in, lawn diseases will begin to show up — overnight in some cases. Some folks think only poorly managed turf becomes infected. In fact, nearly every home lawn, golf course and athletic field will play host to a disease or two before the year is out. Understanding lawn diseases and properly managing turf will help to keep these pests under control.

The lawn disease triangle is an easy way to understand how lawns become infested with disease. The Ohio State University Master Gardener’s Web Site does a great job of explaining this philosophy.

Basically, for any lawn to become infected with a disease, the disease triangle must be completely fulfilled. The three points to the disease triangle are a susceptible plant, a pathogen (disease), and the opportune environmental conditions must exist. Even though different diseases affect turf at different times and under variable weather conditions, the triangle will always be fulfilled in the case of an outbreak.

Most lawns provide a susceptible host at some point in the season. When turf grass becomes stressed, it becomes more susceptible to a pathogen, given its more vulnerable condition. There are many factors that can stress turf. Some factors are: high moisture, low moisture, heavy traffic, mowing too low, mowing too high, hot weather, humid weather, and many more. With thousands of individual plants in your lawn, just a small percentage of susceptible plants can mean a sizable host.

The pathogens are existent nearly all of the time. Most lawn diseases are fungal diseases and are always present. In a “Red Thread Turf Grass Disease Factsheet”, the Cornell University Department of Turf Grass explains this particular disease will persist in the thatch layer of the turf. Many other fungal diseases that attack turf grass (dollar spot, snow mold, blight, rust, and brown patch to name a few) will also overwinter and “hide” in the soil, thatch layer and debris.

To make it simple, most diseases “hide” as spores or in other forms until the opportune conditions arrive and a susceptible host presents itself. The disease will then grow and persist as long as all points on the disease triangle are present.

The opportune environment varies for the type of disease. For example, Red Thread is running rampant in lawns right now. The heavy dew, temperatures and weather have been ideal for an outbreak. This disease will continue to thrive until the disease triangle is broken.

The conditions are fairly specific for each type of disease to spread. Some conditions that support the many different diseases include, heavy morning dew, high humidity, long grass, low fertility and high temperatures to name a few. When the right environmental conditions exist, and a pathogen and susceptible host are present, a disease outbreak can occur.

Controlling disease in turf can be tricky. Depending on the type of disease present, severity of the outbreak, and location of infection, the control means can be varied. For example, right now, most of our lawns are infected with red thread, a lawn fungal disease.

This disease is for the most part cosmetic, and poses no real long-term risk to the lawn. When the weather conditions change, the disease will go away. This disease can actually be somewhat controlled with a timely application of fertilizer. Although the timing and type of fertilizer are specific, there is no need for any other application. Other disease that cause significant damage and actually kill the turf should be treated.

Lawn fungicides are specific on what disease they control. Some products are curative, which eliminates the disease, while others are only preventative and have no impact on existing diseases. When dealing with these products, you will find that some are contact fungicides, others are systemic, and a few are penetrative. My recommendation when dealing with lawn diseases is to seek the help of a professional. Proper identification along with the proper control is the best way to beat these pathogens.

Although turf grass diseases can thrive in many different conditions, there are a few cultural practices that you can do to limit infection, and help to keep the disease triangle broken. Only water before sunrise, this ensures that the turf is wet for the shortest amount of time. A solid lawn management program that includes fertilization, weed control, proper mowing frequency and height will also go a long way for preventative measure. Having a professional monitor the lawn helps as most know when outbreaks can occur and can spot the diseases in its infancy.

Chris Arney is the owner of The Turf Boss, a Zionsville-based lawn and landscape service company. E-mail him at

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