Lawn diseases occur when microorganisms attack a susceptible species of grass in the right environment. But before you can fight back, you have to determine what exactly is wreaking havoc on your lawn.

When attempting to identify a lawn disease, ask yourself these four questions:

1. Is my species of grass physically susceptible to this disease?
2. Are the environmental conditions right for the disease to activate?
3. Is this disease known to occur in my state or region?
4. Does this disease occur during this time of year?

You can rule out lawn fungus as a cause for damage to your grass by looking for these common scenarios where a lawn disease is not present but its symptoms are:

• Missing environmental conditions. This is the most common situation, where the pathogen is present and the turf is susceptible, but the weather conditions that cause the disease to develop aren’t present.
• Grass species is tolerant or resistant. If lawn fungus is present and the environmental conditions are right for disease development, the species of grass in your lawn could be either tolerant or resistant.
• Disease organism is not present. This requires a professional test to confirm. Contact a TruGreen® expert to help you get to the root of the problem.

Lawn disease only occurs if all three causes line up: grass susceptibility, a present pathogen and the right weather.

Grass Susceptibility

The type of turf grass in your yard can either be susceptible, tolerant or resistant to a lawn disease:

1. Susceptible: The turf hasn’t built up an immunity, so anytime the pathogen is present and the weather is favorable, that disease can reoccur.
2. Tolerant: The type of grass can be infected, but the disease will be less severe and recovery will be easier and faster.
3. Resistant: The species of grass can be attacked, but it resists infections and won’t show any symptoms or signs.

The Pathogen

Pathogens use your lawn as fuel for survival and reproduction. They can be one of several microorganisms:

1. Lawn fungus: The biggest cause of lawn disease, fungi can’t produce their own food, so they infect a host to eat. Fungi enter through leaves, stems, roots, natural openings, or wounds (sometimes caused through mowing). They’re spread by soil, rain or wind.
2. Viruses: Viruses are so tiny that they live within turf grass cells. They’re transported by mowers or insects carrying contaminated sap from diseased grass to healthy grass. 
3. Nematodes: These microscopic worms spread when soil or water moves, feeding on turf grass by using a piercing mouthpart to suck nutrients out of roots and stems.

Environmental Conditions

Lawn diseases each thrive in certain environmental conditions, including any one or more of the following:

1. Air Temperature: Lawn fungus diseases require certain temperatures to activate—mostly, the nighttime lows have to rise above a minimum temperature. 
2. Soil Moisture: This affects the humidity of your lawn’s surface and can either contribute to or prevent lawn disease development.
3. Relative Humidity: Free water or high humidity is required for infection to begin in most leaf diseases caused by lawn fungi.
4. Leaf Dew: How long accumulated dew sits on grass leaves is critical in foliar disease development. One key to lawn disease management is reducing dew drying times.

You can’t control the weather or the type of grass you have—but you can control your lawn’s environment through proper mowing and watering techniques to keep lawn disease at bay.

Cultural Control

While lawn fungus is a relatively minor problem, dead grass on your lawn is not. Every action you take has an impact on your lawn’s health, from fertilization to choosing a disease-tolerant or disease-resistant species of turf grass. For cool-season grasses, plant mixtures of different species. For warm-season grasses, mixing species isn’t possible, so picking the right turf grass for your region is critical.

Another good example of cultural control can be found in lawn diseases requiring excess water to develop. Reduce free water by decreasing the amount and frequency of watering, improving drainage and air movement and reducing thatch and shade so excess water and dew are both absorbed by the soil and evaporated to the air quicker.

Lawn Mowing Tips

Even when done properly, mowing stresses a lawn. When done improperly, it’s the most potentially damaging aspect of lawn maintenance. A lawn’s tolerance for disease is lowered—or even eliminated—by low-cutting or scalping your lawn. To help prevent lawn diseases like Brown Spot and Red Thread:

1. Mow at the correct height and frequency with sharp blades.
2. Don’t mow when your grass is wet or under drought stress
3. Always return grass clippings to the lawn (grass-cycle)

Water Management Tips

The two main types of lawn diseases are foliar and root. Foliar diseases attack grass leaves, and root diseases attack root systems—some diseases attack both. To reduce root diseases:

1. Don’t allow your turf grass to become stressed with too much moisture.
2. Water thoroughly and deeply—but not too frequently—to encourage deep rooting.
3. Use a turf syringe during the day to cool the root zone in severe cases.

Foliar diseases need extreme humidity and/or free water on the leaf to begin infections. Dew—and how long it stays on the leaf—is a critical factor. Dew forms based on temperature, air movement and humidity, so decrease shade to speed up your lawn’s morning drying time.

Yards with large trees on the eastern side of the property cause the western lawn to dry out more slowly, making them more susceptible to foliar lawn diseases. To reduce foliar diseases, water early in the morning, avoid overwatering and reduce shade by pruning tree limbs.