Written by Colorado Green NOW

Unfortunately for the landscaping industry, gray leaf spot is a real problem. The disease can sprout up nearly wherever susceptible turfgrasses are grown. It can be found most often in the central transition zones of the U.S.

What is Gray Leaf Spot?

Many microorganisms in your lawn are beneficial, aiding in thatch decomposition. However, there are also a few harmful organisms that are parasitic forms of plant life called fungi. Fungi live in soil, thatch, and dead leaves within the lawn all year. These fungi feed on the grass by drawing nutrients from the plant and destroying the plant cells. Diseases spread, in the form of spores, throughout your lawn by wind, air, water, and traffic. The disease may re-appear from year to year if certain conditions are favorable. As a rule, areas that have been prone to disease problems in the past will at some time, if not yearly, have the same issues again. Gray leaf spot is a warm-season disease that affects primarily St. Augustine grass, Ryegrass, and Tall fescue turf. Gray leaf spot is a fungus that survives as mycelium and spores on infected plant material. Spores are produced during hot humid weather and are then spread by wind, watering, and mowing. Gray leaf spot starts as lesions on the leaves and stems during warm humid weather. The lesions will grow larger with time with a tan appearance in the middle surrounded by a brown to purplish margin. Severely affected areas will thin out as the grass blades wither and die, and turf will have a brownish appearance.

Damage

Gray Leaf Spot is the most severe during prolonged rainy, humid, hot periods usually occurring in midsummer. Temperatures that are optimum for Gray Leaf Spot are between 80 to 90 degrees Fahrenheit (26-32*C). High nitrogen levels will favor the disease and any other factor that may stress the lawn such as improper mowing, watering, and soil conditions.

Spot the Problem

Like many other turf pests, identification is key, as the issue can often be mistaken for other common problems like brown patch disease or Pythium blight.

Due to the large amounts of spores it can produce, you need to get aggressive with gray leaf spot once it is identified. Monitoring temperatures and how often watering happens is a great way to be proactive before damage starts. As it gets more severe and the plant starts to die, the dead plant has a hook at the end of the leaf. People tend to get grey leaf spot confused with Pythium blight.

Fungal Fighters

One of the best ways to prevent gray leaf spot is through proper turf care. Practices such as not seeding too early, avoiding excessive irrigation, removing wet grass clippings, and watering earlier in the day can all create an environment that is difficult for gray leaf spot to handle.

However, if the disease does root itself onto the host grass. A recommended way to deal with it is thiophanate-methyl. The biggest tip when you see gray leaf spot is to back off on the watering to slow the germination process.

Control

Slow-release nitrogen feeds the plant as it needs it through the root. This will help ensure healthy turf without leading to problems later. Watering properly is extremely important in this turf-damaging disease. Avoid watering at night during hot humid weather which extends the leaf wetness period and can lead to a greater chance of gray leaf spot disease. Allow air movement and light penetration, and prune back any trees and undergrowth. Always keep a sharp mower blade as well as allow the turf blade tips to heal quickly.