There are many different diseases that turfgrasses can contract, but not all turfgrasses get the same diseases, except for one. That disease is called Leaf Spot. There are several different pathogens that cause leaf spot diseases that includes Helminthosporium, Drechslera and Bipolaris. They all belong to a large family of fungi that share the same descriptive name of leaf spots.
The Symptoms and Stages of Leaf Spot
For the most part, the infectious stage of leaf spot fungi occurs during the cool, wet and cloudy weather of spring or fall. Leaf spot can infect all parts of the grass plant; the initial symptoms show up on the grass blades as tan lesions with a reddish-brown border. The term “cigarette burn” is often used to describe the appearance of the lesions. If these cool, cloudy and wet conditions persist for a long time, leaf spot may cause grass blades to turn yellow as the lesions restrict movement of food and water up the grass blades.
The second stage of leaf spot is the more damaging stage. As the disease begins to infect more of the grass plant, the lawn will begin to slowly turn yellow and seem to be “melting” away. This is where the name of the second stage, the melting out stage, gets its name. The melting out stage occurs in early summer when it turns hotter and drier. Many homeowners think that the lawn is just going through some drought stress and will recover once it is watered. If the stem and crown tissues become infected, large sections of the lawn may be affected and recover is a more involved process that may require lawn renovation.
How to Prevent Leaf Spot From Damaging the Lawn
Although you cannot control the weather, you can make sure to follow good cultural practices to help ensure your lawn continues to grow well.
These cultural practices include:
• Increase mowing height to the highest range for the type of grass growing in your lawn.
• Water deeply, but infrequently, to provide 1 inch of water per week
• Do not water in the late afternoon through the evening hours
• Follow a balanced fertilization program that is best suited to the type of grass growing in your lawn
• Core aerate the lawn every year to promote stronger roots and keep thatch levels in check
There are disease control applications that can be applied and will help some if applied when the damage has already begun, but the best control from these types of applications happens when they are applied before the disease cycle begins in the early spring or fall. Keeping the lawn growing well is the best defense against leaf spot becoming a problem in the lawn.
There is another leaf spot disease, Gray Leaf Spot, that is active during warm, humid periods in the summer.This disease is very active on St. Augustine, perennial ryegrass and turf-type tall fescue. Instead of causing circular lesions, this disease starts out as tiny brown dots, which enlarge to irregularly shaped lesions. When humidity levels are high, the lesions taken on a gray tint, which gives the disease its name. The lesions have a distinct brown border between the healthy and diseased tissue.
If you feel your lawn may be having a problem with one of the leaf spot diseases, contact your local lawn care professional at Spring-Green to have them inspect your lawn!