Spring green-up – when warm season turfgrasses come out of dormancy and resume growth – is just around the corner. But sometimes, parts of the lawn don’t turn green. Cold injury from below freezing temperatures can cause root death in turfgrasses and prevent green up across affected areas of the lawn. When we see circles of dead grass, however, that is an indication of a disease problem.
Fungi cause most of the turfgrass diseases we encounter, and they often present as brown or straw-colored circles in an otherwise green lawn. Here are three common diseases that cause dead circles in lawns and what you can do to control them.
All photos credit to Alfredo Martinez, UGA Extension Turfgrass Specialist
Spring lawn diseases
Dollar Spot is the most common spring lawn disease. The fungal agent, Sclerotinia homoeocarpa, is always present incan affect all of the species of warm- and cool-seasons turfgrasses commonly used in Georgia.
In the lawn, dollar spot symptoms show up as sunken, brown or straw-colored circles that measure from a few to several inches in size. In heavily affected areas, the circles can merge to look like large, irregularly shaped patches. Weeds may begin growing inside the browned-out spots. If you inspect individual grass leaves, you’ll see small lesions with a reddish-brown border around yellowed or straw colored tissue.
Wet grass blades from rain or irrigation, combined with temperatures between 60 and 75 degrees Fahrenheit, encourage the dollar spot fungus to grow and spread. Dry soil conditions and poor fertility make the disease worse.
To manage dollar spot, irrigate early in the morning, while dew is still on the lawn, to minimize the number of hours grass blades are wet. Watering deeply and less frequently is better than watering for a few minutes several times a week. Remove thatch if it is deeper than 1 inch. Make light and frequent nitrogen applications, being careful not to over fertilize the turfgrass.
Brown Patch, affecting cool-season turfgrass species, and Large Patch, affecting warm-season turfgrasses, are caused by Rhizoctonia fungi. Brown patch symptoms usually show up in April and can remain active through October. High humidity and warm nighttime temperatures – 65 degrees Fahrenheit and above – along daytime temperatures over 80 degrees, prolonged leaf wetness, and excess nitrogen fertilization – are prime conditions for brown patch. Large patch is similar, with slightly cooler night temperatures (55 degrees F). In the lawn, these diseases cause grass dieback in large circles or patches, after which grass starts to regrow from the center of the circle.
Don’t apply nitrogen fertilizer when brown patch or large patch diseases are active. Remove thatch and raise the mowing height for the lawn. Irrigate in the early morning to reduce leaf wetness and minimize shade. Apply fungicides as recommended in the Georgia Pest Management Handbook (https://ipm.uga.edu/georgia-pest-management-handbook/) to manage the disease.
Spring Dead Spot (SDS) is a problem only in bermudagrass lawns. The fungi that cause SDS, Ophiosphaerella spp., actively feed on grass roots and rhizomes during the cool, moist conditions of fall and spring. This feeding weakens the grass and makes it more susceptible to cold and freeze injury. If the lawn has been affected by SDS, you’ll see large circles of dead grass that never green up when the lawn emerges from dormancy in April. Without active disease management, SDS can appear in the same spots year after year.
SDS infection usually starts in the fall, when soil temperature drops below 70 degrees Fahrenheit. The fungi continue feeding on roots until soil cools to below 50 degrees, then they wake up and begin eating again when the soil warms up in the spring. This is just about the time that bermudagrass resumes active growth.
Because the roots within SDS circles are dead, the only way to recover the grass is to direct stolons from the surrounding live grasses to grow into the dead spots. This is a slow process that requires several growing seasons.
Achieving control of SDS will also take a few growing seasons. Management actions include maintaining soil pH between 5.8 and 6.2, improving cold hardiness in bermudagrass through fall applications of potassium, and avoiding overuse of nitrogen fertilizer. Removing thatch and core aeration during active growth will also encourage deeper and more prolific root growth. Properly timed fall applications of fungicides can help reduce the presence of the causal fungi. This management practice may need to be repeated every fall until SDS symptoms stop showing up during spring green up.