Diagnosis and spread of brown ring patch

Spring is a frantic, fever dream in the growth of Poa annua. While other turfgrasses wait for warmer temperatures, annual Poa annua stirs in the chill of the early thaw. Unlike creeping bentgrass, it does not seek the slow steady endurance of summer. It’s rapid, quiet and sudden eruption of seedheads is a defiant show of survival.

A drag on Poa annua is the plethora of diseases that can occur in spring. Many of the diseases can interact and maybe mask other diseases. The diagnosis of turfgrass diseases is rarely straightforward. It requires a comprehensive understanding of host-specific susceptibility, the subtle nuances between similar symptoms and the environmental conditions that favor pathogen development. Furthermore, cultural practices — such as mowing height and thatch management — significantly influence both the occurrence of disease and the clarity of symptom expression. These overlapping factors often make it difficult to determine if a single pathogen or a complex of organisms is responsible for turf decline.

The emergence of brown ring patch

Brown ring patch is a disease that gained considerable attention in the early to middle 2000s in the United States, predominantly affecting Poa annua. Caused by the fungal pathogen Waitea circinata, it was previously referred to as “Waitea patch” before “brown ring patch” became the accepted nomenclature.

Symptoms typically manifest as yellow to reddish-brown rings. These rings are often irregular or “scalloped” in appearance, ranging in diameter from just a few centimeters up to 30 centimeters. When moisture levels are high, mycelium may be visible on the foliage, crowns, stolons or within the thatch layer. Notably, the disease appears most severe on putting greens characterized by excessive organic matter (thatch) accumulation.

Differential diagnosis

Brown ring patch is frequently confused with yellow patch (Rhizoctonia cerealis) or fairy ring (caused by various basidiomycetes). Because all three present as ring-like symptoms on springtime golf course turf, accurate identification is critical:

Yellow patch, the disease often associated with these rings, can occur on creeping bentgrass (Agrostis stolonifera) and perennial ryegrass (Lolium perenne), but the symptoms are most widespread on Poa annua. Yellow patch occurs under cool (50-65 degrees Fahrenheit), wet and cloudy conditions commonly found in the spring in the temperate and oceanic climates.

Control

Brown ring patch presents control challenges due to the ability for the pathogen to infect over a wide temperature range. Symptoms can initially appear during spring under cooler temperatures of March, escalating in severity with increasing temperatures during the summer. In August, the heat-driven severity of Waitea circinata makes management difficult.

Effective suppression requires an integrated approach:

• Cultural controls: Prioritize the reduction of organic matter (thatch) accumulation, minimize leaf wetness duration and maintain balanced fertility levels.
• Chemical applications: When fungicides are used, high spray volumes are essential to ensure the product reaches the pathogen at the base of the plant and in the thatch.
• Timing: Preventive or early curative applications are significantly more effective than late-stage treatments.

With brown ring patch, I have found early diagnosis remains a vital component of a successful turfgrass disease control program.