Dead spot is a disease that primarily affects young stands of Agrostis and hybrid Cynodon spp. on golf putting greens and tees in the United States and Canada. It can also occur on overseeded Poa trivialis in Cynodon spp. greens. Dead spot is not known to affect turfs grown in native soils.
Causal agents
Ophiosphaerella agrostidis
Primary Hosts
Young stands (< 6 years old) of Agrostis and hybrid Cynodon spp. growing in sand-based putting greens.
Disease Cycle
Dead spot disease, caused by Ophiosphaerella agrostidis, primarily affects creeping bentgrass putting greens from May to October, with severe symptoms during hot, dry summers. It manifests as several hundred dead spots on putting greens, with milder symptoms on collars and tees. Common in sand mixes, it survives winter in crowns, stolons, and roots, as well as pseudothecia. Active at temperatures above 20°C (68°F), it attacks adjacent stolons or leaves, producing pseudothecia during summer. Ascospore release leads to secondary infections within days, forming reddish brown spots. When found in bermudagrass greens, the disease typically appears during spring greenup.
Epidemiology
Ophiosphaerella agrostidis, the causal agent of dead spot, thrives in temperatures ranging from 25 to 30°C (77 to 86°F). It reactivates in previously infected spots within 12 to 28 days after favorable temperatures return. The pathogen’s optimal temperature range is higher than that of cool-season grasses, giving it a competitive advantage over Agrostis spp. during the summer. Pseudothecia, which are responsible for producing ascospores, are rapidly generated as the days lengthen in early summer. Ascospores are dispersed by wind or water and can germinate and infect host tissues within hours. Ideal conditions can lead to a second generation of ascospores in as little as 12 days. Dead spot typically appears within 1 to 3 years of seeding or sprigging new greens and tees, as well as on older fumigated greens. In most cases, the disease naturally declines within 1 to 4 years after its initial occurrence, although it may persist for longer periods in alkaline soils.
Symptoms
Dead spot is a disease that primarily affects young stands of Agrostis and hybrid Cynodon spp. on golf putting greens and tees. In creeping bentgrass, it initially appears as small reddish brown spots that can enlarge up to 7.5 cm (3 in) in diameter. The center of the spot turns tan, while the outer edge remains reddish brown. In Cynodon spp., the patches are 5 to 7.5cm (2 to 3 in) in diameter, and infected leaves appear reddish brown or tan. Dead spots recover slowly, and stolon growth into the affected areas is often restricted.
Credit: John Kaminski/Penn State University
Signs
Mycelium is not observed in the field, but a pinkish, rose-quartz colored mycelium may be present on the leaves following incubation under high humidity for several days. Ectotrophic hyphae may be observed on the nodes of stolons in bentgrass and within roots in bermudagrass. Pseudothecia, commonly found in nature, can be found on necrotic tissues. Hundreds of asci can be observed within the fruiting bodies. Each asci contains 8 filiform (needle-shaped) ascospores that are twisted near the upper third of each ascus.
Credit: John Kaminski/Penn State University
Management
Although this disease is now rare, turfgrass managers growing in new putting greens should pay close attention to potential infections as the disease is difficult to manage. If disease outbreaks occur and control measures are not implemented, the disease symptoms can persist for nearly 8 to 9 months prior to recovery.
Cultural
Severe outbreaks of dead spot disease cannot be effectively controlled through cultural practices. However, when only a few dead spots are present, affected areas can be removed and discarded off site. The choice of nitrogen source is important, with ammonium sulfate being preferable over urea or nitrate nitrogen to minimize the recurrence of dead spot in subsequent years. Lime applications should be avoided as they can intensify the disease or result in future outbreaks.
Chemical
The use of an effective fungicide, combined with spoon-feeding nitrogen, can help halt disease development and promote recovery. During peak disease activity, the pathogen can infect and cause new infection structures within 12 days. Therefore, regular fungicide applications may be necessary every 10 days until full turf recovery is achieved. In the case of creeping bentgrass, it is crucial to control the disease and ensure complete recovery before winter. If not, disease symptoms will persist through the spring until early summer. In bermudagrass, rapid recovery occurs when temperatures become favorable for stolon and rhizome growth. Additionally, applying nitrogen during spring green-up can expedite the recovery process.
Specific fungicides that are optimal for controlling dead spot include boscalid (Emerald), fludioxonil (Medallion), and pyraclostrobin (Insignia). Although Insignia is an effective fungicide, it is important to note that other QoI fungicides do not provide suppression. The use of thiophanate-methyl (3336) is most effective for curative control of dead spot.