Spring dead spot is a significant disease affecting Cynodon dactylon, Cynodon hybrids, Buchloë dactyloides, and Zoysia spp. in temperate climates. It is characterized by necrosis of roots, rhizomes, and stolons during winter dormancy due to the activity of multiple pathogen species. Unlike other turfgrass diseases, spring dead spot pathogens do not directly kill the turf but make it more susceptible to cold and freezing conditions. Therefore, management practices that enhance turf cold tolerance are crucial for effective control of spring dead spot.

Credit: PACE Turf

Causal agents

• Ophiosphaerella herpotricha
• Ophiosphaerella korrae
• Ophiosphaerella narmari

Primary Hosts

Cynodon dactylon and Cynodon hybrids. Spring dead spot is considered one of the primary diseases of bermudagrass.

Disease Cycle

Ophiosphaerella spp. survive in infected plant tissues like roots, rhizomes, and stolons. They spread through sod, sprigs, or debris, serving as sources of inoculum. The disease cycle involves initial colonization of roots, rhizomes, and stolons, causing lesions and widespread necrosis. Extensive necrosis leads to the development of necrotic areas. Pseudothecia, sexual fruiting bodies, may occasionally form. Symptoms primarily appear during cold conditions, with reduced freezing tolerance and lower supercooling capacity in infected plants. Winter dormancy makes infected bermudagrass vulnerable to freezing temperatures and desiccation, contributing to the persistence of spring dead spot symptoms.

Epidemiology

Temperature influences Ophiosphaerella spp. growth, with infection favored at soil temperatures below 21°C (70^oF). Inoculum sources like infected plant material spread the pathogens. The severity of spring dead spot can vary yearly, depending on favorable conditions for infection and symptom expression. Geographical distribution shows variations among different Ophiosphaerella species, such as O. korrae, O. herpotricha, and O. narmari. They may be more prevalent in certain regions or climates, impacting turfgrass species differently.

Symptoms

Spring dead spot symptoms are most prominent in spring when warm-season grasses resume growth after winter dormancy. Circular patches of turf appear dormant but are actually dead and eventually collapse, causing depressions. During fall, faint chlorotic patches may be visible, particularly after cool, wet periods. Affected patches may appear thin or slightly sunken compared to the surrounding healthy turf during winter dormancy. Recovery from spring dead spot is slow, often requiring the entire growing season, especially in severe cases.

Credit: John Kaminiski/Penn State University

Signs

Spring dead spot is characterized by circular patches of dormant turf that are actually completely dead, resulting in depressions in the turf. The roots, rhizomes, and stolons of infected plants exhibit severe rotting and appear black. Ophiosphaerella spp. produce darkly pigmented hyphae and mycelial mats on the infected tissues. Ascocarps (pseudothecia) of the causal fungi may also be found on dead tissues. Ascospores contained within pseudothecia vary in length and width and can be used to speciate the genera.

Credit: Peter Dernoeden/ University of Maryland

Management

Spring dead spot is the most prevalent and destructive disease affecting bermudagrass. This fungal disease can cause significant damage, resulting in unsightly patches and weakened turf. To effectively manage SDS, a comprehensive approach that combines cultural and chemical control strategies is essential. Cultural practices play a crucial role in reducing disease severity, while fungicides provide preventive control. By implementing a well-rounded management program that addresses both cultural and chemical aspects, turfgrass managers can effectively suppress SDS and maintain healthy, resilient bermudagrass.

Cultural

An integrated approach combining cultural practices and preventive fungicide applications is effective in managing spring dead spot. Selecting bermudagrass cultivars with improved winter hardiness and tolerance to the disease is important. Practices such as core aeration, alleviating compaction, and improving drainage promote root growth and reduce disease severity. Careful application of fertilizer and irrigation helps maximize root growth and enhance winter hardiness, while avoiding excessive nitrogen or potassium application in the fall, which can worsen the disease. Ophiosphaerella spp. respond differently to soil pH and nitrogen sources, and acidifying the soil with ammonium sulfate or elemental sulfur can effectively suppress O. herpotricha. However, consistent suppression of O. korrae has not been achieved with these practices. Long-term field trials have shown successful suppression of O. korrae with calcium nitrate, though the mechanism is not fully understood.

Additionally, cultural practices can aid in the recovery from spring dead spot symptoms during spring and summer. Cultivation techniques, such as disrupting the dead turf mat, promote the spread of healthy turf into affected areas. Light and frequent fertilization and irrigation are recommended, but excessive amounts should be avoided as they can worsen the disease in the long term. Preemergent herbicides that inhibit root development should not be used when spring dead spot symptoms are present, as they can impede recovery from the disease.

Chemical

Fungicidal control of spring dead spot can be inconsistent, and golf course superintendents should carefully evaluate if it is the best option for their situation. Research suggests that one spray often provides no disease control, and two to four sprays may be necessary for significant reductions in severity. Therefore, multiple applications or forgoing fungicides altogether might be preferable. Two applications approximately 28 days apart, when soil temperatures are between 60-80°F (16-27°C), are usually the minimum needed for some control. However, even with these applications, control can vary greatly. Immediate light irrigation after fungicide application may improve control, particularly with low spray volumes.

While disease control may not be complete, fungicides can sometimes improve turf survival and lead to rapid regrowth in affected areas. However, be cautious with propiconazole, as it was reported to increase susceptibility to frost and delay spring greenup. To minimize fungicide use, map affected areas and treat only those locations. GPS sprayers can be utilized to target fungicides specifically to infested areas, resulting in potential cost savings. Fungicide applications at spring greenup have shown no improvement in turfgrass recovery from the disease and may even cause phytotoxicity, especially with certain DMI fungicides applied during summertime.

Some fungicides that have been shown to be effective when applied in the autumn include:

• azoxystrobin
• isofetamid
• penthiopyrad
• tebuconazole
• combinations of effective active ingredients