Spring dead spot (SDS) is a major disease that affects bermudagrass in the United States and worldwide. Within the United States, the disease is most prevalent in the northern range of bermudagrass adaptation.

Oklahoma State University and Kansas State University researchers are focusing their efforts on gaining a better understanding of the way bermudagrass is infected, with the ultimate goal of developing improved control options.

Spring Dead Spot weakens the bermudagrass root system and predisposes it to winter injury.

Today we know the disease is caused by three root-rotting fungi: Ophiosphaerella herpotricha, Ophiosphaerella korrae, and Ophiosphaerella narmari (Tisserat et al., 1989). All three fungal species are found in the United States with O. herpotricha being the most abundant causal agent in the Midwest. O. korrae has been located throughout the United States and Australia. O. narmari has been isolated in California, Oklahoma and Kansas, and is a major pathogen in New Zealand and Australia (Wetzel et al., 1999).

The fungus usually takes from two to three years to become fully established. Symptoms of the disease include circular bleached and depressed thatch areas from 6 inches to 3 feet in diameter.

Once established, the below-ground roots and rhizomes are typically covered with dark brown to black fungal hyphae. Like many root-rotting fungi, this fungus is most active in the early fall and spring when temperatures and moisture favor fungal growth and when bermudagrass growth slows down.

In the fall, infection weakens the bermudagrass root system and predisposes it to winter injury. For this reason, the disease is more common in Northern colder climatic areas and during years of severe winter.

Quick Tip

Researchers have shown there is a close association between resistance to SDS and resistance to cold temperatures (Baird et al, 1998). In other words, bermudagrass varieties that resist the cold also resist SDS infection. Since freezing temperatures tend to increase damage, it stands to reason that cold-resistant varieties would show less damage than nonresistant varieties and would be less susceptible to attack by opportunistic fungi. Nus and Shashikumar (1993) showed that infection with O. herpotricha and O. korrae reduced the ability of a single bermudagrass line to adapt to cold temperatures, and that this lack was possibly related to changes in cell membrane properties.

With the coming of spring and warmer temperatures, bermudagrass breaks dormancy and spring growth continues. In diseased areas, damaged tissue often fails to regrow, leaving the characteristic circular patches containing dead and dying tissues. However, regrowth can occur from the margins of the infection zone and from surviving plants within the patch that results in a recolonization of the dead areas. Often recolonization by aggressive varieties may cause the summer patches to completely disappear. This seasonal cycle of infection and recolonization results in a variation in patch size from year to year. After five to six years, the symptoms usually subside and can even disappear for unknown reasons.

Damage reduction What can be done to reduce the damage caused by SDS? Unsightly patches of infected bermudagrass often require expensive remedies. The severity of disease symptoms increases with a number of environmental conditions and cultural practices.

Generally speaking, factors that delay fall dormancy or reduce winter hardiness tend to promote the disease. Excessive fall fertilization and an accumulation of thatch will also increase SDS infection.

Bermudagrass growing on soils that are poorly drained or have been compacted also show greater symptoms. Ned Tisserat, Kansas State University plant pathologist, recommends dethatching and core aerification to reduce damage cause by SDS (Tisserat, 2001).

What about fungicides? Unfortunately, disease control through chemical fungicides has been erratic. Control varies from year-to-year and usually requires more than one application.

Quick Tip

One of the best approaches for reducing SDS is the use of resistant bermudagrass varieties. The programs of Charles Taliaferro and Dennis Martin have been active in producing and evaluating SDS response in elite breeding lines and commercial varieties, respectively. Resistant varieties such as Guymon, Midlawn, Midfield, Midiron, Yukon, Mirage and Sundevil typically show less damage from SDS.

Yukon is a recently released seeded variety with substantial resistance to SDS. However, none of these varieties are immune to the disease, and some do not offer the quality demanded by golfers.

Susceptible varieties include Arizona Common, Cheyenne, Jackpot, NuMex Sahara, Oasis, Poco Verde, Primavera, Princess, Sonesta, Shanghai, Tifton 10, Tifway, Tifgreen, Tropica, Vamont and Sunturf.

Biocontrol of SDS may be a possibility in the future. Biocontrol agents usually consist of microorganisms that when applied kill or inhibit the growth of specific disease-causing organisms. Several biocontrol agents have been successful in controlling specific plant diseases. Recently, a bacterium was found by the laboratory of Michael Anderson that dramatically suppressed the growth of O. herpotricha on nutrient agar.