Spring dead spot is a destructive disease of bermuda grass and bermuda grass hybrids. The disease occurs on stands of all ages but is most common three to four years after the turf has been established.
Three different root-rotting fungi are responsible for the disease and all three occur in Oklahoma. However, O. herpotricha appears to be the most common cause of the disease in our region.
The disease results in the formation of circular or arc-shaped patches of dead turf in early spring as bermuda grass breaks winter dormancy. The dead patches, which are slightly depressed and straw-colored, may range in size from several inches to several feet in diameter. The patches are normally randomly distributed throughout the lawn.
Roots and stolons of affected plants are dark brown to black and are severely rotted. During the summer bermuda grass slowly grows back into the bare areas, and by late summer there may be little or no evidence of the disease. Dead patches reappear the following spring in the same locations. After seven to 10 years, disease severity may begin to decrease to the point where the disease no longer appears in the lawn.
The disease tends to be more severe on high maintenance bermuda grass lawns. Excessive nitrogen fertilization during the summer months enhances symptom development the following spring.
Cultural methods may limit the severity of spring dead spot.
• Maintain a vigorous but not excessively lush turf.
• Lawns should be dethatched yearly when the bermuda grass is actively growing to promote good rooting.
• Core aeration may also reduce spring dead spot severity.
• Avoid excessive nitrogen fertilization. Application of excessive amounts of nitrogen (more than four to five pounds active nitrogen per 1,000 square feet per year) will increase disease severity.
• Avoid heavy applications of fast-release nitrogen fertilizers during the summer following a severe outbreak of the disease.
• Nitrogen applications should not be made after early August because this will increase turfgrass susceptibility to cold temperature injury.
• Avoid high pH (greater than 7). Application of ammonium sulfate helps reduce the pH.
• Maintaining adequate potassium has been shown to help improve winter hardiness and reduce disease damage.
Bermuda grass cultivars vary markedly in susceptibility to spring dead spot. None are immune to the disease, but several seeded and vegetatively propagated cultivars exhibit reduced patch sizes and faster summer recovery than susceptible varieties.
Vegetative cultivars with reduced susceptibility and which have performed well in our climate include Midiron, Midlawn and Patriot. For seeded varieties, Yukon and Riviera have reduced susceptibility and perform well in our climate.
Several fungicides, including fenarimol (Rubigan), propiconazole (Banner), myclobutanil (Eagle) and azoxystrobin (Heritage) are labeled for control of spring dead spot, usually calling for one or two applications in the fall. However, disease suppression with these fungicides has been erratic in trials. September applications of these fungicides have, in some years, reduced disease severity and enhanced recovery of the turf in the spring, but they did not completely control spot development.
Therefore, fungicide applications are not currently recommended for control of spring dead spot in our state.
If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office or visit our web site at http://countyext.okstate.edu/pottawatomie/.
