Fall is a great time to guard against spring and summer diseases on warm-season grasses.
Spring dead spot, or SDS, is one of the most common and important diseases on bermudagrass in Georgia. It is difficult to manage without an integrated approach. The disease is most common on intensively maintained turf like golf courses or lawns.
SDS causes dead patches
The characteristic dead patches appear in the spring when the grass is breaking dormancy, and the problem can persist well into summer. The fungus that causes the disease attacks the roots and stolons in the fall and winter. This makes the grass more vulnerable to winter freeze damage, which leads to the dead patches of grass.
Late September through October is the best time to apply preventative fungicide applications if SDS has been a problem this past season. But this won’t provide complete control. Most infections can be eventually eliminated over a period of years by combining fall fungicide applications with sound cultural practices.
But maintaining a disease free lawn in the coming years can only be accomplished by eliminating the stress that allowed the disease organisms to attack the lawn in the first place. Lawns are stressed by poor soil conditions combined with an imbalance of nutrients. Compaction, poor drainage and thatch thicker than one inch are linked to SDS outbreaks.
Follow these tips
Applying nitrogen late in the season or excess nitrogen, especially with a potassium deficiency, can encourage the development of disease. An integrated management program to improve the lawn’s health includes the following steps:
• When planting new lawns, use cold tolerant cultivars.
• Aerate and remove thatch regularly.
• Irrigate deeply and less frequently. (Once per week in the absence of adequate rain.)
• Mow at the recommended height. Low-mowing height stresses lawns.
• Monitor pH and nutrient levels on a regular basis with soil tests. Keep potassium and phosphorus in balance with nitrogen.
• Maintain a pH between 5.5 and 6.0 if disease has been a problem. The pH can be lowered by using ammonium sulfate as a nitrogen source.
• Apply moderate levels of potassium in September and October to increase cold hardiness. If a deficiency of potassium is indicated on a soil test, two applications of potassium sulfate or potassium chloride can be applied at a 3 to 4 week interval for a total of 1 lb. of K2O per 1,000 sq. ft. Excess potassium should be avoided as it can also encourage disease.
• Do not apply nitrogen after August. Nitrogen should be added in recommended amounts in late spring and early summer. Use moderate amounts of nitrogen during the summer so that excess nitrogen is not carried over into the fall.
• Apply fungicides in late September or October if SDS was a problem the previous spring.
Other warm-season grasses, such as zoysia, centipede and St. Augustine, will also benefit from these general recommendations to prevent diseases like take-all and Rhizoctonia large patch. Follow recommendations for fertilizer applications for the particular grass species. A pH of approximately 6.5 is generally optimum for warm-season grasses.
See these sites for more help
For more information on maintaining turfgrass in Georgia, see the website www.Georgiaturf.com. For fungicide recommendations, contact your local University of Georgia Cooperative Extension agent or consult the Georgia Pest Management Handbook for Homeowners at 0015 www.ent.uga.edu/pmh/ 415B .
(Elizabeth Little is the homeowner IPM specialist with the University of Georgia College of Agricultural and Environmental Sciences.)