Disease management in warm-season turfgrasses requires providing a good growing environment, properly managing the turf, and accurately diagnosing any problems. Some key diseases include large patch, dollar spot, and fairy ring. Large patch is most active below 70°F and favors saturated soils with excessive nitrogen or thatch. Preventative fungicide applications in fall can provide good control. Spring dead spot damages roots and rhizomes over winter and recovery is slow. Aerifying, moderate nitrogen, and fall fungicide applications can help control it. Gray leaf spot favors warm temperatures and leaf wetness on stressed or slowly growing St. Augustinegrass.
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Disease Management Keys for Warm-Season Turfgrasses
1. Disease Management in Warm-
Season Turfgrasses
Lane Tredway
Associate Professor and Extension Specialist
Department of Plant Pathology
North Carolina State University
29. Conditions favoring large patch development
• infection occurs when soil temperatures are below 70°F
• saturated thatch/soil
• excessive nitrogen during periods of slow growth
• excessive thatch accumulation
• low mowing heights
31. Large patch is active when soil temperatures are below 70ºF
32. Controlling Large Patch with Fungicides
• preventative applications most effective
• initiate in fall when soil temperatures decline below 70°F
• one properly timed application will provide good control in
most landscape situations
• in severe cases, repeat applications on 4 to 6 week intervals
may be necessary
• curative applications help to reduce further spread, but
recovery will be slow
37. Spring dead spot symptoms appear in spring as the
bermudagrass resumes growth.
38. Spring Dead Spot Attacks All Below-Ground Tissues
Injury to roots, stolons, and rhizomes renders the bermudagrass
more prone to winter injury.
39. Conditions Favoring Spring Dead Spot Development
• any factor that restricts root growth
• soil compaction
• excessive thatch
• wet soils
• any factor that reduces winter hardiness
• excessive nitrogen in fall
• potassium deficiency
• wet soils
42. Speeding Spring Dead Spot Recovery
• avoid use of DNA herbicides in spring
- dithiopyr (Dimension)
- pendimethalin (Pendulum)
• aerify or spike affected areas every two weeks
• apply light and frequent irrigation
• apply 1 lb N per 1000 per month from May to Sept
45. Keys to Successful Control of SDS
• commit to implementing program for at least 3 years
• map affected areas in spring for treatment
• select an effective product
• apply preventatively in fall when soil temperatures
are between 60˚F and 80˚F
• water-in immediately with 1/8” to 1/4” of irrigation
47. Nitrogen Source Influences Spring Dead Spot
Dvelopment
Sulfur Coated Urea Calcium Nitrate Urea Ammonium Sulfate
Spring Dead Spot Index (diameter*incidence)
90 25
a
O. herpotricha a O. korrae
a
75 a
20 a
60
a 15
45 a a
a b a
a
10
30 ab
b ab
5
15 b a
b a a
c a b b
0 0
2007 2008 2009 2007 2008 2009
Nitrogen treatments applied monthy from May through August in 2006, 2007, and 2008
1 lb N per 1000 ft2 per application; 4 lbs N per 1000 ft2 per year
52. Gray leaf spot is most severe in St. Augustinegrass that is
growing slowly or is mowed infrequently.
53. Gray leaf spot rarely causes significant damage to well-managed
St. Augustinegrass.
54. Conditions Favoring Gray Leaf Spot
• 75ºF to 95ºF
• Extended periods of leaf wetness
• Most severe in newly established plantings
• High mowing heights and/or infrequent mowing
• Slowly growing turf
• Turf stressed by nutrient deficiency, drought, or traffic