TURFGRASS DISEASE IDENTIFICATION (P1)
Ectotrophic Root Infecting Fungi
Necrotic Ring Spot
Causal Agent: Ophiosphaerella korrae
Susceptible Turfgrass: Kentucky bluegrass, annual bluegrass, rough bluegrass, fine-leaf fescue
Symptoms: Necrotic ring spot first appears as small, light green spots and progresses to thinned, circular patches that are yellow to light-green in color and approximately 3 to 15 inches in diameter. The patches, which can expand up to 3 feet in diameter, even tually turn brown or straw-colored and die. The roots and rhizomes of the affected turfgrass turn brown to black. Grass plants can survive and recolonize the center of the patches, which leads to a ring-like appearance.
Conditions Favoring Disease: Necrotic ring spot initiates in moist soil, thrives in temperatures of up to 80°F and becomes more severe in higher temperatures and drought conditions. Seeded sites, as well as sodded sites in newly cleared woodlands, are susceptible to this disease. It is also found in areas with compacted soil and that are high in nitrogen during the spring and summer.
- Raise mower height.
- Reduce soil compaction through aerification and use of lightweight equipment.
- Use moderate to high amounts of phosphorous and potash.
- Maintain adequate nitrogen and a balanced fertility.
- Minimize the amount of shade.
- Lightly irrigate (approximately 1/10 inch) in the mid-afternoon on a daily basis to cool plants.
- Avoid drought stress.
- Top-dress and aerate turf as needed.
- Reduce thatch.
- Overseed with perennial ryegrass or more tolerant bluegrass cultivars.
- Apply systemic fungicides on a preventive basis.
Occasionally occurs in: CA, DE, KS, KY, MD, ME, MO, NC, NE, NH, NV, NY, VA, VT, WV.
Frequently occurs in: CO, CT, ID, IL, IN, MA, MN, NJ, OH, OR, PA, UT, WA, WI, WY.
Spring Dead Spot
Causal Agent: Ophiosphaerella korrae, Ophiosphaerella herpotricha, and Ophiosphaerella narmari
Susceptible Turfgrass: Bermudagrass and buffalograss
Symptoms: Infected bermudagrass shows disease symptoms as it emerges from winter dormancy. Spring dead spot appears as bleached, straw-colored, circular patches that measure up to several feet in diameter. The roots of affected plants turn dark brown to black.
Conditions Favoring Disease: Spring dead spot favors cool, wet weather in the spring and fall and daily temperatures of less than 60°F in November. This disease is typically found where thatch is more than 1/2-inch thick and in locations with poor drainage and low potash levels. Heavy applications of nitrogen in late summer often increase disease severity the following spring. Spring dead spot is more severe on bermudagrass that is over three years old and in locations with long dormancy and cold temperatures.
- Avoid late summer or fall applications of nitrogen fertilizers which may enhance disease severity.
- Use ammonium sources of nitrogen combined with potassium for fertilizer from spring through early August.
- Control weeds in affected turf to enhance recovery from spring dead spot.
- Apply moderate to high levels of phosphorous, potash, and minor elements.
- Improve drainage of turf.
- Reduce thatch.
- Convert from common varieties to hybrid bermudagrass with good winter hardiness.
- Use preventive fungicide applications in late September or October.
Occasionally occurs in: AL, AZ, CA, GA, IL, IN, KY, LA, MD, MO, MS, NM, NV, SC, SD, TX.
Frequently occurs in: AK, KS, NC, OK, TN, VA.