TURFGRASS DISEASE IDENTIFICATION (P6)

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Rhizoctonia Diseases

Brown Patch, cool-season turf

Causal Agent: Brown Patch: Rhizoctonia solani

Susceptible Turfgrass: All species of cool-season turfgrass

Symptoms: The symptoms of brown patch can vary depending on the turfgrass cultivar, climatic and atmos pheric conditions, soil types and textures, and intensity of the turfgrass management. This disease typically appears as rings or patches of blighted turfgrass that measure 5 inches to more than 10 feet in diameter. The pathogen also causes leaf spots and “smoke rings”—thin, brown borders around the diseased patches that appear most frequently in the early morning. After the leaves die in the blighted area, new leaves can emerge from the surviving crowns. On widebladed species, leaf lesions develop with tan centers and dark brown to black margins.

Rhizoctonia Diseases

Conditions Favoring Disease: Brown patch is favored by high relative humidity as well as temperatures of over 85°F during the day and over 60°F at night. It occurs in areas that experience more than 10 hours a day of foliar wetness for several consecutive days. Brown patch infestation is more severe when the turf is cut to a height less than the optimum for that turfgrass species.

Management Tips:

  • Use low to moderate amounts of nitrogen, moderate amounts of phosphorous, and moderate to high amounts of potash.
  • Avoid fast-release nitrogen applications when the disease is active.
  • Increase the height of cut.
  • Increase the air circulation.
  • Minimize the amount of shade.
  • Irrigate turf early in the day.
  • Improve soil drainage.
  • Reduce thatch.
  • Remove dew from turf early in the day.
  • For best results, use contact or systemic fungicides to prevent brown patch.

Frequently occurs in: All states.

Labeled products:

Large Patch, warm-season turf

Causal Agent: Rhizoctonia solani

Susceptible Turfgrass: Zoysiagrass and other warm-season turfgrasses

Symptoms: Large patch (zoysia patch) appears as rings or patches of blighted turfgrass that measure 5 inches to 10 feet or more in diameter. Patches are brown to yellow in appearance, with a possible “orange firing” at the periphery of the patches. Small reddish-brown colored leaf spots occur on leaf sheaths, stems, and stolons. After the leaves die in the blighted area, new leaves can emerge from the surviving crowns. If the turfgrass is still green, the disease is most apparent down in the canopy, especially around the leaf sheaths as discolored/blackened lesions—when pulled lightly, these leaves detach very easily and are sometimes green above the damaged sheath.

Large Patch, warm-season turf

Conditions Favoring Disease: The symptoms of large patch can vary depending on the turfgrass cultivar, or climatic and atmospheric conditions, soil type and texture, and intensity of the turfgrass management. This disease is favored by high relative humidity, as well as temperatures of 50°F to 60°F at night in late fall or early spring. Infection is most likely when soil temperatures at a 2–4 inch depth decrease to 65°F. This is the period to apply preventive fungicides. Large patch infestation is more severe when the turf has high levels of thatch or is fertilized with nitrogen late in the season.

Management Tips:

  • Maintain balanced fertility.
  • Avoid nitrogen applications in the late fall through early spring when the pathogen is active.
  • Increase the air circulation.
  • Avoid overwatering.
  • Improve soil drainage.
  • Reduce thatch.
  • For best results, apply contact or systemic fungicides at no less than 2 gal/1,000 ft2 to prevent large patch.

Occasionally occurs in: DE, IN, KS, KY, MO, MD, VA, WV.

Frequently occurs in: AL, AR, AZ, CA, FL, GA, LA, MS, NC, NM, OK, SC, TN, TX.

Labeled products:

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