Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Lawn and Turf -- Microdochium Patch (Pink Snow Mold)
 
Hosts: The disease is worse on bentgrass and annual bluegrass. Fescues, bluegrass, and ryegrass (under high fertility) also can be infected but to a lesser degree.
Cause: A fungus, Microdochium nivale (formerly Fusarium nivale), that survives in diseases grass and dead plant debris. The disease occurs in spring and fall and is very common in winter in western Oregon and Washington and in northern Idaho. The most severe damage is in early spring just as snow starts to melt. Snow is not required for damage to occur. Leaf–to-leaf spread of the fungus is favored by alternate thawing and snow cover, repeated frosts, cold fogs, and light drizzling rain. Infection is more a problem on turf cut low and in shaded areas. High nitrogen fertility also favors disease development.
Symptoms: During cool, wet weather, reddish brown circular patches (1 to 2 inches in diameter) of turf appear. White or pinkish fungal growth may be at the advancing edge of the patch. Patches may enlarge and coalesce to form extensive affected areas. The center is generally tan and may contain uninjured grass. In areas with snow cover, the fungus may grow beneath the snow or, more commonly, as snow melts.

Reddish brown circular patches (1 to 2 inches in diameter) of turf appear.

Fusarium patch on a mixed grass home lawn. The largest patch is 14 inches across. The white hyphae of the causal fungus can be seen within the patches.

 
Cultural control:

  1. Do not overfertilize with nitrogen and avoid any late fall fertilization. Also avoid urea. Use a balanced fertilizer with moderate nitrogen.
  2. Ammonium sulfate is all right on bentgrass greens but not on annual bluegrass greens.
  3. Mow and remove clippings until growth ceases in fall.
  4. Promote good air and soil drainage.
Chemical control: Not recommended for home lawns because grass often recovers when the weather changes. On golf greens and other high-maintenance turf areas, scout regularly starting in September. Concentrate scouting in early spring just as snow starts to melt. Apply fungicides once symptoms are detected. Tolerant strains of many fungal pathogens can become troublesome if a single fungicide is used exclusively in a spray schedule. To reduce the possibility of fungicide tolerance, alternate sprays with fungicides having different modes of action.

  1. 26 GT Fungicide at 4 to 8 fl oz/1,000 sq ft. Use west of Cascades only. 24-hr reentry.
  2. Bayleton 50 T&O at 1 to 2 oz/1,000 sq ft. Landscape only, not for use on plants for sale. 12-hr reentry.
  3. Compass O 50 WDG at 0.25 oz/1,000 sq ft. Do not use organosilicate additives or more than two sequential applications. 12-hr reentry.
  4. Daconil Weather Stik at 5.5 fl oz/1,000 sq ft. 12-hr reentry.
  5. Defiant at 3 or 8 oz/1,000 sq. ft. in 2 to 5 gal water. Not for use in sod or seed production. 24-hr reentry.
  6. Disarm 480 SC at 8 to 16 fl oz/A. Do not use more than two (2) sequential applications. 12-hr reentry.
  7. Eagle 20 EW at 1.2 to 2.4 fl oz/1,000 sq ft. May produce a growth regulation effect on Kentucky bluegrass. 24-hr reentry.
  8. Heritage at 0.4 or 0.7 oz/1,000 sq ft depending on the number of applications. Alternate with other fungicides. 4-hr reentry.
  9. Insignia at 0.9 oz/1,000 sq ft. plus another fungicide with a different mode of action. Do not use more than 2 sequential applications or more than 5.5 oz/1,000 sq ft/year. Do not use with organosilicate adjuvants. 12-hr reentry.
  10. Instrata at 2.75 to 6 fl oz/1000 sq ft. A combination of group 3, 12 and M5 fungicides. Do not use on fine fescue. 24-hr reentry.
  11. Mancozeb 80% (Fore, Manzate, Penncozeb, and Protect DF) at 6 to 8 oz/1,000 sq ft. 24-hr reentry.
  12. Medallion at 0.5 oz/1,000 sq ft. Tank-mix with another fungicide. Using with oils or adjuvants may damage plant. 12-hr reentry.
  13. PCNB 75% (Terraclor, AmVac’s PCNB) at 8 oz/1,000 sq ft. Hi-Yield Turf and Ornamental Fungicide (10% PCNB) is also labeled at 5 to 10 lb/1,000 sq ft. 12-hr reentry.
  14. Propiconazole-based products. Apply once in late fall . 24-hr reentry.
    1. Banner MAXX at 2 to 4 fl oz/1,000 sq ft.
    2. ProPensity 1.3 ME at 2 to 4 oz/1,000 sq ft.
  15. Rubigan AS at 2 oz/1,000 sq ft under cool wet conditions west of the Cascade mountains or at 8 oz/1,000 sq ft under the continental conditions east of the Cascade mountains. Do not use more than 32 fl oz/1,000 sq ft/year. 12-hr reentry.
  16. Spotrete F at 12 fl oz/1,000 sq ft plus a latex based sticker. Repeat applications at each thaw with 3 fl oz/1,000 sq ft. 24-hr reentry.
  17. Thiophanate-methyl 50% products. 12-hr reentry.
    1. AllBan Flo at 2 to 3.5 fl oz/1000 sq ft. 12-hr reentry.
    2. Cleary's 3336 WP at 2 to 4 oz/1,000 sq ft.
    3. Trinity at 1 to 2 fl oz/1000 sq ft. 12-hr reentry.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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