Diseases of cool season turfgrasses (
Rapid blight
Rapid blight is a new disease of cool season turf grass on golf courses in Arizona. Symptoms are invariably associated with fusiform or spindle-shaped structures observed in leaf cells (photo 1). These are the vegetative cells of Labyrinthula terrestris, an organism in a group referred to as the marine slime molds, but they are not true slime molds. One to several cells may be visible in cells of yellowing leaves (photo 2 & 3). Numerous spindle-shaped cells are visible under the light microscope when infected leaf tissue is macerated. (photo 4). Cells in culture form colonial networks and travel by means of gliding motility (photo 5). A species of Labyrinthula is known to cause disease of eelgrass, a marine plant, but none has ever been described as a pathogen of terrestrial plants. Initially, the causal agent of rapid blight was tentatively identified as a chytridiomycete fungus and became known as "chytrid disease", but this name is not applicable.
Early symptoms of disease include patches of turf that appear water soaked, slightly sunken and darker than healthy turf (photo 6). Affected turf yellows and dies (photo 7). Small patches several inches across may enlarge rapidly to over a foot in diameter, coalesce and result in larger areas of dead turf. Mowing and foot traffic seem to increase disease incidence rapidly. In a few cases, entire plantings of cool season turf seedlings have been lost.
Rapid blight has been reported in eleven states to date, and in most cases, including those in Arizona, disease has occurred on golf courses using irrigation water with salinity above 1.5 dS/m (about 1000 TDS), but is more problematic when salinity is above 3 dS/m. It also has been observed in several commercial lawns in Arizona. In Arizona, rapid blight occurs in fall and affects turf varieties used for overseeding bermuda: rough bluegrass (Poa trivialis), perennial rye (Lolium perenne), annual bluegrass (Poa annua) and colonial bent Agrostis tenuis). Bermuda appears to be unaffected, but L. terrestris has been found in Bermudagrasses: http://ag.arizona.edu/pubs/crops/az1421/az1421.4.pdf
Preventive treatments applied before symptoms appear, using mancozeb and/or trifloxystrobin (Compass) and pyraclostrobin (Insignia), have been effective in fungicide trials on golf courses with a known history of disease. Using salt tolerant varieties of turfgrasses and cultural methods for salinity remediation, such as routine applications of gypsum, help reduce disease pressure.
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For more information, please see the following web sites:
"Rapid Blight: A New Disease of Cool
Season Turfgrasses"
http://virtual.clemson.edu/groups/turfornamental/tmi/disman/rapid%20blight.htm
"Infection of Selected Turfgrasses by Labyrinthula terrestris"
http://cals.arizona.edu/pubs/crops/az1359/az13593d4.pdf
"Evaluation of Fungicides for Control
of Rapid Blight of Poa trivialis (2003)"
http://cals.arizona.edu/pubs/crops/az1359/az13593d1.pdf
"Evaluation of Fungicides for Control
of Rapid Blight of Poa trivialis in Fall 2005"
http://cals.arizona.edu/pubs/crops/az1421/az1421.3.pdf
"Investigations of the Host Range of Labyrinthula terrestris, a New Turfgrass
Pathogen"
http://
cals.arizona.edu/pubs/crops/az1359/az13593d3.pdf
"Response of Cool Season Turfs when
Overseeded on a Putting Green With a History of Rapid Blight Disease"
http://
cals.arizona.edu/pubs/crops/az1359/az13593d5.pdf
APS Feature article "Rapid Blight: A
New Plant Disease"
http://www.apsnet.org/online/feature/rapid/
December 26, 2006