Pythium Blight of Turfgrasses

Ned Tisserat 
  Extension Specialist, Plant Pathology

Symptoms

Pythium blight, sometimes called cottony blight, is one of the most destructive turfgrass diseases. Susceptible turfrasses include perennial ryegrass, creeping bentgrass and tall fescue. Injury to Kentucky bluegrass , bermudagrass and zoysiagrass is rare in residential landscapes. Symptoms of Pythium blight are variable depending on the turfgrass species affected and the height at which the grass is cut. On bentgrass and perennial ryegrass mowed at fairway height, the first symptoms are small, irregularly-shaped, water soaked, greasy patches up to 4 inches in diameter. A cottony growth may be present in patches early in the morning. The patches may merge and form streaks since the fungal-like organism may be spread by mowing equipment or water.  Diseased plants eventually turn straw color and wither, resulting in crater-like depressions in the turf. Symptoms progress rapidly during favorable weather and large areas may be extensively damage within a matter of days.

Pythium blight is erroneously believed to be common on creeping bentgrass putting greens. In fact this disease rarely occurs on bentgrass mowed less than ¼ inch in height. It is not uncommon to find Pythium blight on the putting green fringe yet see no damage on the putting surface.

Pythium blight occasionally affects tall fescue during hot, humid weather. Softball-sized patches of water-soaked turfgrass form during hot wet conditions.  Diseased grass blades within the patch tend to stick to one another and have a mushy texture. Spots may coalesce and streaks may also form. Pythium blight will commonly develop along water drainage patterns in the turf. Affected plants eventually wilt and die to the crown. However, crowns and roots may not be killed and plants may recover after several weeks.

Pythium blight may also be a common cause of damping off and seed rot during turfgrass establishment.

Figure 1.  Pythium blight on perennial ryegrass.

Figure 2.  Pythium blight on tall fescue.

Conditions for Disease Development

Pythium blight is most active when air temperatures are high (day temperatures 86 to 95 degree F with minimum night temperatures of
(68 degree F). The disease usually occurs when soil is saturated with water following extended periods of rain. Long dew periods high relative humidity, and lush, dense turfgrass growth also favors disease development.

Figure 3.  Pythium blight on tall fescue.

Figure 4. Pythium blight on tall fescue.

Disease Management

Excessive nitrogen fertilization stimulates lush growth that is more susceptible to Pythium blight. Maintain a proper balance of nutrients and avoid fertilizing during periods of Pythium blight activity.

Preventive fungicide applications during the summer months may be necessary on perennial ryegrass or creeping bentgrass golf fairways, but are not normally needed for putting greens or residential lawns in Kansas.

Fungicides used for control of pythium diseases of turfgrasses.

azoxystrobin

Fair - use only at high rates and as preventive

10-14 days

Heritage

ethazole

good

7-10 days

Koban, Terrazole

mancozeb

good

7-14 days

Fore, Dithane, Formec, Mancozeb, Protect

mefenoxam

good-excellent

14 days

Subdue MAXX

propamocarb

good-excellent

7-21 days

Banol

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Web updated 9/01/06
Web comments to jpierz@ksu.edu