IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Pythium Foliar Blight

Pathogen: Pythium spp., primarily P. graminicolaand P. aphanidermatum
Hosts: Perennial ryegrass, creeping bentgrass, Kentucky bluegrass and tall fescue

Symptoms and signs

On creeping bentgrass and perennial ryegrass mowed at fairway height, Pythium foliar blight first appears as scattered patches up to 4 inches in diameter (Figure 1). The patches often have a pinkish to red hue and a frogeye appearance, with greener grass in the center (Figures 2 and 3). The patches may merge and form streaks because the causal agent is readily spread by water movement in drainage patterns or by mowing equipment (Figure 4). Diseased plants eventually turn straw color and wither, resulting in crater like depressions in the turf (Figure 5).

Pythium foliar blight occasionally affects tall fescue and Kentucky bluegrass 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. Affected plants eventually wilt and die to the crown. However, crowns and roots may not be killed, and plants may recover after several weeks. When Pythium foliar blight is active, the margins of the patches are gray, and cottony mycelium may be evident, especially early in the morning (Figures 6 and 7). Lobate sporangia (reproductive structures) and hyphae with no cross walls are characteristics of Pythium spp. (Figure 8).
Pythium foliar 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 foliar blight on the putting green collar but see no damage on the putting surface.
Pythium spp. are also a common cause of damping off and seed rot during turfgrass establishment.

Conditions

Pythium foliar blight is most active when air temperatures are high (day temperatures 86 to 95°F and minimum nighttime temperatures of 68°F). Long dew periods, high relative humidity and lush, dense turfgrass growth favor disease development. The disease is severe in low-lying areas where soil is saturated with water following extended periods of rain or overwatering. Compacted and poorly drained sites are also prone to Pythium foliar blight. The disease will commonly develop along water drainage patterns. It also occurs on sites with poor air movement.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.