Two Pythium Diseases on Bentgrass Greens found in South-West Part of Japan

Abstract

This paper deals with two Pythium diseases causing foliar blights on golf greens of bentgrass (Agrostis palustris) in south-west area of Japan. One disease occurs under high temperature and extremely humid conditions, usually from middle to late of July and from late August to early September. Typical symptom is a round-shaped ring or patch, with characteristic reddish color and 5 to 50 cm in diameter. The causal agent was identified as Pythium aphanidermatum. The other one occurs in cool and hot seasons, from April to November. An irregular-shaped and pale brown patch, 1 to 5 m² in size. appears on greens where the turfgrasses have been exposed to unfavorable conditions. The causal agent was identified as Pythium vanterpolii.
Inoculation tests using bentgrass sods grown in pots revealed that the damage by P. aphanidermatum was weak at 15°C, moderate at 20°C and severe at 25 and 30°C, while that by P.vanterpoolii was visual even at 5°C and was severe at the temperature range of 15 and 30°C. Such difference in disease development is in good accordance with the characteristic behaviors of the occurrence of both diseases on golf greens. Mycelial growth on corn meal agar plates supports an idea that this difference is attributable in part to the characteristiics of temperature-dependent behaviors in the growth of each pathogen.