Evaluation of selective fungicides by laboratory tests for the control of two Pythium diseases of bentgrass

Abstract

It is practically difficult to examine the chemical control of Pytium diseases on bentgrass golf greens, because the occurrence of the diseases is uncertain depending on climatic conditions. In this study, therefore, laboratory tests were conducted for the evaluation of fugicides selectively effective to Phycomycetes.
(1) Inhibition of mycelial growth and oospore formation was observed on corn meal agar plates containing six fungicides. The most effective chemicals on mycelial growth were metalaxyl and hydroxyisoxazole for Pythium aphanidermatum and were metalaxyl for P. vanterpoolii (ED₅₀≤1.0ppm) . Oospore formation of both fungi was inhibited to 50% by metaxyl and hydroxyisoxazole at concentrations of 0.2 to 1.3 ppm, respectively.
(2) Chemicals were sprayed onto sods of bentgrass (Agrostis palustris), and 5 days after a piece of mycelial mats was placed at the center of sods. Of six fungicides used, metalaxyl (80mg/m²) and fosetyl-Al (2.0g/m²) were highly effective on the disease development by P. aphanidermatum and P. vanterpoolii, respectively. Chloroneb and hydroxyisoxazole were also effective on both sods inoculated with P. aphanidermatum and P. vanterpoolii. Propamocarb seemed to be effective only to the disease by P. aphanidermatum. The tests with five chemicals mixed with non-selective fungicides confirmed high effectiveness of metalaxyl. Non-selective fungicides did not seem to enhance the activity of selective fungicides.