Control of Zoysia Grasses Diseases of Large Patch (Rhizoctonia solani), Curvularia Leaf Blight (Curvularla sp.) and Rhizoctonia Patch (Ceratobasidium spp.) with Acidif@ing the Soil Surface
Control of Zoysia Grasses Diseases of Large Patch (Rhizoctonia solani), Curvularia Leaf Blight (Curvularla sp.) and Rhizoctonia Patch (Ceratobasidium spp.) with Acidif@ing the Soil Surface S Umemoto, M Yasuda, S Kato, T Shingyoj'i and K Aoki Chiba Prefectural Experimental Agriculture Station, 808 daizenno-cho, Midorl-ku, Chiba-shi, Chiba 266, Japan Background and objectives Zoysia grasses (<1>Z. japonica and Z. matrella) are used in fairways, roughs and putting greens on Japanese golf courses. The most serious disease zoysia succumbs to in Japan is large patch but it is also susceptible to Curvularia leaf blight and Rhizoetonia patch. In 1990, the governor of Chiba Prefecture declared that new golf courses in the prefecture had to be maintained of without the use of agricultural chemicals. Studies aimed at establ'sh'ng procedures for the chemical-free maintenance of golf courses were initiated at the Chiba Prefectural Agricultural Experiment Station in 1990. Results and conclusions In the course of studying conducted to establish chemical-free disease control measures in zoysia grasses, it was found that adjusting soil pH to between 4.0 and 5.0 was very effective in suppressing the three target diseases. It was found that the soil need only be acidified to a depth of 1 to 2 cm to effectively control the diseases. Application of acidifying fertilizers such as ammonium sulfate, sulfur suspension concentrate and sulfa powder were all effective in lowering the surface pH and suppressing disease development. Sulfur powder application decreased pH only at the soil surface and maintained a low pH for several months. Two or three further applications a year are probably required to maintain the surface pH at a level discouraging disease development. The disease suppression mechanism induced by acidifying the soil surface was not clear, but it is now thought that the increase of free aluminum in the soil resulting from lowering of soil pH may have suppressed the diseases development or low soil pH may have changed in species or in the populations of soil-born microorganisms that are antagonistic to the pathogen, since incubation tests have showed that the growth rate of the causal fungi is not affected at a pH of 5.0. Control measures using a reduction of soil pH might be effective against all soil-borne zoysia grass diseases in view of the fact that they were found to be effective against three major diseases caused by distinctly mycological different causal fungi. Reference 1. Furuya H, Takahashi T, the late Ui T, 1996. Annals of Phytopatholog'cal Society of Japan 62, 69-74. 2. Umtmoto, S, Shingyoj'i T, Yasuda M, and Aoki K,1997. International Turfgrass Society Research Journal Volume 8, pp. 937-947.