5.2.55
BIOLOGICAL CONTROL OF RHIZOCTONIA BLIGHT OF TURFGRASSES IN GOLF COURSES

BK CHUNG and JI CHUNG

Department of Agricultural Biology, College of Agriculture, Chungbuk National University, Cheongju 360-763, Korea

Background and objectives
Since turfgrasses grown on golf courses, parks and gardens may be harmed directly by various pesticides, and by mechanical and physical stresses such as uneven grass cut and walkers, they are under a weakened environment for infection by plant diseases. To maintain turfs, chemical application and agronomical practices are so heavily followed that contamination of the agoecosystem is a serious problem in recent years. In order to find out the effect of a newly formulated soil amendment, to select antagonists and to control brown patches of turfgrasses caused by Rhizoctonia solani AG1-1 and AG-2-2, a study was undertaken over the past 2 years.

Results and conclusions
Fourteen inorganic chemicals (1% w/w) in vitro individually suppressed R. solani. These chemicals, such as alum, suppressed 17-77% of mycelial growth compared with the control. The four chemicals Al2(SO4)3, alum, CaO and NH4NO3, were finally selected. Among orgnanic materials, composted pine bark was shown to have a greater suppressive effect than milled alfalfa leaves or pine leaves. After isolates AG1-1 and AG2-2 were inoculated onto turfs, water soaked lesions and blight symptoms developed on all seedlings. According to the inhibition zone method and mycelial growth of the fungi in culture filtrates of the antagonists, Gliocladium sp. (G1-1) and Pseudomonas sp. (P-13) were confirmed for their antagonistic ability. It is known that a CPB sod amendment mixed with antagonists (1% w/w) controlled not only brown and large patch of turfs, but also showed good growth of seedlings. In addition, its control effect was maintained for more than 30 days. In the case of the two antagonists, their control effect was similar to the CPB soil amendment with the antagonists combined with good growing conditions for the seedlings. It is therefore expected that continuous control may be possible in the field by repeated applications of the antagonists.

References
1. Huang JW, Kuhlman E, 1991. Phytopathology 81, 163-170.
2. Hoitink HAJ, Fahy PC, 1986. Annual Review of Phytopathology 24, 93-114.