Effects of Organic Amendments and Cultural Practices for Control of Large Patch (Rhizoctonia solani) on Zoysiagrass (Zoysia japonica) Fairway.

Organic amendments may suppress soil-borne pathogens by increasing soil microbial abundance and activity, which subsequently suppress fungal disease by antagonism, parasitism, and/or competition. However, little information is available on the use of organic amendments and their delivering methods to suppress large patch caused by Rhizoctonia solani on zoysiagrass (Zoysia japonica). The objective of this study was to evaluate the effect of different organic amendments delivered by topdressing or topdressing following aerification on soil microbial community composition and large patch on zoysiagrass. A two-year field experiment was established on a zoysiagrass fairway growing on native soil (silt loam) of a local golf course at Columbia, MO. The field plots were inoculated with R. solani in the previous fall, which resulted in disease development in more than 90% of the plots prior to the treatment application. Various organic amendments applied included an animal waste-based product (AW; Back to nature chicken manure), a sewage-based organic N fertilizer (ON; Milorganite), and a plant byproduct (PB; mustard seed meal), in addition to a synthetic N fertilizer (SN; UMAXX), a synthetic fungicide (SF; azoxystrobin), and an untreated control (UN). The materials were applied by topdressing with sand or topdressing following aerification twice a year (spring and fall) for two years. Except SF, all materials applied added the same amount of N approximately 150 kg ha^-1 per year. Over the two-year period, measured by area under disease progress curve (AUDPC), AW and SF reduced disease severity by 49% and 86% of those in UN, respectively. The ON, PB, and SN also showed reduction in AUDPC. However, the reductions were not significantly different from those in UN. Amendments applied resulted in a shift of soil gram positive to gram negative bacteria ratio based on phospholipid fatty acid (PLFA) analysis, with the similar trend as AUDPC. Cultural practices of topdressing and topdressing following aerification also influenced soil microbial community composition. Plots receiving topdressing following aerification showed significantly reduced stress indicators, including the ratios of fungi to bacteria, cyclopropyl 17 to its precursor, and saturated to monounsaturated fatty acid, compared to topdressing only. In conclusion, shifts of stress indicators induced by topdressing following aerification suggested suppression of fungi but stimulation of bacteria in soil.