Influence of Spray Rate Volume and Surfactant Technology on Large Patch (Rhizoctonia solani) Control.

Large patch (Rhizoctonia solani) affects the stems and sheaths of Japanese lawngrass (Zoysia japonica) and is difficult to control using traditional fungicide sprays. Fungicides that are deposited lower in the plant canopy, where infection occurs, could improve large patch control. Field and greenhouse experiments were conducted in 2015 - 2016 to optimize fungicide efficacy using various spray rate volumes and surfactant additives. The first experiment evaluated azoxystrobin (0.61 kg ai ha^-1) applied at four different spray rate volumes (1500, 750, 375, and 95 L ha^-1). The second experiment evaluated azoxystrobin, flutolanil, and tebuconazole (0.61, 4.69, and 0.83 kg ai ha^-1, respectively) applied with or without an organosilicone surfactant (0.25% v/v).  Treatments were applied twice in the fall and once the following spring. Large patch control was assessed using digital image analysis to determine the percentage of diseased turf. These experiments were also conducted under greenhouse conditions. The influence of spray rate volume resulted in a greater impact on large patch control compared to the inclusion of surfactant additives in this research. On most rating dates, fungicides applied in higher spray rate volumes (≥ 750 L ha^-1) resulted in greater large patch control compared to lower spray rate volumes. Fungicides applied at higher spray rate volumes may result in greater fungicide deposition at the site of pathogen infection, leading to greater disease control. Future research on the combination of high spray rate volumes and surfactant additives are warranted.