Tall fescue performance in response to natural organic and synthetic granular fertilizers and <i>Rhizoctonia solani</i> inoculation

Abstract Repeated applications of natural organic based fertilizers can benefit soil health and potentially suppress some turfgrass diseases. One of the major summer diseases affecting many lawns is brown patch (caused by various Rhizoctonia and Rhizoctonia ‐like species). Information regarding the use of natural fertilizers to reduce brown patch in cool‐season lawns containing turf‐type tall fescue (TTTF) [ Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.] is limited. A 5‐year field study was conducted in West Lafayette, IN, to determine the influence of a wide range of commercially available natural organic based fertilizers on brown patch severity in a TTTF lawn. Seven natural organic granular fertilizers were compared to synthetic granular fertilizer, a granular fungicide control (FUNG), and a non‐fertilized control (UTC). Each fertilizer was applied at 24.5 kg N ha −1 in May, June, July, and late September/early October from 2020 to 2024. Visual turf quality, percent disease severity, and various soil properties were measured. During the five growing seasons, natural and synthetic fertilizer sources generally maintained higher visual quality compared to UTC. While the FUNG treatment was the most effective at reducing brown patch severity, select fertilizer sources reduced disease severity by as much as 70% compared to UTC. Brown patch severity for the fertilizer or fungicide treatments was generally not correlated with any soil property measured in this study. When selecting strategies to help reduce dependence on lawn fungicides, these data demonstrate that programmed seasonal applications of select fertilizer sources could be a component of a best management practices program to meet that goal.