Topdressing Biochar Compost Mixtures and Biological Control Organism Applications Suppress Foliar Pathogens in Creeping Bentgrass Fairway Turf

Biochar, compost, and biological control agents can suppress pathogens on their own; however, their reliability and efficacy are not as acceptable as synthetic fungicides commonly used to suppress pathogens. A multi-year field study was initiated to evaluate combinations of monthly applications of a biochar compost mixture and weekly or biweekly Bacillus subtilis QST713 (QST713) applications for their ability to suppress foliar pathogens on a creeping bentgrass (Agrostis stolonifera L.) fairway and to measure their impact on QST713 establishment. Disease severity and turfgrass quality were measured every 14 d throughout the growing season. Populations of QST713 were quantified by qPCR analysis on DNA extracted from foliage samples collected throughout the trial. Biochar compost mixture applications increased turfgrass quality in both years of the study and reduced dollar spot (Clarireedia jacksonii Salgado-Salazar) severity in 2021. Weekly QST713 applications reduced copper spot (Gloeocercospora sorghi D.C. Bain & Edgerton) severity compared to biweekly applications and the non-treated control in 2020, yet monthly biochar compost mixture with weekly QST713 applications completely suppressed copper spot in 2021. Populations of QST713 were highest in weekly treated plots, and monthly biochar compost mixture applications did not affect QST713 establishment. While there was not an interaction between biochar compost mixture and QST713 applications, implementing both in a season long program will benefit turfgrass health and reduce disease severity.