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 multiyear field study was initiated to evaluate combinations of monthly applications of a biochar compost mixture and weekly or biweekly Bacillus subtilis QST713 applications for their ability to suppress foliar pathogens on a creeping bentgrass (Agrostis stolonifera L.) fairway and to measure their impact on strain QST713 establishment. Disease severity and turfgrass quality were measured every 14 days throughout the growing season. Populations of strain QST713 were quantified by quantitative PCR 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 strain QST713 applications reduced copper spot (Gloeocercospora sorghi D. C. Bain & Edgerton) severity compared with biweekly applications and the nontreated control in 2020, yet monthly biochar compost mixture with weekly strain QST713 applications completely suppressed copper spot in 2021. Populations of strain QST713 were highest in weekly treated plots, and monthly biochar compost mixture applications did not affect strain QST713 establishment. Although there was not an interaction between biochar compost mixture and strain QST713 applications, implementing both in a season-long program will benefit turfgrass health and reduce disease severity.

Investigating Chemical and Biological Control Applications for Pythium Root Rot Prevention and Impacts on Creeping Bentgrass Putting Green Rhizosphere Bacterial Communities.

Pythium root rot (PRR) is a disease that can rapidly devastate large swaths of golf course putting greens, with little recourse once symptoms appear. Golf courses routinely apply preventive fungicides for root diseases, which may alter the rhizosphere microbiome, leading to unintended effects on plant health. A multiyear field trial was initiated on a 'T-1' creeping bentgrass (Agrostis stolonifera L. cultivar T-1) putting green in College Park, Maryland to evaluate preventive PRR management for disease suppression and effects on rhizosphere bacterial communities. Fungicides commonly used to prevent PRR and a biological fungicide were repeatedly applied to experimental plots throughout the growing season. Rhizosphere samples were collected twice annually from each plot for evaluation of rhizosphere bacterial communities through amplicon sequencing and monitoring of biological control organism populations via quantitative PCR. Cyazofamid was the only treatment to suppress PRR in both years compared with the control. Fosetyl-Al on a 14-day interval and Bacillus subtilis QST713 also reduced PRR severity in 2019 compared with the nontreated control. Treatments did not significantly affect bacterial diversity or relative abundances of bacterial classes; however, seasonal environmental changes did. Repeated rhizosphere-targeted applications of B. subtilis QST713 appear to have established the bacterium into the rhizosphere, as populations increased between samples, even after applications stopped. These findings suggest that QST713 may reduce pathogen pressure when repeatedly applied and can reduce fungicide usage during periods of low PRR pressure.

Identification and Pathogenicity of Bacteria Associated with Etiolation and Decline of Creeping Bentgrass Golf Course Putting Greens.

Bacterial etiolation and decline has developed into a widespread issue with creeping bentgrass (CBG) (Agrostis stolonifera) putting green turf. The condition is characterized by an abnormal elongation of turfgrass stems and leaves that in rare cases progresses into a rapid and widespread necrosis and decline. Recent reports have cited bacteria, Acidovorax avenae and Xanthomonas translucens, as causal agents; however, few cases exist where either bacterium were isolated in conjunction with turf exhibiting bacterial disease symptoms. From 2010 to 2014, turfgrass from 62 locations submitted to the NC State Turf Diagnostic Clinic exhibiting bacterial etiolation and/or decline symptoms were sampled for the presence of bacterial pathogens. Isolated bacteria were identified using rRNA sequencing of the 16S subunit and internal transcribed spacer region (16S-23S or ITS). Results showed diverse bacteria isolated from symptomatic turf and A. avenae and X. translucens were only isolated in 26% of samples. Frequently isolated bacterial species were examined for pathogenicity to 4-week-old 'G2' CBG seedlings and 8-week-old 'A-1' CBG turfgrass stands in the greenhouse. While results confirmed pathogenicity of A. avenae and X. translucens, Pantoea ananatis was also shown to infect CBG turf; although pathogenicity varied among isolated strains. These results illustrate that multiple bacteria are associated with bacterial disease and shed new light on culturable bacteria living in CBG turfgrass putting greens. Future research to evaluate additional microorganisms (i.e., bacteria and fungi) could provide new information on host-microbe interactions and possibly develop ideas for management tactics to reduce turfgrass pests.

Plant Growth Regulator Effects on Bacterial Etiolation of Creeping Bentgrass Putting Green Turf Caused by Acidovorax avenae.

Bacterial etiolation, caused by Acidovorax avenae, is a widespread problem in creeping bentgrass putting green turf. The symptoms normally appear as abnormally elongated turfgrass stems and leaves. Observations at multiple field sites suggest the involvement of plant growth regulators (i.e., GA-biosynthesis inhibitors) commonly applied to turf, alluding to a phytohormone imbalance caused by the bacterium. A 2-year field study examined the effects of trinexapac-ethyl, flurprimidol, and paclobutrazol on bacterial etiolation severity caused by A. avenae. Trinexapac-ethyl applied at 0.05 kg a.i. ha-1 every 7 days and 0.10 kg ha-1 every 14 days increased etiolation compared with all other treatments in both years. Flurprimidol and paclobutrazol were not different from the control but high-rate applications caused phytotoxicity that lowered turf quality early in 2014. When the etiolated turfgrass was removed with mowing, turfgrass treated with trinexapac-ethyl exhibited the highest turfgrass quality on most rating dates. Results from this work illustrate that using plant growth regulator materials with different modes of action is a solution to managing creeping bentgrass growth while limiting the potential for bacterial etiolation outbreaks.

Anthracnose Disease on Annual Bluegrass as Affected by Foot Traffic and Sand Topdressing.

Sand topdressing is applied to maintain or enhance playability of the turf surface of putting greens. Anthracnose is a devastating disease of annual bluegrass (ABG; Poa annua) putting green turf, caused by Colletotrichum cereale. The disease is more severe on weakened turf and reputed to be exacerbated by management practices that wound turf. A 2-year field study was initiated in 2007 to evaluate the effects of foot traffic (0 versus 327 footsteps m-2, equivalent to 200 rounds day-1) and sand topdressing (0 and 0.3 liter m-2 every week) on anthracnose severity of ABG mowed at 3.2 mm. Surprisingly, foot traffic reduced anthracnose severity as much as 28%, regardless of sand topdressing, during both years. Although sand topdressing initially increased disease severity (up to 7%) in 2007, continued applications decreased severity by 9% later in August 2007 and again in 2008. The treatment combination of foot traffic 5 days week-1 and weekly sand topdressing resulted in the best turf quality by the end of both seasons. Results indicate that the practice of sand topdressing can be continued even under conditions of intense foot traffic and anthracnose disease development on ABG putting greens.