Dollar spot, caused by at least five Clarireedia species (formerly Sclerotinia homoeocarpa F. T. Benn.), is one of the economically most important turfgrass diseases worldwide. The disease was detected for the first time in Scandinavia in 2013. There is no available information from Scandinavian variety trials on resistance to dollar spot in turfgrass species and cultivars (http://www.scanturf.org/). Our in vitro screening (in glass vials) of nine turfgrass species comprising a total of 20 cultivars showed that on average for ten Clarireedia isolates of different origin, the ranking for dollar spot resistance in turfgrass species commonly found on Scandinavian golf courses was as follows: perennial ryegrass = slender creeping red fescue > strong creeping red fescue > Kentucky bluegrass = velvet bentgrass > colonial bentgrass = Chewings fescue ≥ creeping bentgrass = annual bluegrass. Significant differences in aggressiveness among Clarireedia isolates of different origin were found in all turfgrass species except annual bluegrass (cv. Two Putt). The U.S. C. jacksonii isolate MB-01 and Canadian isolate SH44 were more aggressive than C. jacksonii isolates from Denmark and Sweden (14.10.DK, 14.15.SE, and 14.16.SE) in velvet bentgrass and creeping bentgrass. The Swedish isolate 14.112.SE was generally more aggressive than 14.12.NO despite the fact that they most likely belong to the same Clarireedia sp. The U.S. C. monteithiana isolate RB-19 had similar aggressiveness as the Scandinavian C. jacksonii isolates, but was less aggressive than two U.S. C. jacksonii isolates MB-01 and SH44. Thus, aggressiveness of Clarireedia isolates was more impacted by their geographic origin and less by species of the isolate and/or the host turfgrass species.
Seed mixtures with a nurse grass that germinates quickly at low soil temperatures can be an option for faster establishment of Agrostis stolonifera (AS) putting greens after winter damage. From 2015 to 2018 Poa trivialis (PT) ‘Dark Horse’ and Lolium perenne (LP) ‘Chardin’ were evaluated as nurse grasses in comparison with pure AS ‘Independence’ at two experimental sites in each of the two major climatic zones of the Nordic countries. Poa annua (PA) ‘Two‐Putt’ was also included as a nurse grass in the northern zone. As an overall trend, establishment was faster with AS+LP than with AS+PT and AS+PA, which in turn had faster establishment than pure AS. In the northern zone, AS+PT produced better turf quality than pure AS in the seeding year and year after and tended to be superior even on average for the entire trial period (mean value 6.0 vs. 5.8 for pure AS, 5.3 for AS+LP, and 4.6 for AS+PA; scale 1–9 where 9 is the highest quality). In the same zone, AS+PT also suffered less overall winter damage than the other combinations and was less infected with microdochium patch than pure AS. In the southern zone, PT and especially LP were far more persistent than in the northern zone and compromised turfgrass quality compared with pure AS. In conclusion, we recommend PT as a nurse grass for faster establishment of AS putting in the northern zone, but not in the southern zone where AS should rather be seeded in a pure stand.