Silvery threadmoss has become a major weed problem on creeping bentgrass putting greens.  Carfentrazone is the only herbicide labeled for use against silvery threadmoss on putting greens and it requires repeated applications throughout the season for effective suppression of moss.  Several fungicides also have supplemental registrations for silvery threadmoss control.  After preliminary screening in the laboratory, selected treatments were field-tested to determine their potential silvery threadmoss control.  The objective of this study was to test the efficacy of several herbicide, fungicide, and herbicide + fungicide combinations for season long control of silvery threadmoss on golf course putting greens.

This study was initiated on three creeping bentgrass putting greens in Blacksburg VA in May18^th 2012 at the Turfgrass Research Center & Glade Road Research Facility, Virginia Tech.  The three creeping bentgrass cultivars were A4, L-93 and Tyee. Twenty six herbicide, fungicide or herbicide + fungicide combinations were applied in a randomized complete block design.  Any combination including a fungicide but not carfentrazone was applied every two weeks.  Any combination including carfentrazone was applied every three weeks.  All other products were applied once at study initiation.  See table 1 for treatments listed by application timing.  Visual cover, control, and injury ratings were taken monthly throughout the season as well as whole plot NDVI readings. 

At 8 weeks after initial treatment, three treatments performed equivalent to carfentrazone.  They included carfentrazone + chlorothalonil Zn + fosetyl-Al, 2,4-D amine, and Experimental #1.  In addition four treatments outperformed carfentrazone.  They included flumioxazin, sulfentrazone, Experimental #2, and oxyfluorfen.  Unfortunately those products which are more effective than carfentrazone can also be quite injurious to putting green turf.  Experimental #2 and sulfentrazone may have potential for turf safety and improved moss control; however, bentgrass variety testing needs to be performed to demonstrate safety to most varieties. 

Table 1.  Treatments listed in each box according to season long application timings.

Treatments	Application Timing
Chlorothalonil; chlorothalonil Zn; fosetyl –Al; mancozeb; mancozeb + CuOH	May 18th and every two weeks season long
carfentrazone; carfentrazone + chlorothalonil Zn; carfentrazone + chlorothalonil Zn, + fosetyl-Al; carfentrazone + fosetyl-Al	May 18th and every three weeks season long
2,4-D Amine; bensulide; methiozolin; pelargonic acid; MSMA; amicarbazone; fenoxaprop; flumioxazin; sulfentrazone; pyraflufen ethyl; Experimental #1; Experimental #2; oxadiazon; oxyfluorfen	May 18th at initiation only
2,4-D amine + carfentrazone; dicamba + carfentazone	Hormone applied May 18th; carfentrazone applied 10 days later