Establishment of Creeping Bentgrass in Annual Bluegrass Fairways Using Glyphosate and Interseeding

Creeping bentgrass (Agrostis stolonifera L.) is a highly desirable cool-season turfgrass that produces a quality golf playing surface. Golf courses that are established with creeping bentgrass are often invaded by annual bluegrass (Poa annua L.) and other turfgrass species over a relatively short period of time. Interseeding and non-selective herbicides, like glyphosate, have often been used to increase creeping bentgrass on golf course fairways. The objective of this research was to determine the most effective glyphosate rate and application timing necessary to quickly increase creeping bentgrass populations through interseeding into predominantly annual bluegrass fairways, while keeping the golf course open for play. This study was conducted from July to October 2010 at the University of Minnesota Les Bolstad Golf Course (St. Paul, MN) and Michigan State University Hancock Turfgrass Research Center (East Lansing, MI). Glyphosate was applied to plots at 14, 7, or 0 days before seeding (DBS) at rates of 0, 0.28, 0.42, 0.84, 1.68, or 5.62 kg ai/ha (0, 0.25, 0.37, 0.75, 1.5, or 5.0 lb ai/acre). ‘T-1’ creeping bentgrass was slit-seeded into the entire plot area in two directions at a total rate of 73.2 kg/ha. Higher glyphosate rates provided the greatest increase in bentgrass abundance at both locations. The greatest bentgrass population increase (54%) was observed in Michigan for the 5.62 kg ai/ha (5.0 lb ai/acre) treated plots at 8 weeks after seeding (WAS). The glyphosate applications at 7 and 0 DBS had the longest duration of acceptable turf quality and the greatest increase in creeping bentgrass. Our results suggest optimal bentgrass conversion during mid-summer stress periods when interseeded at a rate of 73 kg/ha in combination with glyphosate applied between 0 and 7 DBS at 1.68 kg ai/ha (1.5 lb ai/acre) or greater.