Conversion of Mixed Species Golf Course Fairways to Creeping Bentgrass Using Glyphosate.

Creeping bentgrass (Agrostis stolonifera L.) is a highly favored cool-season turfgrass, producing a quality playing surface. Golf courses that are seeded with creeping bentgrass often experience invasion by annual bluegrass (Poa annua L.) and other turfgrass species over a relatively short period of time. The objective of this research was to determine the most effective glyphosate rate and application timing necessary to convert existing mixed species fairways to a monostand of creeping bentgrass through the use of interseeding, while keeping the golf course fairway playable. This study was conducted during the summer of 2010 at Les Bolstad Golf Course (St. Paul, MN), Keller Golf Course (Maplewood, MN), and Michigan State University Turfgrass Research Facility (East Lansing, MI). The experimental design was a randomized complete block with four replicates. Glyphosate was applied to plots at 14, 7, or 0 days before seeding at rates of 0, 0.28, 0.42, 0.84, 1.68, or 5.62 kg ha^-1 a.i. 'T-1' creeping bentgrass was slit-seeded into the plot area in two directions with a Turfco TriWave^® slit-seeder at a total rate of 73.2 kg ha^-1. Results indicate that glyphosate applied at 1.68 and 5.61 kg ha^-1 a.i. provided the greatest reduction in mixed species populations, but had the lowest turfgrass quality ratings when compared to the lower rates. The glyphosate applications at 7 and 0 days before seeding had the longest duration of acceptable turf quality and the least amount of disturbance from slit-seeding.