This study was designed to screen arbuscular mychorrhizal material for effectiveness in improving the quality of creeping bentgrass and in reducing the growth of Poa annua. The experimental plot was on an established 'Penncross' creeping bentgrass sand-based practice green at Veenker Golf Course in Ames, IA with a relatively uniform Poa annua infestation in spring 2000. The experimental design was a randomized complete block with three replications. Individual plot size was 5 x 5 ft. The mychorrhizal material was applied at 0, 20, and 40 g/m² timed to correspond with core aerification of the green.

A Ryan GA30 aerifier was used with 5/8" cores spaced 2-1/2 x 3". Following removal of the cores, sand topdressing was added and smoothed across each 5 x 5' individual plot. The mychorrhizal material was added to the sand in the treated plots and raked into the cores. The whole plot was then overseeded with 'Penncross' bentgrass at 1 lb/1000 ft². The plot was watered under the normal watering schedule for the practice green.

The mychorrizal material was applied in the spring on May 16 when the Poa annua infestation was 70 to 80%. Percentage Poa annua cover data were taken throughout the season (Table 1) and because no differences among treatments were found, the material was reapplied on September 20, 2000. Turf quality of the bentgrass also was monitored and no differences were noted (Table 2). Additional percentage Poa annua cover data were collected fall 2000 until the bentgrass was dormant and no differences were found. The study was surveyed April and May 2001 and no differences in Poa annua cover and visual quality were found between treated and untreated bentgrass.

Table 1. Percentage Poa annua cover¹ in creeping bentgrass treated for the 2000 Arbuscular Mychorrhizal Poa annua Control Study.