This study was designed to measure turf quality and Poa annua population reductions on Bentgrass/Poa annua greens treated with paclobutrazole and dithiopyr concurrently. This study was conducted at Veenker Golf Course in Ames, IA on a sand-based practice green heavily infested with Poa annua. In the study area, the percentage cover of Poa annua was approximately 60%. Individual plot size was 5 x 5 ft and three replications were run.

Two fertilizer/herbicide treatments and an untreated control were included. One treatment consisted of Dimension 0.164% (10-3-10) applied concurrently with Turf Enhancer 0.13% (14-0-28) on May 1 and Turf Enhancer applied alone at 28 day intervals on June 8 and June 28, 2001. For the second treatment Dimension 0.164% (10-3-10) was combined with TGR 0.34% (15-0-29) on May 1, 2001 and TGR was applied alone eight weeks later on June 28, 2001. All granular materials were applied using a 'shaker dispenser' to ensure uniform coverage.

Turf quality was monitored from May 10 through September 5 (Table 1). Quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable and 1 = worst quality. Poa annua control was recorded from May 10 through September 5 (Table 2). Poa annua populations were determined by estimating the percentage area per plot covered by Poa annua. In addition, differences in the percentage of Poa annua seedhead production per plot were noted for May 15 and July 24 (Table 3).

Data were analyzed using the Statistical Analysis System (SAS Institute Inc., 1989-1996) and the Analysis of Variance (ANOVA) procedure. Treatment effects on Poa annua populations and visual quality were tested using Fisher's Least Significant Difference (LSD) means comparison test. In addition, Poa annua percentage cover means were compared using orthogonal contrasts in the General Linear Model (GLM) procedure (Table 4).

There was significant improvement in treated bentgrass quality on May 10, July 3, August 10, and August 15 as compared with the untreated control (Table 1). On other dates, numerical increases in quality ratings were noted but these were not statistically different. Treatment with TGR produced a definite color response in the bentgrass but not the Poa annua. The dark green bentgrass was in stark contrast to the lime green of the Poa annua and produced 'mottled or spotted' plots as compared to the untreated control and bentgrass treated with Turf Enhancer. Quality ratings on June 6 and June 15 reflect the distinct differences among the treatments but they are not statistically significant.

Populations of Poa annua were reduced in treated bentgrass from June 1 through July 3 as compared with the untreated control but the reductions were not statistically significant on all dates (Table 2). After July 3, Poa annua die-back resulted in greatly reduced populations in treated and untreated bentgrass and treatment effects are not significant.

Percentage Poa annua seedhead production data were taken when there was a large amount of seedhead formation on the practice green. On May 15, there were no statistical differences among the treated and untreated bentgrass (Table 3). On July 24, there were more seedheads in bentgrass treated with Dimension + Turf Enhancer than in bentgrass treated with Dimension + TGR or untreated.

The orthogonal contrasts show that on some collection dates Poa annua populations in treated bentgrass plots were significantly different when compared individually with the untreated bentgrass or the other treatment (Table 4).

Table 1. Visual quality¹ of creeping bentgrass on a sand based green treated for the 2001 Dimension + TGR/Turf Enhancer Safety Study.