This study was designed to evaluate the safety of quinclorac (Drive 0.75DF) on spring-seeded creeping bentgrass. The trial was conducted at the Iowa State University research station on a bare soil plot that was plowed, tilled, and prepared Spring 2000. The soil was a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with 4.1% organic matter, 84 ppm K, 16 ppm P, and a pH of 7.15. Three bentgrass cultivars were sown: L93 (Cultivar 1), Penneagle (Cultivar 2), and Penncross (Cultivar 3). Seeding rate was 1 lb/1000 ft².

The experimental design was a 2 x 7 factorial in a split plot design. Bentgrass cultivar was the main block and the six herbicide treatments were the subplot factors. Individual plot size was 5 x 5 ft with 3 ft barrier strips between rows. Assignment of bentgrass cultivar and treatment to plots within reps was made according to instructions followed at the other sites. Preparation of the site included tilling and raking. The soil was enriched with urea (46-0-0) at 1 lb N/1000 ft² and with triple super phosphorous at 1lb P/1000 ft².

Drive 0.75DF was applied 7 days prior to seeding (7 DBS), immediately following seeding (0 DBS), and 14 and 28 days after emergence (14 and 28 DAE). Emergence was defined as the time at which approximately 50% germination had occurred. Siduron was applied immediately following seeding at the highest label rate. No methylated soy oil (MSO) or other surfactant was used with Drive 75DF for this study. Sprayables were diluted in water and applied at an equivalent rate of 2 gal water/1000 ft². All treatments were watered in with 0.1 - 0.2 in water within 72 hours post application.

Seven days before seeding treatments were applied on 10 May 2000. It was cool (65º F) and mostly sunny with a light wind. The materials were applied between 12:00 and 12:30 pm using a carbon dioxide backpack sprayer equipped with TeeJet #8006 flat fan nozzles at 30-35 psi. Seeding was performed on 17 May 2000. Individual plots were hand-seeded and then raked. Immediately following, the O DBS treatments were applied. Seeding and treatment were finished by 2:30 pm. It was 75º F and mostly cloudy with SW wind gusts 15-20 mph. Seedling and application were performed between gusts so there was no drift of either seed or herbicides. A heavy rainfall occurred within 48 hours of seeding and some washout of seed into the barrier areas was observed.

Bentgrass emergence began on 25 May with grass observed in a few plots. By 29 May, bentgrass was present in all plots and this date was considered the seedling emergence date for the timing of additional herbicide treatments. The 14 DAE treatments were applied on 13 June. It rained 0.2 in approximately 3 hours post application. The 28 DAE treatments were applied on 27 June. It was 70º F and sunny with NW winds at 10 mph.

Percentage bentgrass and phytotoxicity data were taken weekly beginning 2 June. Bentgrass emergence was measured by estimating the percentage bentgrass cover within individual plots. Phytotoxicity and visual quality were assessed using a 9 to 1 scale with 9 = best quality, 6 = lowest acceptable, and 1 = worst turf quality.

By 8 June, broadleaf weeds were emerging. Purslane and prostrate pigweed were the predominate species. Beginning 15 June, percentage weed cover data also were taken and final weed cover data were taken 8 August. Weed populations were assessed by estimating the percentage weed cover per individual plot.

Data were analyzed using Statistical Analysis System (SAS Institute Inc., 1989-1996) and the Analysis of Variance (ANOVA) procedure. Treatment effects on bentgrass cover, weed cover, and visual quality were tested using Fisher's Least Significant Difference (LSD) test.

Slight differences in quality for all three cultivars were evident on 22 June (Table 1). Bentgrass treated with Drive 75DF on 13 June had a slightly faded appearance. This symptom was not observed on 15 June and was not apparent on 30 June.

None of the herbicide treatments significantly reduced the percentage cover of 'L93' bentgrass (Table 2). On 8 June, cover of 'Penneagle' bentgrass was less than the untreated control for all treatments except for the 28 DAE Drive 75DF application. Percentage cover of 'Penncross' treated with Drive 75DF at 7 DBS was higher than the untreated control on 7 July and 25 July. Treatment with Siduron at 0 DBS resulted in significantly more 'Penncross' cover than the untreated control on 7 July. Mean bentgrass cover data reflect no overall effect of the herbicide treatments on percentage bentgrass cover for the three cultivars.

There were significant decreases in percentage weed cover in treated versus untreated bentgrass on 2 August for all three cultivars (Table 3). Weed cover in 'Penneagle' was significantly reduced by Siduron 50WP on 14 July, 25 July, and 2 August as compared with the untreated controls. Siduron 50WP reduced percentage weed cover in 'Penncross' for the entire period except 15 June when compared with the untreated control.

Table 1. Visual quality¹ of creeping bentgrass treated for the 2000 Drive Bentgrass Seeding Study.

'L93'

'Penneagle'

'Penncross'