1Visual quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality.

The purpose of this study was to compare the efficacy of Scotts Turf Builder with Plus 2 weed control to that of competitive broadleaf herbicide products. The trial was conducted at the Iowa State University research station in an established area of 'common' Kentucky bluegrass. The soil was a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with 4.5% organic matter, 131 ppm K, 28 ppm P, and a pH of 7.6.

The experimental design was a randomized complete block. Individual plot size was 5 x 10 ft with three replications. Scotts Turf Builder with Plus 2 Weed Control, Sta-Green 200+ Weed & feed, Vigoro Weed & Feed, Ultra Vigoro Weed & Feed, Best Turf Supreme Weed & Feed, Bandini Superblade Weed & Feed, and Schultz Expert Gardener Premium Weed & Feed were furnished by Scotts for comparisons. All materials from other sources than Scotts were applied at label rate for bluegrass (Table 1). Trimec Classic 3.4 SL was included as a standard and applied at label rate. An untreated control also was added for a total of nine treatments. All materials were applied postemergently when dandelions were flowering but not in the puff-ball stage. Applications were made on June 22. All treatments except Trimec Classic 3.4 SL were made to wet foliage as per instructions. No irrigation was used for 24 hours following applications and there was no rain during this period. The plot was not mowed within 1 day before and after application.

On June 27, June 30, and July 7, dandelion and clover mortality data were recorded (Tables 1 and 2). Damage was assessed using a 0 to 100 scale with 100 = dead plants, 50 = 50% dead, 0 = no damaged plants. Dandelion and clover surviving populations were estimated from July 13 through August 17. The number of dandelions per plot was counted (Table 3) and the percentage area per plot covered by clover was estimated (Table 5). To account for the large number of small dandelions in some of the treated turf, percentage dandelion cover data were taken on August 17 (Table 3). Turf quality data were taken on each data collection date (Table 7). Quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable and 1 = worst quality.

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

On June 27, dandelions treated with either Trimec Classic 3.4 SL or Scotts Turf Builder exhibited substantial damage (Table 1). Dandelions treated with the other herbicide materials and those untreated had significantly less damage. By July 7, dandelions treated with the other materials had higher levels of damage than noted on previous days but the damage was still significantly less than on dandelions treated with either Trimec Classic 3.4 SL or Scotts Turf Builder.

Clover damage followed the same trend as dandelion damage. Trimec Classic 3.4 SL and Scotts Turf Builder caused significantly more damage than the other herbicides (Table 2). Damage caused by Scotts Turf Builder was statistically less than that caused by Trimec Classic 3.4 SL on June 27 and July 7 and mean damage also was less for Scotts Turf Builder.

Beginning with the data for July 13, all remaining dandelions were counted as survivors (Table 3). Trimec Classic 3.4 SL provided better dandelion control than all of the other herbicides except Scotts Turf Builder. Sta-Green 200+ and Vigoro Weed & Feed did not cause significant reductions in dandelion counts as compared with the untreated control for the entire duration. Overall mean values show that dandelion control was similar for Trimec Classic 3.4 SL and Scotts Turf Builder and better than provided by the other herbicides.

Percentage dandelion cover data from August 17 suggest that dandelion cover was significantly reduced by Trimec Classic 3.4 SL and Scotts Turf Builder (Tables 3 and 4). The levels for Trimec Classic 3.4 SL and Scotts Turf Builder were similar to those for Best Turf Supreme and Bandini Superblade.

Trimec Classic 3.4 SL killed all clover by July 13 (Table 5). Clover cover was significantly less in turf treated with Trimec Classic 3.4 SL or Scotts Turf Builder than in untreated turf on July 27. On this date there was more clover in turf treated with Sta-Green 200+, or Bandini Superblade or Schultz Expert Gardener than in untreated turf. By August 3, clover was declining in treated and untreated turf because of the hot and dry conditions and there were no statistical differences in clover cover for August but there were numerical differences. Clover control provided by Trimec Classic 3.4 SL, Scotts Turf Builder, Ultra Vigoro Weed & Feed, and Bandini Superblade Weed & Feed was „ 96% on August 17.

There were some statistical differences in turf quality between both treated and untreated turf and among herbicide treatments (Table 7). On June 30 all treated turf had better quality than the untreated controls. On July 7 and July 13, quality of treated turf was better for all treated turf than the untreated controls. Because of the hot and dry conditions, the quality of all turf was declining by July 20 and no additional differences in quality were detected for the duration of the study.

Table 1. Damage¹ observed on dandelions treated for the 2000 Scotts Postemergent Broadleaf Study.