This study was designed to compare the efficacy of experimental broadleaf weed control formulations with selected commercial standards. 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. Two experimental formulations, NB20332 and NB30196, were screened at 4.0 and 5.0 pts/A. Another formulation, NB30401 was tested at 3.5 and 4.0 pts/A. A fourth material, NB30404, was tested at 4.125 pts/A. Trimec Classic at 3.5 pts/A and Millenium Ultra at 2.5 pts/A were used as commercial standards. An untreated control was included for a total of ten treatments (Table 1).

Sprayables were diluted in water and applied at an equivalent rate of 40 GPA total spray volume using a carbon dioxide backpack sprayer equipped with TeeJet #8006 flat fan nozzles at 30-35 psi. The treatments were applied on June 22 when the broadleaf weeds in the experimental plot were 1-4 inches high. It was 75 degrees and sunny with a 10-15 mph SW wind.

On June 27 and June 30, estimates of dandelion and clover damage were made (Table 1 and 2). These figures represent the percentage of foliage on each plant that was damaged with 100 = all foliage damaged and dying, 50 = 50% damaged foliage, and 0 = no damaged foliage. Beginning July 7, the surviving plants were surveyed to measure broadleaf control. The number of dandelions per plot was counted July 7, July 13, July 20, July 27, August 3, and August 10 (Table 1). The percentage of dandelion cover per plot was estimated on August 3 and August 10 to account for the large numbers of small dandelions in some plots (Table 2). Clover infestation was estimated as the percentage area per plot covered by clover (Table 5).

Turf quality data were taken weekly from June 23 through August 10 (Table 6). On each date, the turf was examined for phytotoxic symptoms and none were detected. Turf quality was rated using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality. Crabgrass was appearing in the untreated and treated turf in August. The number of crabgrass plants per plot was counted on August 3 and August 10 (Table 7).

Data were analyzed using 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.

There were differences in dandelion damage levels on June 27 and June 30 both between treated and untreated and among treated plants (Table 1). Two experimental formulations, NB30196 and NB30401, caused the highest levels of damage to dandelions. These same experimentals, NB30196 and NB30401, caused the most damage on clover (Table 2). In general, none of the herbicides were as effective on clover as on dandelion through June 30.

All herbicides controlled dandelion populations significantly as compared with the untreated control (Table 3). Control was > 95% on July 7 but beyond this date some recovery and regrowth of dandelions occurred in treated plots (Table 4). This was particularly evident on August 3 in turf treated with either NB30196 or NB30401. Dandelion counts in turf treated with NB30196 at 5.0 pts/A were similar to those in the untreated turf on August 10. Percentage dandelion cover data also were similar for turf treated with NB30196 at 5.0 pts/A and for the untreated turf (Table 5).

All materials caused significant reductions in clover cover as compared with the untreated control (Tables 6 and 7). Populations were drastically reduced by July 7 and after July 27, there was no clover in any of the treated plots for the remainder of the duration of the study.

None of the herbicides caused phytotoxic symptoms on the turf. Quality was similar for treated and untreated turf for the entire period (Table 8). In August, turf quality uniformly declined because of high temperatures and sparse rainfall.

By August 3, crabgrass had moved into the treated turf. Less competition from dandelion and clover allowed larger populations of crabgrass to become established in treated as compared with untreated turf (Table 9).

Table 1. Percentage foliar damage¹ on dandelions treated for the 2000 PBI Gordon Postemergence Broadleaf Study.