This was the first year of an ongoing study that was established in 1999 to determine if 'Moonlight' Kentucky bluegrass could suppress crabgrass populations. The 1998 Preemergence Annual Weed Control Study was conducted in an area of 'Moonlight' that was seeded in the fall of 1997. At the time of treatment in April 1998, approximately 50% of the area was covered by 'Moonlight'. This cultivar quickly filled in the bare areas and at the end of the season, the plot was covered by very dense turf with no crabgrass even in the untreated areas. There were no additional herbicide treatments on this plot so it was speculated that this cultivar either may possess some allelopathic properties or could be particularly aggressive in the establishment year.

This study is being conducted at the Iowa State University Horticulture Research Station. Individual 5 x 5 ft plots in a prepared bare soil area were seeded with 'Moonlight', 'Kenblue', 'Blue Moon', 'Rugby II', and 'Park' Kentucky bluegrass at 1.5 lb/1000 ft² on October 5, 1999. The soil in this area is a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with an 1.9% organic matter, pH of 7.25, 35 ppm P, and 62 ppm K. Seeding was done by hand for each individual plot to ensure uniform distribution. Each individual plot was carefully raked following seeding. Three replications were performed. No herbicides were applied prior to or following seeding.

Turf establishment was measured by estimating the percentage area per plot covered by turf. Percentage turfgrass cover data were taken from April 26 through August 29 (Table 1). Crabgrass populations were determined by estimating the percentage area per plot covered by crabgrass. Crabgrass data were taken on July 21, August 2, August 8, August 16, August 24, and August 29 (Table 2).

Data were analyzed using the Statistical Analysis System (SAS Institute Inc., 1996) and the Analysis of Variance (ANOVA) procedure. Means comparisons were made using Fisher's Least Significant Difference (LSD) test.

There were significant differences throughout the season in percentage turf cover (Table 1). 'Kenblue' and 'Park' established quicker than 'Moonlight', 'Blue Moon', and 'Rugby II'. By August 29, 'Moonlight' covered 51.7% of its plots while 'Kenblue' and 'Park' covered 85 and 76.7%, respectively.

Because there was less competition from turf plants, higher numbers of crabgrass plants were able to establish in plots with less turf cover (Table 2). There was significantly less crabgrass in 'Kenblue' than in 'Moonlight' plots for the entire season.

These establishment year data show that 'Moonlight' did not exhibit a more aggressive growth than the other tested cultivars. In addition, there was no indication of allelopathic properties for 'Moonlight'. The 2000 growing season was particularly dry and warm and it is possible that these climatic factors may have affected the establishment of the cultivars. Additional data for both turfgrass and crabgrass cover will be taken in 2001.

Table 1. Percentage turfgrass cover¹ in the 1999 Kentucky Bluegrass Crabgrass trial.