Various formulations of Barricade on a fertilizer carrier were screened to determine the lowest herbicide rate that would provide an acceptable level of crabgrass control. This study was conducted at Iowa State University Horticulture Research Station. The experimental area was seeded in Fall 1998 with 'Moonlight' Kentucky bluegrass. The soil in this area was a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with an organic matter content of 3.8%, a pH of 7.1, 12 ppm P, and 128 ppm K. In the spring of 1999, the plot had approximately 50% bluegrass cover. This area had a history of heavy crabgrass infestations so no overseeding of crabgrass was performed.

The experimental design was a randomized complete block. Individual plot size was 5 x 5 ft with three replications. There were a total of 19 treatments including Dimension 1EC and experimental formulations of Dithiopyr. Dimension, Team Pro, Pendimethalin, and Barricade were screened in formulations on fertilizer. Other experimental formulations also were included with an untreated control (Table 1).

Table 1. Products and application rates for the 1999 Preemergent Annual Grass Study.

Treatments 2 - 12 and initial applications of 13-18 were made April 30 before crabgrass germination. Sequential applications of treatments 13 and 15 were made on June 24, 8 to 10 weeks after the initials.

All materials were applied on April 30. Granular treatments were made using cardboard cartons as 'shaker dispensers' to ensure even distribution of product. Liquid materials were dissolved in 283 ml water (which is equivalent to a rate of 3 gal/1000 ft²) and were applied at 30-35 psi using a carbon dioxide backpack sprayer equipped with TeeJet #8006 flat fan nozzles.

The plot was checked May 3 for phytotoxicity and none was observed. Visual quality ratings were made weekly from May 10 through September 14 (Tables 2 and 3). Quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst quality. Crabgrass count data were taken weekly from May 10 through September 14 (Table 4). In addition, data were taken for all weed species present on September 1, 9, and 14 (Table 5). Data were analyzed with the Statistical Analysis System (SAS, version 6.12) and the Analysis of Variance (ANOVA) procedure. Means were compared with Fisher's Least Significant Difference (LSD) tests.

The quality of the 'Moonlight' bluegrass was not affected by any of the treatments. Even the herbicide plus fertilizer formulations had no effect on quality. This bluegrass cultivar has a dark, blue-green color and differences in color were not detectable. Thickness and uniformity also were similar for untreated and treated bluegrass.

There were very few crabgrass plants in the experimental area even in the surrounding fringe areas. This can probably be explained by a low germination rate of crabgrass and/or the aggressive nature of this bluegrass cultivar. It has been noted from other studies that crabgrass populations are low in bluegrass plots during the establishment year. This study area will be monitored spring and summer 2000 for differences in quality and crabgrass numbers. In addition, another area was planted with 'Moonlight' and other standard bluegrass cultivars so crabgrass populations within the establishment year can be monitored.

Broadleaf weed species were prevalent within this test area early spring 1999. As the bluegrass filled in the area, the weeds were outcompeted and by September their numbers were very low. Dandelion was the only species that was found in more than two individual plots.

Table 2. Visual quality¹ of 'Moonlight' Kentucky bluegrass treated for the 1999 Preemergent Annual Weed Control Study (May 10 through July 14).

Table 3. Visual quality¹ of 'Moonlight' Kentucky bluegrass treated for the 1999 Preemergent Annual Weed Control Study (June 21 through September 14).