A study screening corn gluten meal (CGM) for efficacy as a natural product herbicide and fertilizer in turf has been continued on the same plot at the Iowa State University Research Station north of Ames, IA since 1991. The experimental area is established 'Parade' Kentucky bluegrass and the soil is a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with organic matter of 4.0%, pH of 7.2, 4.5 ppm P, and 107 ppm K. Individual experimental plots are 5 x 5 ft and there are five treatments with three replications. The experimental design is a randomized complete block. Corn gluten meal is applied each year to the same plots at 0, 20, 40, 60, 80, 100, and 120 lb/1000 ft² (Table 1). Because CGM is 10% N, these rates are equivalent to 0, 2, 4, 6, 8, 10, and 12 lb N/1000 ft². The CGM is applied each year in a single early-spring preemergence application using 'shaker dispensers'. The materials are watered-in with the irrigation system. Supplemental irrigation is used to provide adequate moisture to maintain the grass in good growing condition. In 1999, applications were made on April 30.

The plot was monitored throughout the season for turf quality. Visual turf quality was assessed using a 9 to 1 scale with 9 = best, 6 = lowest acceptable, and 1 = worst turf quality. Quality data were taken on April 21, May 10, May 26, June 2, June 8, June 15, June 24, July 1, July 7, July 14, July 22, July 27, August 3, August 11, August 19, August 24, August 31, September 7, and September 14 (Tables 1 and 2).

Weed populations were measured by either counting the number of plants or estimating the percentage cover per individual plot. Percentage weed cover data (including all broadleaf weed species) were taken early in the season. Weed cover data were recorded on April 21, April 28, and June 2 and represent the area covered by broadleaf weeds in each plot (Tables 3 and 4). Beginning on July 1, separate weed data were taken for clover and dandelion. Clover populations were assessed by estimating the percentage clover cover per plot (Tables 9 and 10). Dandelion plants were counted in each plot (Tables 7 and 8).

Crabgrass plants in the 1- to 3-leaf growth stage were found late in June and they were large enough by July 22 to count. Subsequent counts were made on July 27, August 3, August 11, August 19, August 24, August 31, September 7, and September 14 (Tables 5 and 6).

Data were analyzed with the Statistical Analysis System (SAS, Version 6.12) and the Analysis of Variance (ANOVA) procedure. Effects of CGM on bluegrass quality and weed control were examined using Fisher’s Least Significant Difference (LSD) means comparison tests. To better express weed control, weed population data were converted to percentage reductions as compared to the untreated controls.

At spring greenup in April, there were no quality differences between treated and untreated turf (Table 1). By late May, the quality of CGM treated grass was significantly better than untreated grass. The improved quality of treated bluegrass lasted for much of the season. During the hottest and driest period in mid- to late July, the quality of treated and untreated grass deteriorated (Tables 1 and 2). Once the temperatures moderated, CGM-treated grass exhibited better quality than untreated and the quality differences were still evident in September.

Percentage weed cover was significantly decreased by all CGM rates except 20 lb/1000 ft² as compared with the untreated controls (Tables 3 and 4). On June 2, reductions were at least 62% for CGM rates above 20 lb/1000 ft² and were „ 80% for the 80 and 120 lb rates.

Crabgrass populations were drastically reduced by CGM from July through September at all rates except 20 lb/1000 ft² (Tables 5 and 6). Mean crabgrass reductions for the entire season were „ 95% for all CGM rates except 20 lb/1000 ft² (Table 6). There were more crabgrass plants in turf treated with CGM at 20 lb/1000 ft² than in untreated turf for much of the season (Table 5). In 1997 and 1998, there also were more crabgrass plants in turf treated with CGM at 20 lb/1000 ft² as compared with the untreated control (Table 11). Crabgrass control at all CGM levels was better in 1999 than in previous years.

Dandelion counts were significantly reduced by CGM at all levels except 20 lb/1000 ft² as compared with the untreated controls (Tables 7 and 8). Mean reductions were at least 77% for CGM at 40 lb and higher and greater than 92% for CGM at 60 lb and higher. Dandelion control in 1999 was better than either 1998 or 1997 except at the 20 lb/1000 ft² level (Table 13).

Percentage clover cover was significantly reduced in turf treated with CGM as compared with the untreated controls (Tables 9 and 10). Mean reductions in clover cover were > 81% as compared with the untreated controls in turf treated with CGM at all levels except 20 lb (Table 10). Clover control in 1999 was similar to that in previous years except at 20 lb/1000 ft². At this rate, the level of clover control was higher in 1999 than 1998 but still lower than in previous years (Table 12).

NS = means are not significantly different at the 0.05 level.

Table 2. Visual quality¹ of Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study (July 14 through Sept. 14).

NS = means are not significantly different at the 0.05 level.

NS = means are not significantly different at the 0.05 level.

Table 4. Percentage weed cover reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

NS = means are not significantly different at the 0.05 level.

NS = means are not significantly different at the 0.05 level.

Table 6. Crabgrass count reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

NS = means are not significantly different at the 0.05 level.

Table 7. Dandelion counts¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

Table 8. Dandelion count reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

NS = means are not significantly different at the 0.05 level.

Table 9. Percentage clover cover¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

Table 10. Percentage clover cover reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

NS = means are not significantly different at the 0.05 level.

Table 11. Comparisons of the mean crabgrass count reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study for 1991 through 1999.

NS = means are not significantly different at the 0.05 level.

Table 12. Comparisons of the mean percentage clover cover reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study for 1994 through 1999.

NS = means are not significantly different at the 0.05 level.

Table 13. Comparisons of the mean percentage dandelion count reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study for 1994 through 1998.