1999 Iowa Turfgrass Research Report

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 for since 1991. It is being conducted at the Iowa State University Research Station north of Ames, IA in an area of 'Parade' Kentucky bluegrass. The soil in this experimental area is a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with an organic matter content of 3.6% a pH of 7.1, 4.5 ppm P, and 101 ppm K. Individual experimental plots are 5 x 5 ft and there are 5 treatments with 3 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 lbs/1000 ft² (Table 1). Because corn gluten meal is 10% N, these rates are equivalent to 0, 2, 4, 6, 8, and 10 lb N/1000 ft². In 1998, the CGM was applied in a single early spring preemergence application on April 21 using 'shaker dispensers'. The materials were watered-in with the irrigation system. Supplemental irrigation was used to provide adequate moisture to maintain the grass in good growing condition. 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 22, May 13, May 18, May 27, June 10, June 16, July 9, July 15, July 29, August 18, and August 28 (Tables 1 and 2).

Weed control was measured by either counting the number of plants or estimating the percentage cover per individual plot. Crabgrass in the 1- to 3-leaf stage was found in the untreated turf on June 23. The crabgrass plants were large enough by July 15 to count the number per plot. Additional crabgrass count data were taken on July 29, August 18, and August 28 (Table 3). Crabgrass counts were converted to express percentage reductions in numbers as compared to the untreated controls (Table 4).

Dandelion and clover populations also were surveyed. The number of dandelions per plot was counted on July 15, July 29, August 18, and August 28 (Table 5). On these same dates, percentage clover cover data were taken. Clover cover was determined by estimating the area per plot covered by clover (Table 7). Dandelion count and percentage clover cover data were modified to express percentage reductions as compared to the untreated controls (Tables 6 and 8).

Data were analyzed with the Statistical Analysis System (SAS , Version 6.12) and the Analysis of Variance (ANOVA) procedure. Fisher’s Least Significant Difference (LSD) means comparison tests were used to assess CGM effects on bluegrass quality and weed control.

Spring greenup was obvious by April 22. Bluegrass treated with CGM had better quality than untreated turf from May 13 through June 16 (Table 1 and 2). After June 16, the season was quite hot and dry and the treated and untreated bluegrass had similar quality.

Crabgrass populations were low in the untreated controls because the dandelion and clover infestations were large and well established creating intense competition for the emerging crabgrass. Treatment with CGM at all levels except 20 lb/1000 ft² resulted in much lower crabgrass populations (Table 3). Reductions in crabgrass populations were > 91% at 40 and 60 lb/1000 ft² (Table 4). There were more crabgrass plants in turf treated with CGM at 20 lb/1000 ft² than in untreated turf (Table 3). In 1997, there also were more crabgrass plants in turf treated with CGM at 20 lb/1000 ft² as compared with the untreated control (Table 9). Reductions in crabgrass counts were similar to 1997 at all CGM levels except 40 lb/1000 ft². Much better crabgrass control was achieved at 40 lb in 1998 as compared with 1997.

Corn gluten meal at all levels except 20 lb/1000 ft² significantly reduced dandelion counts as compared with the untreated control (Table 5). Mean reductions > 72% were achieved with CGM at 40 lb and higher (Table 6). Dandelion control in 1998 was similar to control in 1997 and previous years except at the 20 lb/1000 ft² level (Table 11).

On July 29 and August 18, there was significantly less clover cover in turf treated with CGM as compared with the untreated controls (Table 7). On August 28, all CGM levels except 20 lb/1000 ft² significantly reduced clover cover. Mean reductions in clover cover were > 84% as compared with the untreated controls in turf treated with CGM at all levels except 20 lb (Table 8). Clover control in 1998 was similar to that in previous years except at 20 lb/1000 ft². At this rate, the level of clover control was much lower in 1998 as compared to 1994 through 1997 (Table 10).

Table 1 Visual quality¹ of Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

	Material	lbs CGM/ 1000 ft2	lbs N/ 1000 ft2	April 22	May 13	May 18	May 27	June 10	June 16
1	Untreated control	0	0	6.7	5.0	5.3	5.0	5.7	5.0
2	Corn gluten meal	20	2	6.3	5.7	6.3	6.3	6.3	6.3
3	Corn gluten meal	40	4	7.3	7.0	7.7	8.0	7.7	7.3
4	Corn gluten meal	60	6	8.3	8.7	8.7	8.0	8.7	8.3
5	Corn gluten meal	80	8	8.0	7.7	8.0	8.3	8.7	9.0
6	Corn gluten meal	100	10	8.3	8.3	8.3	8.0	9.0	8.7
7	Corn gluten meal	120	12	9.0	9.0	8.3	7.7	9.0	9.0
	LSD0.05			1.1	1.4	0.8	1.4	0.6	0.6

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

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.

	Material	lbs CGM/ 1000 ft2	July 9	July 15	July 29	August 5	August 18	August 28	Mean
1	Untreated control	0	6.0	6.0	6.0	6.0	6.0	6.0	5.4
2	Corn gluten meal	20	6.0	6.0	6.0	6.0	6.0	6.0	6.2
3	Corn gluten meal	40	6.0	6.0	6.0	6.0	6.0	6.0	7.5
4	Corn gluten meal	60	6.0	6.0	6.0	6.0	6.0	6.0	8.4
5	Corn gluten meal	80	6.0	6.0	6.0	6.0	6.0	6.0	8.3
6	Corn gluten meal	100	6.0	6.0	6.0	6.0	6.0	6.0	8.7
7	Corn gluten meal	120	6.0	6.0	6.0	6.0	6.0	6.0	8.7
	LSD0.05		--	--	--	--	--	--	0.6

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

-- = these data are not appropriate for means comparisons tests.

Table 3. Crabgrass count¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean counts
1	Untreated Control	0	6.3	22.7	29.7	21.3	20.0
2	Corn gluten meal	20	5.3	38.3	41.3	36.7	30.4
3	Corn gluten meal	40	3.7	1.0	0.7	1.7	1.8
4	Corn gluten meal	60	0.3	1.0	3.7	1.7	1.7
5	Corn gluten meal	80	8.7	9.0	12.0	5.7	8.8
6	Corn gluten meal	100	4.0	4.3	3.0	2.0	3.3
7	Corn gluten meal	120	1.7	7.0	6.0	4.7	4.8
	LSD0.05		NS	NS	NS	NS	NS

¹These values represent the number of crabgrass plants per plot.

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

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean reduction
			__________________________ % __________________________
1	Untreated Control	0	0.0	0.0	0.0	0.0	0.0
2	Corn gluten meal	20	15.7	0.0	0.0	0.0	0.0
3	Corn gluten meal	40	42.1	95.6	97.8	92.2	91.3
4	Corn gluten meal	60	94.7	95.6	87.6	92.2	91.7
5	Corn gluten meal	80	0.0	60.3	59.6	73.4	55.8
6	Corn gluten meal	100	36.8	80.9	89.9	90.6	83.3
7	Corn gluten meal	120	73.7	69.1	79.8	78.1	75.8
	LSD0.05		NS	NS	NS	NS	NS

¹These values represent percentage reduction in crabgrass plants per plot as compared with the untreated controls.

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

Table 5. Dandelion count¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean counts
1.	Untreated control	0	25.0	25.7	47.7	48.7	36.8
2.	Corn gluten meal	20	25.0	24.7	40.7	49.7	35.0
3.	Corn gluten meal	40	9.0	4.7	15.3	12.0	10.3
4.	Corn gluten meal	60	3.7	3.0	8.3	8.7	5.9
5.	Corn gluten meal	80	3.7	1.3	3.3	4.7	3.3
6.	Corn gluten meal	100	4.0	1.3	5.0	5.3	3.9
7.	Corn gluten meal	120	0.3	0.7	1.3	2.7	1.3
	LSD0.05		13.6	11.0	15.2	29.6	13.7

¹These counts represent the number of dandelions per plot.

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

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean reduction
			__________________________ % __________________________
1.	Untreated control	0	0.0	0.0	0.0	0.0	0.0
2.	Corn gluten meal	20	0.0	3.9	14.7	0.0	4.8
3.	Corn gluten meal	40	64.0	81.8	67.8	75.3	72.1
4.	Corn gluten meal	60	85.3	88.3	82.5	82.2	83.9
5.	Corn gluten meal	80	85.3	94.8	93.0	90.4	91.2
6.	Corn gluten meal	100	84.0	94.8	89.5	89.0	89.3
7.	Corn gluten meal	120	98.7	97.4	97.2	94.5	96.6
	LSD0.05		54.5	43.0	31.9	60.8	37.3

¹These values represent the percentage reduction in dandelions per plot as compared with the untreated controls.

Table 7. Percentage clover cover¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean cover
1.	Untreated control	0	34.7	43.3	43.3	53.3	43.7
2.	Corn gluten meal	20	35.0	21.7	30.0	41.7	32.1
3.	Corn gluten meal	40	10.7	8.3	3.3	5.3	6.9
4.	Corn gluten meal	60	6.7	7.0	5.3	6.7	6.4
5.	Corn gluten meal	80	3.3	2.0	3.7	3.7	3.2
6.	Corn gluten meal	100	7.0	3.7	2.0	5.3	4.5
7.	Corn gluten meal	120	6.7	5.3	3.7	2.3	4.5
	LSD0.05		NS	15.7	13.1	14.3	9.3

¹Percentage clover cover represents the area per plot covered by clover.

Table 8. Percentage clover cover reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study.

	Material	lbs CGM/ 1000 ft2	July 15	July 29	August 18	August 28	Mean reduction
			__________________________ % __________________________
1.	Untreated control	0	0.0	0.0	0.0	0.0	0.0
2.	Corn gluten meal	20	0.0	50.0	30.8	21.9	26.5
3.	Corn gluten meal	40	69.3	80.8	92.3	90.0	84.2
4.	Corn gluten meal	60	80.8	83.8	87.7	87.5	85.3
5.	Corn gluten meal	80	90.4	95.4	91.5	93.1	92.7
6.	Corn gluten meal	100	79.8	91.5	95.4	90.0	89.7
7.	Corn gluten meal	120	70.8	87.7	91.5	95.6	89.7
	LSD0.05		NS	36.2	30.2	26.9	21.2

¹These values represent the percentage reduction in clover cover per plot as compared with the untreated controls.

Table 9. Comparisons of the mean percentage crabgrass count reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study for 1991 through 1998.

	Material	lbs CGM/ 1000 ft2	1991	1992	1993	1994	1995	1996	1997	1998
			_____________________________ % _____________________________
1	Untreated control	0	0	0	0	0	0	0	0	0
2	Corn gluten meal	20	58	85	91	70	36	15	0	0
3	Corn gluten meal	40	86	98	98	97	88	97	79	91
4	Corn gluten meal	60	97	98	93	98	93	85	82	92
5	Corn gluten meal	80	87	93	93	87	75	69	54	56
6	Corn gluten meal	100	79	94	95	86	75	87	79	83
7	Corn gluten meal	120	97	100	100	98	84	97	82	76
	LSD0.05		26	44	31	39	40	60	NS	NS

¹These values represent the percentage reduction in crabgrass plants per plot as compared with the untreated controls.

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

Table 10. Comparisons of the mean percentage clover cover reductions¹ in Kentucky bluegrass treated in the 1991 Corn Gluten Meal Weed Control Study for 1994 through 1998.

	Material	lbs CGM/ 1000 ft2	1994	1995	1996	1997	1998
			__________________________ % __________________________
1	Untreated control	0	0	0	0	0	0
2	Corn gluten meal	20	81	56	71	63	27
3	Corn gluten meal	40	90	64	82	87	84
4	Corn gluten meal	60	98	93	93	95	85
5	Corn gluten meal	80	100	76	90	95	93
6	Corn gluten meal	100	94	84	92	76	90
7	Corn gluten meal	120	90	93	93	93	90
	LSD0.05		NS	48	29	26	21

¹Percentage clover cover represent the area per plot covered by clover.

²These values represent the percentage reduction of clover cover per plot as compared with the untreated controls.

Table 11. 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.

	Material	lbs CGM/ 1000 ft2	1994	1995	1996	1997	1998
			____________________________ % ____________________________
1	Untreated control	0	0	0	0	0	0
2	Corn gluten meal	20	71	49	33	24	5
3	Corn gluten meal	40	100	77	75	76	72
4	Corn gluten meal	60	100	89	79	84	83
5	Corn gluten meal	80	98	96	95	93	91
6	Corn gluten meal	100	100	98	96	88	89
7	Corn gluten meal	120	100	100	100	97	97
	LSD0.05		50	65	60	61	37

¹Dandelion counts represent the number of dandelions per plot.

²These values represent the percentage reduction of dandelion count per plot as compared with the untreated controls.

ISU Horticulture:Publications:1999 Turfgrass Report

College of Agriculture