1998 Iowa Turfgrass Research Report

1998 Iowa Turfgrass Research Report

1995 Corn Gluten Hydrolysate Weed Control Study - Year 3

Barbara R. Bingaman, Nick E. Christians, and Michael B. Faust

Corn gluten hydrolysate (CGH) was screened for efficacy as a natural herbicide in turf. This trial is a long-term study started in 1995 that will be continued in the same experimental area for several years. It is being conducted at the Iowa State University Research Station north of Ames, IA. The experiment is located in an area of 'Ram 1' Kentucky bluegrass. The soil in this area is a Nicollet (fine-loamy, mixed, mesic Aquic Hapludoll) with an organic matter content of 3.7% a pH of 7.1, 5 ppm P, and 100 ppm K.

The experimental design is a randomized complete block. Individual experimental plots are 5 x 5 ft with three replications. There are 3-ft barrier rows between replications. Corn gluten hydrolysate was applied at 5, 10, 15, and 20 lbs product/1000 ft² (Table 1). These rates translate to 0.5, 1.0, 1.5, and 2.0 lbs N/1000 ft². The CGH was dissolved in water and the volumes applied were 700, 1400, 2100, and 2800 ml for the 5, 10, 15, and 20 lb rates, respectively. An untreated control was included for comparisons. A liquid seaweed foliar feeding product (0.2-0-1), RL-37, from International Ag Labs, Inc. was applied to the south half of the plots in replication 1 at 3 oz product/1000 ft². This product is supposed to stabilize the CGH and prolong the CGH effects. The CGH was applied at 20 psi using a carbon dioxide backpack sprayer equipped with TeeJet™ #8006 flat fan nozzles.

All treated plots received a single application on May 9. A wind barrier was used as a windbreak to prevent sprayer drift. The treatments were watered in with irrigation. Supplemental irrigation was used throughout the season to maintain the grass in good growing condition.

Visual quality data were taken on May 21, June 5, June 10, June 18, July 21, July 30, and August 20. Visual quality was measured using a 9 to 1 scale: 9 = best, 6 = lowest acceptable, and 1 = worst quality (Table 1). Weed populations were very high especially in the untreated controls. The percentage of area per plot covered by all weed species was estimated on May 12 and June 5 (Table 2). On July 30, the percentage of area per plot covered by broadleaf weed species was determined (Table 2). Crabgrass control was assessed by counting the number of crabgrass plants per plot on July 30 and August 20 (Table 3). In addition, weed control data were taken on August 20 for dandelion, clover, and black medic. The number of dandelion plants per plot were counted and the percentages of clover and black medic cover were estimated per plot (Table 4).

Data were analyzed with the Statistical Analysis System version 6.10 (SAS Institute, 1989) using the Analysis of Variance (ANOVA) procedure. Fisher's Least Significant Difference (LSD) means comparisons were used to assess hydrolysate effects on bluegrass quality and weed control.

No phytotoxic symptoms were detected in any of the treated plots. Turf quality was improved by CGH as compared with the untreated control plots through July 30. By August 20, there were no differences in quality between the treated and untreated turf.

Total weed populations were not significantly reduced by CGH (Table 2). On some of the data collection dates, weed cover was higher in bluegrass treated with CGH than in the untreated control. The majority of the weed cover was dandelion and clover.

Crabgrass populations were reduced by CGH as compared with the untreated control (Table 3). The higher rates of CGH provided the best control.

Corn gluten hydrolysate at 10, 15, and 20 lb caused numerical reductions in the number of dandelions per plot but the reductions were not statistically significant (Table 4). There were more dandelions in turf treated with CGH at 5 lb than in the untreated control. Percentage clover cover was not reduced by CGH. The percentage cover in all CGH treated turf was equal to or greater than the cover in the untreated control. Black medic cover was numerically reduced by CGH at 15 and 20 lb but the differences as compared to the untreated control and the other treated turf were not statistically significant. There was more black medic in turf treated with CGH at 5 and 10 lb than in the untreated control.

Table 1. Visual quality¹ of Kentucky bluegrass in the 1995 Corn Gluten Hydrolysate Weed Control Study.

		Rate lb/1000 ft2	May 21	June 5	June 10	June 18	July 212	July 30	Aug 20	Mean
1	Untreated control	NA	6	6	6	6	6	6	6	6
2	CGH	5	7	6	6	6	6	6	6	6
3	CGH	10	7	8	7	7	7	7	6	7
4	CGH	15	7	8	9	8	7	8	6	8
5	CGH	20	8	8	8	8	7	8	6	8
	LSD0.05		1	1	1	1	1	1	NS	1

¹Visual quality was assessed using a 9 to 1 scale: 9 = best, 6 = lowest acceptable, and 1 = worst quality.

²Means are significantly different at the 0.07 level.

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

Table 2. Percentage total weed cover¹ and percentage broadleaf weed cover² in Kentucky bluegrass in the 1995 Corn Gluten Hydrolysate Weed Control Study.

			Percentage weed cover				Percentage broadleaf cover
		Rate lb/1000 ft2	May 12	June 5	Mean		July 30
			______________ % ______________				_____ %_____
1	Untreated control	NA	62	70	66		23
2	CGH	5	60	75	68		37
3	CGH	10	47	62	54		32
4	CGH	15	43	62	53		15
5	CGH	20	60	62	61		38
	LSD0.05		NS	NS	NS		NS

¹ These figures represent the total percentage area per plot covered by all weed species.

²These figures represent the percentage are per plot covered by broadleaf weed species.

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

Table 3. Crabgrass counts¹ in Kentucky bluegrass in the 1995 Corn Gluten Hydrolysate Weed Control Study.

			Crabgrass counts
		Rate lb/1000 ft2	July 30	August 20	Mean
1	Untreated control	NA	20	27	24
2	CGH	5	12	20	16
3	CGH	10	4	10	8
4	CGH	15	2	13	7
5	CGH	20	4	4	4
	LSD0.05		10	10	8

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

Table 4. Dandelion counts, percentage clover cover, and percentage black medic cover¹ in Kentucky bluegrass in the 1995 Corn Gluten Hydrolysate Weed Control Study.

		Rate lb/1000 ft2	Dandelion count		Clover cover		Black medic cover
					____ % ____		____ % ____
1	Untreated control	NA	76		13		7
2	CGH	5	96		15		12
3	CGH	10	64		15		12
4	CGH	15	60		13		1
5	CGH	20	61		17		4
	LSD0.05		NS		NS		NS

¹These figures represent the number of dandelions per plot and the percentage area per plot covered by clover and black medic.

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

ISU Horticulture:Publications:1998 Turfgrass Report

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