1999 Iowa Turfgrass Research Report

Corn gluten hydrolysate (CGH) is an effective natural preemergent control in growth chamber and greenhouse environments. Its performance in the field may be improved by using a carrier. Two carriers for CGH are being investigated in this study, humic acid (RL 37, Liquid Seaweed Foliar from International Ag Labs, Inc., Fairmont, MN) and a soybean oil (SprayTech Oil from Agro-K Corporation, Minneapolis, MN). CGH at rates of 0, 10, 20 and 40 lb/1000 ft², humic acid at rates of 0, 1, 2 and 4 gal/acre and oil at rates of 0, 0.5, 1 and 2 pts/acre were used, with each rate of CGH being applied with each rate of humic acid and oil for a total of 32 treatments. The treatments were randomized in each of three replications. Each individual plot measured 5’x 5’. This study took place at the ISU Horticulture Research Station north of Ames, Iowa in an area with a mature stand of Kentucky bluegrass. Treatments were sprayed onto the plots on 9 May. The study area was irrigated as needed to provide a good growing condition for the turf. Weed control was determined by collecting data on percent cover of crabgrass during the season. Visual quality was also assessed during the season using a 9 to 1 scale: 9 = best quality, 6 = lowest acceptable quality, 1 = poorest quality. Analysis of data used the Statistical Analysis System version 6.12 (SAS Institute, 1989-1996).

There were 72% fewer crabgrass plants at the greatest rate of CGH (200 g·m^-2) compared to the control (Table 1). Increasing CGH rates had a positive effect on turfgrass visual quality (Table 1). Humic acid and soybean oil had no effect on the number of crabgrass plants or on turfgrass quality.

CGH applied at a rate of 200 g·m^-2 provided 72% reduction of crabgrass in this study, similar to a 66% reduction found in the first year of another CGH field study at the 200 g·m^-2 rate (Bingaman and Christians, 1996). This reduction is also similar to that of corn gluten meal, which provided 86% control when applied to turf at the 200 g·m^-2 rate (Bingaman et al., 1998). Rates of 50 and 100 g CGH per m² did not control crabgrass in this study and varied in effectiveness in previous studies by Bingaman and Christians (1996, 1997, 1998).

Applying 200 g·m^-2 CGH provides 20 g N per m², since CGH is 10% N by weight. The CGH has a fertilizing effect, improving the visual quality of the turfgrass at higher rates. Other studies have reported this fertilizing effect in both CGH (Bingaman and Christians, 1996, 1997, 1998) and corn gluten meal (Bingaman et al., 1998; Christians, 1993).

If soybean oil or humic acid had a positive effect on the herbicidal activity of the CGH, we would have seen similar crabgrass counts or quality at different rates of CGH because of the addition of soybean oil or humic acid. Only the rate of CGH had an effect on crabgrass counts and quality, so the soybean oil and humic acid treatments had no effect, neither as interactions nor as single effects.

 

Table 1. Mean number of crabgrass (Digitaria spp.) plants at the end of the 1998 growing season (16 weeks). Mean turfgrass quality from the 1998 season, rated visually: 9 = highest quality, 6 = acceptable quality, 1 = lowest quality. Each rate of corn gluten hydrolysate was applied to 10 plots in each of three replications.

Corn gluten hydrolysate (g·m-2)	Number of crabgrass plants (per 2.25 m2 plot)	Turfgrass visual quality
0	29	6.0
50	17	6.5
100	26	7.0
200	8	8.0
lsd0.05	13		0.2

REFERENCES

ISU Horticulture:Publications:1999 Turfgrass Report

College of Agriculture