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Title: Racer as a potential organic herbicide: Application volumes and herbicide rates

Author
item Webber Iii, Charles
item BRANDENBERGER, LYNN - OSU, STILLWATER, OK
item SHREFLER, JAMES - OSU, LANE, OK
item WELLS, LYNDA - OSU, STILLWATER, OK
item SHANNON, KENT - UNIV. OF MISSOURI

Submitted to: Extension Publications
Publication Type: Other
Publication Acceptance Date: 2/5/2008
Publication Date: 4/1/2008
Citation: Webber III, C.L., Brandenberger, L.P., Shrefler, J.W., Wells, L.K., Shannon, K. 2008. Racer as a potential organic herbicide: Application volumes and herbicide rates. In: Brandenberger, L., Wells, L., editors. 2007 Vegetable Trials Report. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture and Landscape Architecture. Stillwater, OK. MP-162. p. 15-17.

Interpretive Summary: In a national survey it was determined that weed control research was the number one priority for organic vegetable producers. Racer is labeled for non-food use and efforts are currently underway to label it as a bio-herbicide for organically grown food crops. The main component of Racer is ammonium pelargonate which occurs in nature and is primarily formed from biodegradation of higher fatty acids. As a contact herbicide, the application volume could be an important factor in determining the effectiveness of this herbicide. The objective of this study was to investigate impact of application rates and volumes on the weed control efficacy of Racer on endemic weed populations. The field experiment was conducted on a Bernow fine sandy loam at Lane, OK. The experiment consisted of 9 weed control treatments, which included 2 herbicide rates (6.4 and 9.6 lb/a) applied at 4 application volumes (17.5, 35, 70, and 105 gpa), plus an untreated weedy-check. Racer was applied as a broadcast application on September 12 using a tractor mounted CO2 sprayer equipped with four extended range, stainless steel, 0.3 gal/min nozzles, on 20-inch spacings at a spraying height of 20 inches. To maintain the same spray pattern for each weed control treatment, the nozzle pressure was held constant and tractor speed adjusted to achieve the different overall application rates (17.5, 35, 70, and 105 gpa). At the time of application, tumble (Amaranthus albus L.) and spiny (Amaranthus spinosus L.) pigweeds were 1-1.5 inch tall, carpetweeds (Mollugo verticillata L.) were 1.0 inch across with 5-7 leaves, and grasses, goosegrass (Eleusine indica L. Gaertn.), and smooth crabgrass (Digitaria isahaemum (Schreb. ex Schweig) Schreb. ex Muhl.) had 2-3 leaf shoots, each about 2-3 inches long. Plots were rated on September 18, 6 days after planting, for percent weed control on a 0 to 100% scale, where 0% equals no weed control and 100% equals complete control (i.e. dead plants). In general, the application of Racer produced greater weed control for the broadleaf weed species (tumble pigweed, spiny pigweed, and carpetweed) than the grass weeds (goosegrass and smooth crabgrass). Although all of the Racer applications produced significantly greater weed control for all weed species compared to the weedy-check, there were no significant differences among Racer applications for grass weed control. Grass weed control ranged from 30 to 52.5% for goosegrass and 22.5 to 52.5% for smooth crabgrass. The range and magnitude of the broadleaf weed control was much greater than the grass weed control. The best weed control for both pigweed species occurred at the 9.6 lb/a rate applied at 70 gpa. Carpetweed was very sensitive to Racer, resulting in 65% control at the lowest application rate and volume, and most application rates and volumes resulting in, at least, 85% control. The results indicate that Racer has an excellent potential as an effective organic herbicide if it achieves the proper clearance. As with other contact herbicides, organic and non-organic herbicides, Racer provide greater weed control for broadleaf weeds than grass weeds. It is also important to note that Racer provided consistent control across a large range of application volumes.

Technical Abstract: Racer (40% ammonium pelargonate/ammonium nonanoate) is labeled for non-food use and efforts are currently underway to label it as a bio-herbicide for organically grown food crops. The main component of Racer is ammonium pelargonate which occurs in nature and is primarily formed from biodegradation of higher fatty acids. The objective of this study was to investigate impact of application rates and volumes on the weed control efficacy of Racer on endemic weed populations. The field experiment was conducted on a Bernow fine sandy loam at Lane, OK. The experiment consisted of 9 weed control treatments, which included 2 herbicide rates (6.4 and 9.6 lb/a) applied at 4 application volumes (17.5, 35, 70, and 105 gpa), plus an untreated weedy-check. Racer was applied as a broadcast application on September 12 using a tractor mounted CO2 sprayer equipped with four extended range, stainless steel, 0.3 gal/min nozzles, on 20-inch spacings at a spraying height of 20 inches. To maintain the same spray pattern for each weed control treatment, the nozzle pressure was held constant and tractor speed adjusted to achieve the different overall application rates (17.5, 35, 70, and 105 gpa). At the time of application, tumble (Amaranthus albus L.) and spiny (Amaranthus spinosus L.) pigweeds were 1-1.5 inch tall, carpetweeds (Mollugo verticillata L.) were 1.0 inch across with 5-7 leaves, and grasses, goosegrass (Eleusine indica L. Gaertn.), and smooth crabgrass (Digitaria isahaemum (Schreb. ex Schweig) Schreb. ex Muhl.) had 2-3 leaf shoots, each about 2-3 inches long. Plots were rated on September 18, 6 days after planting, for percent weed control on a 0 to 100% scale, where 0% equals no weed control and 100% equals complete control (i.e. dead plants). In general, the application of Racer produced greater weed control for the broadleaf weed species (tumble pigweed, spiny pigweed, and carpetweed) than the grass weeds (goosegrass and smooth crabgrass). Although all of the Racer applications produced significantly greater weed control for all weed species compared to the weedy-check, there were no significant differences among Racer applications for grass weed control. Grass weed control ranged from 30 to 52.5% for goosegrass and 22.5 to 52.5% for smooth crabgrass. The range and magnitude of the broadleaf weed control was much greater than the grass weed control. The best weed control for both pigweed species occurred at the 9.6 lb/a rate applied at 70 gpa. Carpetweed was very sensitive to Racer, resulting in 65% control at the lowest application rate and volume, and most application rates and volumes resulting in, at least, 85% control. The results indicate that Racer has an excellent potential as an effective organic herbicide if it achieves the proper clearance. As with other contact herbicides, organic and non-organic herbicides, Racer provide greater weed control for broadleaf weeds than grass weeds. It is also important to note that Racer provided consistent control across a large range of application volumes.