APPLIED RESEARCH
Controlling Smooth Crabgrass in Tall Fescue with Pre- and Postemergence Commercial Products
By Peter H. Dernoeden, Ph.D., and C. P. Ryan, Dept. of Plant Science and Landscape Architecture, University of Maryland
his field study, which was conducted at the University of Maryland Paint Branch Turfgrass Research Facility in College Park, compared all of the commonly used preemergence herbicides that target smooth crabgrass (Digitaria ischaemum). In addition, corn gluten meal (Espoma Corn Gluten 9-0-0) was assessed and compared to the commercial products. Finally, three postemergence herbicides were applied in late June and compared to the preemergence herbicides and corn gluten meal (CGM).
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Our research methods The turf was a mature stand of Titan II tall fescue (Festuca arundinacea) and was mowed two times weekly to a height of 2.5 inches. Soil was a Keyport silt loam with a pH of 5.7 and 2.2% organic matter. Rates and dates of product applications are noted in Table 1. The site received rainfall or irrigation within 24 hours of each application. The
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MTC TURF NEWS
study site was irrigated thereafter to avoid drought stress. Turf color and quality were rated once on May 13 using a 0 to 10 scale, where 0 = entire plot area brown or dead, and 10 = optimum green color and density. Percent of the plot areas covered with smooth crabgrass was assessed visually on a 0% to 100% scale, where 0% = no crabgrass, and 100% = entire plot area covered with smooth crabgrass. Crabgrass ratings less than 5% of plot area covered (subjectively) were considered to have provided commercially acceptable control. Smooth crabgrass pressure was uniform and severe across the site.
About CGM Corn gluten meal, the protein fraction of corn, is a natural herbicide that is used to control crabgrass and other weeds in “organic lawncare programs.� Corn gluten was evaluated previously by the University of Maryland (Dernoeden, 2001). In those studies, CGM applied twice per season
reduced crabgrass populations significantly, but it did not provide commercially acceptable control. Single applications of CGM typically provided poor control. The product contains 9% to 10% nitrogen (N) and, as such, also serves as an N fertilizer. The recommended use rate of CGM is 20 lbs. product per 1,000 ft2. Hence, at this rate, a manager is delivering 1.8 to 2.0 lbs. N/1,000 ft2 with a single application. A single spring application of 2.0 lbs. N/1,000 ft2, however, is considered agronomically excessive and wasteful. The sewage sludge Oceangro 5-5-0 fertilizer was entered into the study to determine if this high rate of N (i.e., 2.0 lbs. N/1,000 ft2) from a natural organic fertilizer would impact crabgrass levels at the site. That is, the Oceangro served as a standard for comparing the potential influence of organic N on crabgrass invasiveness in the study site. The levels of N delivered via CGM and Oceangro resulted in excellent turf color and quality (8.8