Golf Course Management

JUN 2019

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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Page 77 of 139

76 GOLF COURSE MANAGEMENT 06.19 the sap test be used to guide nitrogen fertiliza- tion or assess leaf nitrogen status to minimize anthracnose? Well, the use of clipping sap was a complete fail. No relationship was found between clip- ping sap and the turf area infested with an- thracnose. e NDVI and chlorophyll meters worked better, and there was a linear relation- ship between foliar nitrogen and the NDVI/ chlorophyll readings, up to a point, after which the relationship plateaued. is plateau oc- curred at a foliar nitrogen content of 3.7% to 4.0% nitrogen in the annual bluegrass. So, if foliar nitrogen exceeded 4% nitrogen, the NDVI or chlorophyll meter did not produce a value that correlated well. Below 4% nitrogen, they did. e good part was that this foliar nitrogen content (3.7% to 4.0% N) was well beyond the critical foliar nitrogen needed to minimize an- thracnose (which is ~3.4% N), so the meters could be used to help manage foliar nitrogen to reduce anthracnose. To use this research on your golf course, fertilize a small area of your green or nursery to maximize the greening re- sponse (reference plot). Use handheld reflec- tance meters to measure the reference plot and monitor remaining greens. Fertilize remaining greens so they are at 94% to 98% of the read- ing from the reference plot for NDVI and at 73% to 93% for chlorophyll index. is should maintain sufficient foliar nitrogen (3.4% N) to minimize anthracnose severity in annual blue- grass putting green turf. Source: Inguagiato, J.C., and K. Guillard. 2016. Foliar N concentration and reflectance meters to guide N fertilization for anthrac- nose management of annual bluegrass putting green turf. Crop Science 56:3328-3337. Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and 2019 president of the Crop Science Society of America. She is a 21-year member of GCSAA. Beth Guertal, Ph.D. Twitter: @AUTurfFert That's a sappy relationship (verdure) For years and years, a basic tenet of nitro- gen (N) fertilization of turfgrass is that we base it on crop response. You watch it grow, you watch the color, and you apply nitrogen as the turf shows it's ready. is is not to say that people have not spent entire careers trying to calibrate various soil and tissue tests for nitro - gen that would allow us to make nitrogen fer- tilizer recommendations. With the advent of various remote sensing technologies, there has been a renewed interest in nitrogen fertilizer recommendations based on sensor technolo- gies, and this month's paper is a great example of that. At the University of Connecticut, John Inguagiato, Ph.D., and Karl Guillard, Ph.D., examined three different types of in-field plant nitrogen measurements, and examined how those related to nitrogen fertilization, foliar ni- trogen and anthracnose in an annual bluegrass putting green. For two years, an annual bluegrass putting green was fertilized with eight rates of nitrogen (as urea), applied every 14 days from May to August at 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.75 pound N/1,000 square feet/14 days (0, 0.24, 0.49, 0.98, 1.46, 1.95, 2.44 and 3.66 grams/square meter/14 days). e severity of anthracnose was determined by counting dam- aged areas in each plot using a line-intercept method. is was done approximately weekly in June and July of each year. At the same time that data was being collected, they also col- lected clippings from each plot, and these were dried and analyzed for total nitrogen. A sap extract was collected from fresh clippings and extracted using a plant press, and was used to determine sap nitrate-nitrogen concentration. Last, commercially available handheld meters were used to collect normalized difference veg- etative index (NDVI) and chlorophyll meter readings from each plot. e severity of the anthracnose decreased as the nitrogen rate increased, up to an estimated nitrogen rate of 0.26 pound N/1,000 square feet/14 days. is nitrogen rate was similar to those observed in previous studies. Additional nitrogen did not further reduce anthracnose. With an identified nitrogen rate for minimal anthracnose, the next question was: How well did any of the meters or the sap test predict this nitrogen status, and could the meters or Could the meters or the sap test be used to guide nitrogen fertilization or assess leaf nitrogen status to minimize anthracnose?

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