Golf Course Management

FEB 2018

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 90 of 119

02.18 GOLF COURSE MANAGEMENT 77 when attempting to manage anthracnose. Light-rate, frequent fertilization (spoon- feeding) of nitrogen during the summer is highly effective at suppressing anthracnose (14). In research trials where anthracnose was not treated with fungicides, fertiliza - tion at 0.1 to 0.2 pound of nitrogen/1,000 square feet (0.49-0.98 gram/square meter) per week greatly reduced disease severity (14, 27). In fact, in some years, 0.1 pound of ni - trogen/1,000 square feet/week along with the correct combination of other cultural prac - tices (for example, mowing height and sand topdressing) sufficiently suppressed the dis - ease to the point that some might consider fungicide control unnecessary (12). Although some superintendents might consider 0.1 pound of nitrogen/1,000 square feet a rather high rate, it is not excessive for managing anthracnose. Under high disease pressure, up to 0.2 pound of nitrogen/1,000 square feet/week may be required to pro - vide optimal disease suppression. Anthrac- nose did not intensify until researchers ap- plied extremely high rates of nitrogen (≥0.3 pound/1,000 square feet; 1.46 grams/square meter per week) on putting greens (27). The studies cited here have identified a range of nitrogen rates and frequencies rec - ommended for managing this disease. How- ever, differences in length of growing season, soils and weather can also influence nitrogen fertility requirements. The key is to maintain sufficient nitrogen in the plant (~3.35% nitro - gen in leaf tissue) through frequent, light-rate applications of soluble nitrogen to optimize anthracnose suppression (13). Tissue testing of clippings offers superintendents a strategy, other than calendar-based fertilization, to fine-tune spoon-feeding applications to opti - mize anthracnose control, independent of site and seasonal differences. Superintendents need to consider factors other than anthracnose that affect the need for nitrogen, including playability, intensity of traffic, and vigor of the turf, as well as man - agement intensity (mowing, pest pressure, cultivation, irrigation, etc.). Frequent plant growth regulator applica - tions are an effective tactic for maintaining green speed and for eliminating excess verti - cal shoot growth caused by light-rate, frequent nitrogen fertilization. Studies evaluating trinexapac-ethyl (Primo MAXX, Syngenta), mefluidide (Embark, PBI-Gordon) and eth - ephon (Proxy, Bayer) alone or in combina- tion have shown that these products will not intensify anthracnose severity (14,16,17). And there is evidence that these plant growth reg - ulators may, in some instances, subtly reduce anthracnose so that seedheads are suppressed and plant vigor is enhanced (4,14,16,17). Al - though small and inconsistent reductions in anthracnose were observed when trinexapac- ethyl was applied every 14 days, applications based on the 200-growing-degree-day model Symptoms of anthracnose disease of annual bluegrass include yellow leaf spots with small, black, spore-bearing structures called acervuli. In this photo, some of the leaves have turned brown and are sprinkled with the spore-bearing structures.

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