Golf Course Management

MAY 2019

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05.19 GOLF COURSE MANAGEMENT 65 (Table 1). Applying iron sulfate at a seven-day interval was much more effective than appli - cations at a 14-day interval (Table 2). Urea, alone or in combination with other products, was not consistently effective at reducing dol - lar spot at the rates used in this study. Iron sulfate mixed with Emerald (boscalid, BASF) was extremely effective at suppressing dollar spot at the Minnesota location; however, Em - erald did not effectively control dollar spot at the Wisconsin site. e poor control provided in Wisconsin may be an indication of fungi - cide resistance to Emerald, which has been repeatedly used at the research facility over many years. Objective 2. At both sites, there was a clear dose response within the seven-day reapplica - tion interval where higher rates of iron sulfate resulted in less dollar spot. e greatest dol - lar spot reduction was provided by iron sulfate applied at 12 fluid ounces/1,000 square feet (38.2 liters/hectare) every seven days, but this resulted in a very dark color that may be un - desirable for superintendents. No strong influ- ence of water volume on dollar spot severity was observed. Summary Iron sulfate provided significant suppres- sion of dollar spot in the first year of this two- year study at sites in Wisconsin and Minne - sota. e seven-day reapplication interval was almost always more effective than the 14-day interval, suggesting that lower rates at shorter intervals is a more effective iron sulfate use strategy than higher rates at longer intervals. e urea treatments in this study did not con - sistently reduce dollar spot. e study will be repeated at both locations in year 2, but the fungicide treatment will be changed to ac - count for the possibility of fungicide resistance at the Wisconsin research station. Literature cited 1. Mattox, C.M., A. Kowalewski, B. McDonald, J.G. Lambrinos, B. Daviscourt and J. Pscheidt. 2017. Nitrogen and iron sulfate affect Microdochium patch severity and turf quality on annual bluegrass putting greens. Crop Science 57:S:-293-S-300. 2. McCall, D.S., E. Ervin, C. Shelton, N. Reams and S. Askew. 2016. Influence of ferrous sulfate and its elemental components on dollar spot suppression. Crop Science 57: 581-586. 3. Reams, N.F. 2013. The effect of Fe-sulfate on annual bluegrass, silvery thread moss, and dollar spot popu - Treatments for dollar spot severity in Wisconsin Treatment Rate/1,000 square feet Application interval Dollar spot severity* Aug. 8 1 Non-treated control 162.8 abc 2 Urea 0.1 pound N † 7 day 156.0 abc 3 Urea 0.2 pound N 14 day 139.8 b-e 4 Urea Emerald 0.2 pound N 0.18 ounce 14 day 28 day 120.8 b-e 5 Urea Emerald 0.2 pound N 0.18 ounce 14 day 42 day 94.5 ef 6 Iron sulfate 6 ounces 7 day 69.5 f 7 Iron sulfate 6 ounces 14 day 168.3 ab 8 Iron sulfate Emerald 6 ounces 0.18 ounce 14 day 28 day 147.5 a-d 9 Iron sulfate Emerald 6 ounces 0.18 ounce 14 day 42 day 155.8 abc 10 Urea Iron sulfate 0.1 pound N 6 ounces 7 day 97.5 ef 11 Urea Iron sulfate 0.2 pound N 6 ounces 14 day 128.5 b-e 12 Urea Iron sulfate Emerald 0.2 pound N 6 ounces 0.18 ounce 14 day 14 day 28 day 100.5 def 13 Urea Iron sulfate Emerald 0.2 pound N 6 ounces 0.18 ounce 14 day 14 day 42 day 128.3 b-e 14 Emerald 0.18 ounce 28 day 118.3 c-f 15 Emerald 0.18 ounce 42 day 195.5 a *Means in the same column followed by the same letter are not significantly different. † N, nitrogen. Table 1. At the Madison, Wis., site, there were 15 treatments, including an untreated control. Treatments included urea, iron sulfate, or Emerald alone or in combinations of all three products, or urea + Emerald, urea + iron sulfate or iron sulfate + Emerald. Urea and iron sulfate were both applied at intervals of seven or 14 days, whether they were applied singly or in the same treatment. Emerald was applied at intervals of 28 or 42 days, whether it was applied singly or in the same treatment as iron sulfate or urea or both. 0.1 pound/1,000 square feet = 4.9 kilograms/hectare, 0.2 pound/1,000 square feet = 9.8 kilograms/hectare, 0.18 ounce/1,000 square feet = 0.5 kilogram/hectare and 6 ounces/1,000 square feet = 18.3 kilograms/hectare.

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